U.S. patent application number 10/795241 was filed with the patent office on 2004-09-02 for bird's-eye view forming method, map display apparatus and navigation system.
Invention is credited to Endo, Yoshinori, Fujiwara, Toshio, Hirano, Motoki, Kishi, Norimasa, Satake, Hiroyuki, Shojima, Hiroshi, Watanabe, Masaki.
Application Number | 20040169653 10/795241 |
Document ID | / |
Family ID | 26436756 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040169653 |
Kind Code |
A1 |
Endo, Yoshinori ; et
al. |
September 2, 2004 |
Bird's-eye view forming method, map display apparatus and
navigation system
Abstract
In a navigation system using a bird's-eye view display mode, map
data on a plan view map are subjected to a perspective projection
conversion to obtain drawing data on a bird's-eye view map. In this
case, an input of the position of a view point is accepted, and a
projection plane for a bird's-eye view is determined on the basis
of the coordinates of a current position and a destination and the
position of the view point so that the display positions of the two
points which have been subjected to perspective-projection
conversion are coincident with predetermined positions.
Alternatively, an input of a scale is accepted, and the position of
the view point and the projection plane are determined on the basis
of the coordinates of the two points and the scale so that the
display positions of the two points after the perspective
projection conversion are coincident with predetermined positions
and the drawing scale is coincident with the input scale. Or, as a
further alternative, an input of the projection angle is accepted,
and the projection plane is determined on the basis of the
projection angle and the position of the view point.
Inventors: |
Endo, Yoshinori; (Mito-shi,
JP) ; Fujiwara, Toshio; (Hitachi-shi, JP) ;
Satake, Hiroyuki; (Hitachi-shi, JP) ; Shojima,
Hiroshi; (Kashiwa-shi, JP) ; Kishi, Norimasa;
(Yokohama-shi, JP) ; Watanabe, Masaki;
(Yokohama-shi, JP) ; Hirano, Motoki; (Tokyo,
JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
26436756 |
Appl. No.: |
10/795241 |
Filed: |
March 9, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10795241 |
Mar 9, 2004 |
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10458164 |
Jun 9, 2003 |
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6760027 |
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10458164 |
Jun 9, 2003 |
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09853547 |
May 11, 2001 |
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6654014 |
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09853547 |
May 11, 2001 |
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09497932 |
Feb 4, 2000 |
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6346942 |
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09497932 |
Feb 4, 2000 |
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08632791 |
Apr 17, 1996 |
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6141014 |
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Current U.S.
Class: |
345/427 ;
345/419 |
Current CPC
Class: |
G09B 29/106 20130101;
G01C 21/3635 20130101; G01C 21/3673 20130101; G01C 21/367
20130101 |
Class at
Publication: |
345/427 ;
345/419 |
International
Class: |
G06T 015/20 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 1995 |
JP |
7-95535 |
Claims
What is claimed is:
1. A map display apparatus comprising: an image display device; map
storage means for storing map data to display maps; and map drawing
means for preparing drawing data of a map using said map data read
out from said map storage means and displaying an image of the map
on said image display device on the basis of the drawing data,
wherein said map drawing means includes coordinate transforming
means for transforming coordinate data contained in the map data,
and said coordinate transforming means includes perspective
projection means for perspectively projecting the coordinate data
contained in the map data onto a predetermined projection plane
with a view point at a desired position to thereby prepare the
drawing data of a bird's-eye view.
2. The map display apparatus as claimed in claim 1, further
comprising an input device, wherein said coordinate transforming
means further includes means for accepting an input of the position
of the view point through said input device, and means for
determining the projection plane on the basis of predetermined two
points contained in the map data and the input view point position
so that the drawing positions of the two points after the
perspectively projecting operation are coincident with
predetermined positions.
3. The map display apparatus as claimed in claim 1, further
comprising an input device, and wherein said coordinate
transforming means further includes means for accepting an input of
a scale through said input device, and means for determining the
position of the view point and the projection plane on the basis of
the coordinates of two predetermined points contained in the map
data and the input scale so that the drawing positions of the two
points after the perspectively projecting operation are coincident
with predetermined positions, and the scale of a drawn map on the
projection plane is coincident with the input scale.
4. The map display apparatus as claimed in claim 1, further
comprising an input device, and wherein said coordinate
transforming means further includes means for accepting, through
said input device, an input of a projection angle which is an
intersection angle between the projection plane and a plane on
which the map data are defined, and means for determining the
projection plane on the basis of the input projection angle and the
position of the view point.
5. The map display apparatus as claimed in claim 1, further
comprising means for preparing drawing data of a plan view without
performing the perspective projection processing, and drawing
determining means for determining one of the bird's-eye view and
the plan view for which the drawing data should be prepared.
6. The map display apparatus as claimed in claim 5, further
comprising an input device, and wherein said coordinate
transforming means further includes drawing selection accepting
means for accepting, through said input device, an instruction
indicating one of the bird's-eye view and the plan view for which
the drawing data are prepared, and wherein said drawing determining
means determines the drawing data to be prepared in accordance with
the accepted instruction of said drawing selection accepting
means.
7. The map display apparatus as claimed in claim 5, wherein said
map drawing means further includes projection angle changing means
for instructing said coordinate transforming means to prepare
drawing data of at least one second bird's-eye view to be obtained
through the perspective projection using a second projection angle
which is smaller than a first projection angle corresponding to the
projection angle to obtain a first bird's-eye view, and instructing
said image display device to display a map image with the drawing
data of the second bird's-eye view between the first bird's-eye
view display obtained through the perspective projection using the
first projection angle and the plan view display, in a case where a
display target for which the drawing data are to be prepared is
changed from one of the first bird's-eye view and the plan view to
the other.
8. The map display apparatus as claimed in claim 7, wherein said
projection angle changing means includes means for preparing
drawing data of two or more said second bird's-eye views by using
two or more said second projection angles which 5 are different
from each other, wherein when the display target is changed from
the bird's-eye view to the plan view, said projection angle
changing means successively displays the two or more second
bird's-eye views in a projection-angle order from a larger
projection angle to a smaller projection angle, and when the
display target is changed from the plan view to the bird's eye
view, said projection angle changing means successively displays
the two or more second bird's-eye view in a projection-angle order
from a smaller projection angle to a larger projection angle.
9. The map display apparatus as claimed in claim 6, wherein said
map drawing means further includes means for accepting an
indication of any point contained in the map data through said
input device, and wherein said drawing determining means determines
the drawing data of the plan view as the drawing data to be
prepared when accepting the indication of the point.
10. The map display apparatus as claimed in claim 1, wherein the
map data contain, as character string data, vector data to
recognize the position of a character string, and image data to
recognize an image of the character string, and said coordinate
transforming means performs no perspective projection on the image
data of the map data.
11. The map display apparatus as claimed in claim 1, wherein said
map drawing means further includes drawing judgment means for
determining whether data of at least one node contained in the
drawing data should be set as one of a number of drawing targets,
and eliminating said data of a node which is not set as a drawing
target from the drawing targets, and wherein said map drawing means
displays a map image on said image display device with the drawing
data which have been processed by said drawing judgment means.
12. The map display apparatus as claimed in claim 11, wherein when
the data of the node are data of a character string, the judgment
of said drawing judgment means is based on a judgment as to whether
the display height of the character string from the bottom side of
a display frame after the perspective projection is equal to or
less than a predetermined reference value on the display frame.
13. The map display apparatus as claimed in claim 12, wherein the
reference value is equal to "2/3" from the bottom side of the
display frame when the display height (size) of the display frame
is set to "1".
14. The map display apparatus as claimed in claim 11, wherein when
the data of the node are data of a character string, the judgment
of said drawing judgment means is based on a judgment as to whether
the distance between the visual-point position and the position at
which the character string is defined in the map data is equal to
or less than a predetermined reference value.
15. The map display apparatus as claimed in claim 11, wherein when
the data of the node are data of a character string, the judgment
of said drawing judgment means is based on a judgment as to whether
the distance between a predetermined point contained in the map and
the position at which the character string is defined in the map
data is equal to or less than a predetermined reference value.
16. The map display apparatus as claimed in claim 11, wherein an
attribute is beforehand allocated to at least a part of each node,
and said drawing judgment means sets, as a drawing target, data of
a node having an attribute which meets a preset attribute allocated
to each display area on the display frame, and eliminates from the
drawing targets data of a node having an attribute which does not
meet the preset attribute.
17. The map display apparatus as claimed in claim 1, wherein said
coordinate transforming means changes the projection angle in
accordance with the distance between two predetermined points
contained in the map data.
18. The map display apparatus as claimed in claim 17, wherein said
coordinate transforming means reduces the projection angle to a
smaller value as the distance between the two points becomes
shorter.
19. The map display apparatus as claimed in claim 1, wherein the
map data contain data of character strings, and said map drawing
means further includes means for setting a display priority rank
for the character strings, and character string rearranging means
for displaying a character string having the highest display
priority rank of character strings when the display positions of
said character strings are overlapped with one another.
20. The map display apparatus as claimed in claim 19, wherein the
display priority rank of a character string is set in accordance
with the display height of the character string on the display
frame from the bottom side of the display frame.
21. The map display apparatus as claimed in claim 20, wherein the
display priority rank of a character string is set to be higher as
the display height of the character string on the display frame
from the bottom side of the display frame becomes lower.
22. The map display apparatus as claimed in claim 19, wherein the
display priority rank of a character string is set in accordance
with the distance between a predetermined point contained in the
map data and a point at which the character string is defined.
23. The map display apparatus as claimed in claim 22, wherein the
display priority rank is set to be higher as the distance between
the predetermined point and the point at which the character string
is defined becomes shorter.
24. A map display apparatus comprising an image display device, map
storing means for storing map data to display a map, and map
drawing means for preparing drawing data of said map by using said
map data read out from said map storing means and displaying a map
image on said image display device on the basis of the drawing
data, wherein the map data contain data of character strings, and
wherein said map drawing means includes means for setting display
priority ranks of the character strings, and character rearranging
means for displaying a character string having the highest display
priority rank of overlapped character strings when the display
positions of said character strings are overlapped with one another
on a display map.
25. A navigation system comprising an image display device, map
storing means for storing map data to display a map, map drawing
means for preparing drawing data of said map by using said map data
read out from said map storing means and displaying a map image on
said image display device on the basis of the drawing data, and
current position recognizing means for recognizing a current
position, wherein said map drawing means includes coordinate
transforming means for transforming coordinate data contained in
the map data, and said coordinate transforming means includes
perspective projection means for perspectively projecting the
coordinate data contained in the map data onto a predetermined
projection plane with a view point at a desired position, to
thereby prepare the drawing data of a bird's-eye view.
26. The navigation system as claimed in claim 25, further
comprising an input device, wherein said coordinate transforming
means further includes means for accepting an input of the position
of the view point through said input device, and means for
determining the projection plane on the basis of predetermined two
points contained in the map data and the input view point position
so that the drawing positions of the two points after the
perspectively projecting operation are coincident with
predetermined positions.
27. The navigation system as claimed in claim 26, wherein one of
said two points is the current position which is recognized by said
current position recognizing means.
28. The navigation system as claimed in claim 25, further
comprising an input device, wherein said coordinate transforming
means further includes means for accepting an input of a scale
through said input device, and means for determining the position
of the view point and the projection plane on the basis of the
coordinates of predetermined two points contained in the map data
and the input scale so that the drawing positions of the two points
after the perspectively projecting operation are coincident with
predetermined positions, and the scale of a drawn map on the
projection plane is coincident with the input scale.
29. The navigation system as claimed in claim 28, wherein one of
the two points is the current position which is recognized by said
current position recognizing means.
30. The navigation system as claimed in claim 25, further
comprising an input device, wherein said coordinate transforming
means changes the projection angle in accordance with the distance
between the current position recognized by said current position
recognizing means and a destination which is indicated through said
input device.
31. The navigation system as claimed in claim 25, wherein the map
data contain data of a character string, and said map drawing means
further includes drawing judgment means for judging whether said
data of said character string contained in the drawing data should
be set as one of a number of drawing targets, on the basis of the
distance between a point at which the character string is defined
in the map data and a point on the map data which corresponds to
the current position recognized by said current position
recognizing means, and eliminating said data of the character
string which are judged not to be set as a drawing target from the
drawing targets, and wherein said map drawing means displays a map
image on said image display device on the basis of the drawing data
which have been processed by said drawing judgment means.
32. The navigation system as claimed in claim 25, wherein the map
data contain data of a character string, and said map drawing means
further includes means for setting display priority ranks for each
said character strings, and character string rearranging means for
displaying said character string having the highest display
priority rank of overlapped character strings when the display
positions of character strings are overlapped with one another on
the display frame, and wherein the display priority rank of said
character string is set in accordance with the distance between a
point on the map which corresponds to the current position
recognized by said current position recognizing means and the point
at which the character string is defined.
33. The navigation system as claimed in claim 25, wherein said
coordinate transforming means further includes means for
determining the view point or the projection angle and the
projection plane so that a height of a display position of the
current position recognized by said current position recognizing
means from a bottom side of a display frame is equal to or less
than "1/3" when the height of the display frame is set to "1".
34. A bird's-eye view forming method for preparing drawing data of
a map represented in a bird's-eye view display mode with map data,
characterized in that coordinate data contained in the map data are
perspectively projected onto a predetermined projection plane with
a view point at a desired position to thereby prepare the drawing
data of a bird's-eye view.
35. The bird's-eye view forming method as claimed in claim 34,
comprising the steps of: accepting an input of the position of the
view point; and determining the projection plane on the basis of
the coordinates of predetermined two points contained in the map
data and the input position of the view point so that the drawing
positions of the two points after the perspective projection are
coincident to predetermined positions.
36. The method as claimed in claim 34, comprising the steps of:
accepting an input of a scale; and determining the position of the
view point and the projection plane on the basis of the coordinates
of predetermined two points contained in the map data and the input
scale so that the drawing positions of the two points after the
perspective projection are coincident with predetermined positions,
and the scale of a drawn map on the projection plane is coincident
with the input scale.
37. The method as claimed in claim 34, comprising the steps of:
accepting an input of a projection angle which is an intersection
angle between the projection plane and a plane on which the map
data are defined; and determining the projection plane on the basis
of the input projection angle and a position of the view point.
Description
BACKGROUND OF THE INVENTION
[0001] 1 Field of the Invention
[0002] The present invention relates to a navigation system for
detecting the position of a moving body to inform a user of the
current position of the moving body, and a map display apparatus
using the navigation system.
[0003] 2. Description of Related Art
[0004] Various types of navigation systems have been recently
known, and these navigation systems are used while mounted on
moving bodies such as vehicles, ships, etc. When such a navigation
system is mounted on a moving body, it performs arithmetic and
logic processing on information provided from various sensors to
detect the current position of the moving body and display the
current position on a screen of the navigation system.
[0005] This type of navigation system includes a position detector
for detecting the absolute position of the moving body, a storage
device for storing map data which include two-dimensional vector
data obtained by projecting roads and points on the ground, such as
structures, etc., onto a mesh-segmented plane using a universal
transverse Mercator projection method, and character data
associated with the vector data, an input device for receiving
external instructions (commands), and a display device for reading
out desired vector data from the mesh-segmented map stored in the
storage device in accordance with an instruction input from the
input device, to perform data conversion processing on the data,
and then displaying the map on the display.
[0006] The data conversion processing includes shift conversion
processing for changing the display position on a map, scale
conversion (enlarging/reducing) processing for displaying a map on
any scale, and rotational coordinate-transformation processing for
changing a display direction on the map. With these processings, a
plan view map is obtained by drawing the ground through an
orthogonal projection in a vertical direction.
[0007] As described above, when a map is displayed on the screen,
the conventional navigation system as described above adopts a
plan-map display mode in which the ground is drawn in the vertical
orthogonal projection style. Therefore, in order to simultaneously
display two spots which are far away from each other, a
reduction-scale of the map must be necessarily increased, and thus
detailed information cannot be displayed on the screen.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a
bird's-eye view forming method for displaying a map of a plane
(ground) on the basis of a bird's-eye view corresponding to a
projected plan of the plane (ground) which is obtained by
projecting the plane (ground) on any plane between the plane
(ground) and a view point when the plane (ground) is viewed from
the view point located at any height from the plane (ground), a map
display apparatus using the bird's-eye view forming method, and a
navigation system using the map display apparatus.
[0009] In order to attain the above object, a bird's-eye view
forming method for forming, from map data, drawing (display) data
for a map which is to be represented by a bird's-eye view, is
characterized in that coordinate data contained in the map data are
perspectively converted to drawing (display) data based on a
bird's-eye view on a desired projection plane with a view point
being set to a desired position (i.e., the coordinate data of the
map data on a vertical orthogonal projection plane are
perspectively converted to drawing (display) data on a desired
projection plane based on a bird's-eye view).
[0010] The bird's-eye view forming method preferably includes a
step of receiving an input of the position of the view point, and a
step of determining the projection plane so that the drawing
(display) positions of two predetermined spots (for example, a
current position and a destination) which are obtained through a
perspectively projecting transformation on the basis of the
coordinates of the two spots in the map data and the position of
the view point, are set to predetermined positions. (Here, the
perspectively projecting conversion is defined as such a data
conversion that data on a plan view are converted to data on a
bird's-eye view through a perspective projection operation.
Therefore, by using the perspectively projecting conversion, a
plan-view map is converted to a bird's-eye view map. In the
following description, the perspectively projecting conversion is
merely referred to as "perspective projection").
[0011] Alternatively, the bird's-eye view forming method may
include a step of receiving an input of a scale, and a step of
determining the position of the view point and the projection plane
so that the drawing (display) positions of the two predetermined
spots (for example, a current position and a destination) which are
obtained by performing the perspective projection on the basis of
the coordinates of the two spots in the map data and the input
scale, are set to predetermined positions, and a scale of a drawn
(displayed) map is equal to the input scale.
[0012] Further, the bird's-eye view forming method may include a
step of receiving an input of a projection angle which is defined
as an angle at which a plane defined for the map data and the
projection plane intersect each other, and a step of determining
the projection plane on the basis of the input projection angle and
the set view point position.
[0013] Still further, according to the present invention, there are
provided a map display apparatus for displaying a bird's-eye view
by using the bird's-eye view forming method as described above, and
a navigation system for displaying a map by using the map display
apparatus.
[0014] According to the bird's-eye view display apparatus and the
navigation system, map drawing means includes coordinate
transforming means, and the coordinate transforming means performs
the perspective projection (conversion) on the map data to convert
a plan-view map to a bird's-eye view map, and to display the
converted map on a screen. Therefore, according to the present
invention, a user can obtain a bird's-eye view display which is
easy to see and in which the user can easily recognize the
positional relationship of spots displayed on the map. According to
the bird's-eye view forming method of the present invention, the
view point can be freely set, so that it can meet user's need.
[0015] According to the present invention, a navigation system
which is excellent in operational performance and convenient for a
user can be obtained if it is designed to overcome the following
first to seventh problems.
[0016] Firstly, in the case where the processing speed of scroll
processing in a bird's-eye view display mode is lower than that in
a plan display mode, the operational performance may be degraded
when the scroll processing is frequently used to search for a
desired spot on the bird's-eye view display (first problem).
[0017] Therefore, it is preferable in the present invention that
the plan view (plan map) display mode and the bird's-eye view
display mode are freely switchable. With this switching operation,
both the plan view display and the bird's-eye view display can be
made in accordance with a user's requirement, and thus the
convenience is enhanced.
[0018] In the above case, a second problem occurs, namely, that it
is difficult for the user to grasp the positional relationship
between two different type of view when display is switched between
the plan view display and the bird's-eye view display. This is
because the position of the same spot to be displayed on the screen
varies significantly due to variation of the view point with
respect to the map, when the display switching operation is
performed, and further, spots which have not been displayed or have
been displayed until the display switching time are respectively
displayed or are not displayed at the display switching time.
[0019] Therefore, if the present invention is designed so that the
display is freely switchable the plan view display and the
bird's-eye view display, it is further preferable that an
intersecting angle between a plane containing the map data and a
plane onto which the map is projected, is gradually increased or
reduced in time series. That is, according to the present
invention, it is preferable that the view point is smoothly shifted
during the conversion between the plan view display and the
bird's-eye view display. With this operation, the shift between the
plan view and the bird's-eye view is smoothly performed, and thus
the user can easily recognize the positional relationship between
spots displayed on the plan view map and the same spots displayed
on the bird's-eye view map.
[0020] Thirdly, when the map is displayed in the bird's-eye view
display mode, if the view point serving as a parameter to the
perspective projection is fixed to a position, a mark indicating
the current position which is displayed on the screen is shifted on
the map while the current position is shifted. In this case, if the
marked current position deviates from a displayed map area, the
mark of the current position is not displayed (third problem).
[0021] Therefore, according to the present invention, the view
point from which to obtain the bird's-eye view may be fixed to a
specific position which is set to be away from the current position
at a fixed distance and in a fixed direction at all times.
Furthermore, the height of the view point may be varied in
accordance with an external operation. If the view point is fixed
to the specific position as described above, the bird's-eye view is
displayed such that the current position is fixed to a point on the
screen at all times, so that the user can easily grasp the current
position. Furthermore, if the position of the view point can be set
to a user's desired position, the convenience can be further
enhanced.
[0022] Fourthly, when two spots are displayed on the same frame, it
is sufficient in the conventional plan view display to renew the
scale in accordance with the distance between the two points.
However, in the bird's-eye view display of the map, the map cannot
be optimally displayed by merely renewing the scale (fourth
problem).
[0023] Therefore, according to the present invention, an
instruction regarding the positions of two spots (for example, the
current position and the destination) may be accepted, and the view
point and the intersection angle between the map-projected plane
(bird's-eye view) and the plane containing the map data (plan view)
may be determined so that the two spots are displayed at
predetermined positions on the screen, whereby the bird's-eye view
display is performed. With this operation, the positional
relationship between the two spots can be easily recognized.
Further, even when the positions of the two spots vary, these are
displayed on the same frame at all times, so that the user can
grasp the positional relationship between the two spots with no
complicated operation.
[0024] According to the present invention, in the bird's-eye view
display mode, line backgrounds such as roads, railroad lines, etc.,
plane backgrounds such as rivers, green zones, etc., and character
strings may be perspectively converted and drawn on the bird's-eye
view map. However, if the character strings are perspectively
converted, the shape of a character is smaller and is more deformed
as it becomes farther away from the view point. On the other hand,
if it is in the vicinity of the view point, it is enlarged. Thus
the character strings may be illegible in these cases (fifth
problem).
[0025] Therefore, it is preferable that the coordinate transforming
means of the present invention does not perform the perspective
projection on a character image. In this case, characters contained
in the bird's-eye view are displayed at the same size, so that the
character strings are easily legible.
[0026] Further, when a lot of character data are displayed,
character strings are displayed while overlapping with one another.
Particularly in the bird's-eye view, an angle of depression with
respect to the view point is smaller at a far-distance point from
the view point and thus the reduction scale is large at that point,
so that the data amount of character data to be displayed per unit
area is increased. Accordingly, the character data (strings) are
liable to be overlapped with each other at the far-distance point
(sixth problem).
[0027] Therefore, it is preferable that as the position of
character data contained in the map data becomes nearer to the view
point, drawing (display) judgment means of the present invention
displays the character data more preferentially (i.e., increases
the display priority rank of the character data). With this
operation, character data having a higher display priority rank may
be displayed while being superposed on character data having a
lower display priority rank, so that the character string can be
prevented from being deficient and it can be made legible.
[0028] When the current position is located in the vicinity of the
bottom side of the display frame or the view point, it is
preferable that the display height or the distance from the view
point is set as a criterion for determining the display priority
rank. Further, when two or more character strings are displayed
while overlapping with one another, a character string which is
displayed at a lower display height (which is the height from the
bottom side of the display frame) on the screen may be displayed
more preferentially (i.e., so that the character string is not
covered by the other character strings, but is superposed on the
other character strings). In this case, the character data near to
the current position are displayed while being prevented from being
covered by the other character strings and thus missed. With this
display operation, the deficiency (missing) of the character
information (string) near to the current position which the user
has a greater need for can be prevented, and the character string
can be made legible.
[0029] As described above, when the bird's-eye view display is
performed, the data amount of line data, plane background data and
character data to be drawn per unit area is increased in a region
which is far away from the view point (hereinafter referred to as
"far-distance region", and this region is a region having a small
angle of depression). Accordingly, when the character data of these
data are drawn while superposed on the other data, the line data
and the plane background data are covered by the character data in
the far-distance region, so that it may be difficult to check the
shapes of roads, etc. in the far-distance region (seventh
problem).
[0030] Therefore, the drawing judgment means of the present
invention preferably eliminates, from targets to be drawn
(displayed), those character strings which are obtained through the
perspective projection of the map and which are located at
positions higher than a predetermined display height from the
bottom side of the display frame. Or the drawing judgement means
may eliminate those character strings which are defined at position
where is further than a fixed distance from the view point. As
described above, the character strings are not displayed (drawn) in
a region which is located above the predetermined height or is more
than at a predetermined distance away, that is, in a region-where
the data amount to be drawn per unit area is considerably increased
due to the reduction in angle of depression in the bird's-eye view
display mode. Therefore, a road display, a plane background
display, etc. are not covered by the character string display, so
that the recognition of roads in the far-distance regions can be
prevented from being impaired even in the bird's-eye view display
mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a diagram showing an example of a bird's-eye view
display drawn (displayed) according to the present invention;
[0032] FIG. 2 is a diagram showing a navigation system of an
embodiment according to the present invention;
[0033] FIG. 3 is a block diagram showing a hardware construction of
a processing unit;
[0034] FIG. 4 is a functional block diagram showing the processing
unit;
[0035] FIG. 5 is a functional block diagram showing map drawing
means;
[0036] FIG. 6 is a diagram showing a perspective projection
processing of a map;
[0037] FIG. 7 is a diagram showing a series of coordinate
transforming steps for bird's-eye view display;
[0038] FIG. 8 is a flowchart for a processing flow of the
coordinate transforming means;
[0039] FIGS. 9A, 9B and 9C are diagrams showing a setting method of
a view point and a projection plane for bird's-eye view
display;
[0040] FIGS. 10A, 10B and 10C are diagrams showing a setting method
of a view point and a projection plane for bird's-eye view
display;
[0041] FIG. 11 is a flowchart for a flow of the perspective
projection processing;
[0042] FIG. 12 is a flowchart showing a processing flow of drawing
(display) judgment means;
[0043] FIGS. 13A and 13B are diagrams showing an effect of a
rearrangement operation of character strings;
[0044] FIGS. 14A and 14B are diagrams showing an effect of a
drawing (display) character string selecting operation;
[0045] FIGS. 15A, 15B and 15C are diagrams showing a setting method
of a view point and a projection plane for bird's-eye view
display;
[0046] FIGS. 16A, 16B and 16C are diagrams showing a setting method
of a view point and a projection plane for bird's-eye view display;
and
[0047] FIG. 17 is a perspective view showing the outlook of the
navigation system of the embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] A preferred embodiment according to the present invention
will be described with the accompanying drawings. In the following
embodiment, the navigation system is mounted on a vehicle such as a
car or the like, but, the same effect can be obtained when the
navigation system is mounted on other moving bodies such as a ship,
a train, etc.
[0049] FIG. 1 shows a bird's-eye view which is displayed by a
bird's-eye view map display apparatus installed in a navigation
system of an embodiment according to the present invention. The
bird's-eye view map display apparatus of this embodiment forms a
bird's-eye view showing a landscape obtained through a bird's eye
as a projection drawing of two-dimensional map data (represented by
reference numeral 101 in FIG. 1), and displays it on a display
screen of a display. Here, the bird's-eye view is defined as a view
of a landscape which is obtained as if it is viewed through the
eyes of a bird flying at a specific position which is high above
the ground.
[0050] In FIG. 1, reference numeral 102 represents a bird's-eye
view. In the bird's-eye view 102, a route 104 which is emphatically
displayed to indicate a travel course (the emphasis is made with a
bold line as shown in FIG. 1, but, it may be made using flashing
display or discoloration), and reference numeral 105 represents a
mark (symbol) indicating the current position. In FIG. 1, arrows
(indicated by solid lines and dotted lines) represent a projection
from the two-dimensional map data 101 to the bird's-eye view
102.
[0051] FIG. 17 is a perspective view showing the outlook of the
navigation system for a vehicle according to the embodiment. The
navigation system of this embodiment is installed in a housing 69,
and the housing 69 is equipped with a display screen of the display
2, a scroll key unit 66, a scale changing key unit 67, a projection
angle changing key unit 68, a touch panel 70 provided on the
display screen of the display 2, etc.
[0052] The scroll key unit 66 is responsive to a scroll instruction
of an image displayed on the display screen, and has four
direction-instruction keys 660 which are responsive to shift-up,
shift-down, shift-to-right, shift-to-left instructions,
respectively. The scale changing key unit 67 is responsive to an
instruction of changing the scale of a map displayed on the screen,
and has two scale instructing keys 67a and 67b which are responsive
to scale-up and scale-down instructions, respectively. The
projection angle changing key unit 68 is responsive to an
instruction to change the angle of a projection plane of a
bird's-eye view to be displayed on the screen, and has two angle
instruction keys 68a and 68b which are responsive to
projection-angle increasing and decreasing instructions,
respectively. The touch panel 70 serves as an input means which
detects a touch (contact) to the surface thereof to output a
touched position on the surface thereof. The keys 66 to 68 may be
designed as a software key which is triggered through the touch to
a predetermined region on the touch panel 70.
[0053] As shown in FIG. 2, the navigation system for a vehicle
according to this embodiment includes a processing unit 1, a
display 2 which is connected to the processing unit 1 through a
signal line S1, a map storage device 3 which is-connected to the
processing unit 1 through a signal line S2, a voice input/output
device 4 which is connected to the processing unit 1 through a
signal line S3, an input device 5 which is connected to the
processing unit 1 through a signal line S4, a wheel speed sensor 6
which is connected to the processing unit 1 through a signal line
S5, an attitude (geomagnetic) sensor 7 which is connected to the
processing unit 1 through a signal line S6, a gyro 8 which is
connected to the processing unit 1 through a signal line S7, a GPS
(Global Positioning System) receiver 9 which is connected to the
processing unit 1 through a signal line S8, and a traffic
information receiver 10 which is connected to the processing unit 1
through a signal line S9. Each of the signal lines S1 to S9, may be
either wire type or wireless type is used insofar as these types of
signal lines can transmit signals. In this embodiment, the wire
type is used.
[0054] The processing unit 1 is a central unit for performing
various processing. For example, it detects the current position on
the basis of information output from the various sensors 6 to 9,
and reads desired map information from the map storage device 3 on
the basis of the obtained current position information. In
addition, it graphically develops map data to display the map data
while overlapped with a current-position mark, and selects the
optimum road which connects the current position and a destination
instructed by the user to inform the user of the optimum course
with voice or graphic display.
[0055] The display 2 serves to display graphic information
generated in the processing unit 1, and it comprises a CRT or a
liquid crystal display. RGB (Red, Green, Blue) signals or NTSC
(National Television System Committee) signals are normally
transmitted along the signal line S1 between the processing unit 1
and the display 2, like a normal system.
[0056] The map storage device 3 includes a large-capacity storage
medium such as a CD-ROM (Compact Disk-Read Only Memory) or IC
(Integrated Circuit) card, and it performs a read-out operation of
reading out data held in the large-capacity storage medium in
response to an instruction of the processing unit 1 to supply the
data to the processing unit 1, and a write-in operation of writing
data supplied from the processing unit 1 into the large-capacity
storage medium.
[0057] The voice input/output device 4 serves to convert a message
produced in the processing unit 1 to a voice message to a user, and
it also serves to receive a voice input and recognize the content
thereof and to transmit the information to the processing unit
1.
[0058] The input device 5 serves to receive an instruction input
externally, and it includes the scroll key unit 66, the scale
changing key unit 67, the projection angle changing key unit 68 and
the touch panel 70 in this embodiment. The input device 5 of the
present invention is not limited to the above construction, and
another input means such as a joy stick, a keyboard, a mouse, a pen
input device or the like may be used.
[0059] The navigation system of this embodiment has various sensors
such as a wheel speed sensor 6 for measuring the distance on the
basis of the product of the circumferential length of the wheels of
a vehicle and the detected number of rotations of the wheels, and
measuring a turn angle of the vehicle on the basis of the
difference in number of rotations between the paired wheels, an
attitude (geomagnetic) sensor 7 for detecting the earth's magnetic
field to measure a direction in which the vehicle is oriented, a
gyro 8 such as an optical fiber gyro, a vibrational gyro or the
like for measuring a rotational angle of the vehicle, and a GPS
receiver 9 for receiving signals from three or more GPS satellites
to measure the distance between the vehicle and each of the GPS
satellites, and variation of the distance, thereby measuring the
current position, the travel direction and the travel azimuth
(bearing) of the vehicle. The sensors of the present invention are
not limited to the above sensors. For example, in a navigation
system mounted in a ship, a Doppler sonar is used to detect the
speed of the ship, and any sensor may be suitably selected in
accordance with its use purpose.
[0060] Further, the navigation system of this embodiment has a
traffic information receiver 10 to receive signals from beacon
transmitters or FM (Frequency Modulation) broadcasting stations
which transmit traffic information such as information on traffic
jams, road repairs and suspension of traffic, and information on
parking areas.
[0061] FIG. 3 shows the hardware construction of the processing
unit 1 as described above. The processing unit 1 includes a CPU
(Central Processing unit) 21 for performing a numerical operation
and a control operation of the devices 22 to 31, a RAM (Random
Access Memory) 22 for holding maps and processing data, a ROM (Read
Only Memory) 23 for holding programs, a DMA (Direct Memory Access)
24 for performing data transmission between memories and between
memories and respective devices at high speed, a drawing controller
25 for performing a graphics drawing operation when developing
vector data to an image at high speed and performing a display
control, a VRAM (Video Random Access Memory) 26 for storing graphic
image data, a color pallet 27 for converting the image data to RGB
signals, an A/D (Analog/Digital) converter 28 for converting analog
signals to digital signals, an SCI (Serial Communication Interface)
29 for converting serial signals to parallel signals which are
synchronized with a bus, an I/O (Input/Output) device 30 for
synchronizing serial signals with parallel signals, then sending
the synchronized serial signals into the bus, and a counter 31 for
integrating a pulse signal. These devices 21 to 31 are connected to
one another through the bus.
[0062] Next, the functional construction of the processing unit 1
will be described with reference to FIG. 4.
[0063] The processing unit 1 includes user's operation analyzing
means 41, route calculating means 42, route guiding means 43, map
drawing means 44, current position calculating means 45, map match
processing means 46, data read-in processing means 47, menu drawing
means 48, and graphics processing means 49 as shown in FIG. 4. In
this embodiment, each of these means 41 to 49 is implemented
through execution of instructions stored in the ROM 23 by the CPU
21. However, the present invention is not limited to the above
implementation, and each of the means may be implemented using a
hardware construction such as a dedicated circuit or the like.
[0064] The current position calculating means 45 serves to
time-integrate distance data and angle data which are obtained by
integrating distance pulse data measured by the wheel speed sensor
6 and angular velocity data measured by the gyro 8, to calculate
the current position (X', Y') of a vehicle after travel on the
basis of an initial position (X, Y). Here, the current position
calculating means 45 corrects the absolute azimuth of the vehicle
travel direction on the basis of the azimuth data obtained by the
attitude sensor 7 and the angle data obtained by the gyro 8 so that
an angle by which the vehicle has been rotated is matched with a
vehicle travel azimuth. When the data obtained by the sensors are
integrated as described above, errors of the sensors are
accumulated. Therefore, the current position calculating means 45
also performs correction processing so that the accumulated errors
are canceled on the basis of positional data obtained by the GPS
receiver 9 at a predetermined time interval (every one second in
this embodiment) to output the corrected data as current position
information.
[0065] As described above, the current position information thus
obtained still contains minute errors due to the sensors.
Therefore, in,order to enhance the positional precision of the
navigation system, a map match processing is performed by the map
match processing means 46. In this processing, data of roads
contained in a map around the current position which are read in by
the data read-in processing means 47 are compared with a travel
locus obtained by the current position calculating means 45 to
match the current position to a road which has the highest
correlation in shape. In many cases, the current position can be
matched to the travel road through the map match processing, so
that the current position information can be output with high
precision.
[0066] The user's operation analyzing means 41 analyzes a user's
demand or instruction which is input through the input device 5 by
the user, and controls the units 42 to 48 to perform the processing
corresponding to the demand (instruction). For example, when a
demand for route guidance to a destination is input, the user's
operation analyzing means 41 instructs the map drawing means 44 to
display a map to set the destination, and then instructs the route
calculation means 42 to determine a route extending from the
current position to the destination and instructs the route guide
means 43 to supply the route guidance information to the user.
[0067] The route calculation means 42 searches a node connecting
two specified points by using a Dijkistra method or the like to
obtain a route having the highest priority. The route calculating
means 42 has plural criteria for the priority order, and it uses a
criterion indicated by a user's instruction to determine the route.
In this embodiment, in accordance with the instruction, there can
be obtained a route providing the shortest distance between the two
points, a route along which the vehicle can reach to the
destination in the shortest time, a route in which cost is
cheapest, or the like.
[0068] The route guide means 43 compares link information of a
guide route obtained by the route calculating means 42 with the
current position information obtained by the current position
calculating means 45 and the map match processing means 46. Before
passing through a crossing or the like, it outputs
direction-instructing information to the voice input/output device
4 indicating whether the vehicle should go straight, or whether the
vehicle should turn to the right or left, whereby the information
is output as a voice message, or a direction in which the vehicle
should travel is drawn on a map displayed on the screen of the
display 2.
[0069] The data read-in processing unit 47 operates to prepare for
the read-in operation of map data of a desired region from the map
storage device 3. The map drawing means 44 receives from the data
read-in processing means 47 the map data around a position for
which the display is instructed, and it operates to transmit to the
graphics processing means 49 a command for drawing specified
objects on a specified reduction-scale with a specified direction
set to an up-direction.
[0070] The menu drawing means 48 receives a command output from the
user's operation analyzing means 41, and transmits to the graphics
processing means 49 a command for drawing demanded various
menus.
[0071] The graphics processing means 49 receives drawing commands
generated by the map drawing means 44 and the menu drawing means 48
to develop an image in the VRAM 26.
[0072] Next, the function of the map drawing means 44 will be
described with reference to FIG. 5 the map drawing means 44
includes initial data clip means 61, coordinate transforming means
62, drawing judgment means 63, data clip means 64 and drawing
command issuing means 65.
[0073] The initial data clip means 61 performs clip processing to
select road data, plane and line background data and character data
on a region, which are required for subsequent processing, from
each mesh of map data read out from the map storage device 3 by the
data read-in processing means 47, and supplies the selection result
to the coordinate transforming means 62. In this embodiment, the
initial data clip means 61 is actuated at a time interval (period)
for renewing drawn map (for example 0.5 seconds) or it is actuated
in accordance with an instruction from the user's operation
analyzing means 41.
[0074] As algorithms for the clip processing Cohen-Sutherland line
clip algorithm for the road data and the line data,
Sutherland-Hodgman polygon clip algorithm for the plane data, etc.
are used, (Foley, van Dam, Feiner, Hughes: Computer Graphics:
Addison-Wesley Publishing Company pp. 111-127). With this
processing, the amount of data which will be subsequently subjected
to the coordinate projection or the drawing processing can be
reduced, so that the processing speed is expected to be higher.
[0075] The coordinate transforming means 62 performs processing for
transforming each coordinate value of the map data obtained in the
clip processing, such as enlargement/reduction processing, rotation
processing and projection processing of the map data. The
coordinate transforming means 62 is actuated in accordance with an
instruction from the initial data clip means 61 or the user's
operation analyzing means 41.
[0076] The drawing judgement means 63 operates to select those data
which are contained in the map data obtained by the coordinate
transforming means 62 and actually required to be drawn. For
example, when the reduction-scale is large, the drawing judgment
means 63 operates to omit narrow roads or omissible place names
because of the substantial increase in the amount of data to be
drawn. With this operation, the processing speed for the drawing
can be prevented from being significantly reduced. The drawing
judgment means 63 is actuated in accordance with an instruction
from the coordinate transforming means 62 or the user's operation
analyzing means 41.
[0077] The data clip means 64 operates to select the map data on
the drawing region from the map data obtained by the drawing
judgment means 63 through the clip processing. The same algorithms
as the initial data clip means may be used by the data clip means
64. The data clip means 64 is actuated in accordance with an
instruction from the drawing judgment means 63 or the user's
operation analyzing means 41. The data clip means 64 may be
omitted.
[0078] The drawing command issuing means 65 operates to issue to
the graphics processing unit 49 commands for drawing lines,
polygons, characters, etc. and commands for setting patterns to
drawn roads, planes, lines, background data, character data, etc.
with indicated colors or patterns. The drawing command issuing
means 65 is actuated in accordance with an instruction from the
data clip means 64.
[0079] In this embodiment, the initial data clip means 61 is
actuated at a time interval (period) for renewing a drawn map (for
example, every 0.5 seconds), and it transmits the data obtained in
the clip processing to the coordinate transforming means 62.
Accordingly, according to this embodiment, the drawing operation is
performed every 0.5 seconds except for a case where an instruction
is supplied from an external operation.
[0080] Next, the outline of the bird's-eye view display will be
described with reference to FIG. 6.
[0081] When a map is displayed, a printed map table or a
conventional navigation system provides a plan-view map display in
which the ground is viewed from an infinite point. The plan-view
map display has an advantage that the scale is fixed over any
position on the same display frame, so that the user can easily get
the sense of distance. However, when two points are required to be
displayed on the same display frame, it is necessary to perform an
adjustment operation of optimizing the scale. In addition, when the
two points are far away from each other, only limited information
is displayed because the information amount to be displayed at the
same time is restricted by the size and precision of the display.
This problem can be avoided by using the bird's-eye view
display.
[0082] The bird's-eye view display can be achieved by the
perspective projection processing in which two-dimensional or
three-dimensional map information 53 of a plane A is projected onto
a plane B intersecting the plane A at an angle .theta., to thereby
obtain projection information 54.
[0083] In the schematic diagram of FIG. 6, a point 55 of coordinate
(Tx, Ty, Tz) is set as a view point, and a map 53 (represented by a
rectangle having vertexes a, b, c and d) on the plane A
(illustrated by a rectangle 51 ) is projected onto the plane B
(illustrated by a rectangle 52 ) which intersects the plane A at an
angle .theta., to obtain a projection 54 (represented by a
rectangle having vertexes a', b', c' and d'). The points a, b, c
and d of the map 53 are projected to the points a', b', c' and d'.
In this specification, the view point 55 which is the origin of a
visual-point coordinate system in the projection processing is
merely referred to as "view point". Further, in this specification,
the term "view point" does not mean a view point corresponding to
the position of the user's eyes.
[0084] In the bird's-eye view display, information close to the
view point 55 (for example, line ab) is enlarged, and information
which is far away from the view point (for example, line cd) is
reduced. Accordingly, when two points are displayed on the same
display frame, these points are displayed so that one point for
which more detailed information is desired is located near to the
view point, while the other point is located far away from the view
point. In this case, the positional relationship (interval
distance, etc.) between the two points can be easily recognized,
and a large amount of information on the periphery of the view
point can be provided to the user.
[0085] According to this embodiment, since two-dimensional map data
are usable as map information for the bird's-eye view display, the
bird's-eye view display can be realized in the conventional
navigation system with no additional new map data, by adding means
for performing the perspective projection processing as described
above. In this embodiment, the perspective projection processing is
performed by the coordinate transforming means 62. Further, it is
preferable to use various means of implementation as described
later, when the bird's-eye view display is performed.
[0086] First, a basic method of realizing the bird's-eye view
display will be described with reference to FIG. 7.
[0087] The coordinate transforming means 62 sets the position of
the view point, and determines a viewing direction from the view
point and a projection angle (an angle .theta. at which the
projection plane B intersects to the plane A in the case of FIG. 6)
(step 1). In this step, a region which is to be displayed in the
bird's-eye view mode is determined. When a bird's-eye view is
displayed on a rectangular display frame (screen), a near-distance
region which is close to the view point is narrowed, and a
far-distance region which is far away from the view point is
broadened. Therefore, map data to be finally drawn becomes a
trapezoidal region 72 in a map mesh 71.
[0088] Next, the coordinate transforming means 62 uses the initial
data clip means 61 to extract map data of a circumscribed
rectangular region 73 of the trapezoidal region 72 to be actually
drawn, from map mesh data 71 containing the region to be displayed
in the bird's-eye view mode (step 2).
[0089] Subsequently, the coordinate transforming means 62 enlarges
or reduces the extracted data, and then subjects the data to affine
transformation to erect the trapezoidal region. Further, it
performs data conversion on each coordinate value of the map data
by using the perspective projection processing (step 3). At this
time, the coordinate transformation based on the affine
transformation is represented by the following equation (1): where
.phi. represents the rotational angle of the map, (x, y) represents
the coordinate value Of the map data before the affine
transformation, and (x', y') represents the coordinate value of the
map data before the affine transformation, 1 ( x ' y ' ) = ( cos -
sin sin cos ) ( x y ) ( 1 )
[0090] The coordinate transformation in the perspective projection
processing is represented by the following equations (2) and (3):
where (Tx,Ty,Tz) represents the position coordinate of the view
point, .theta. represents the intersection angle between the planes
A and B, (x,y) represents the coordinate value of the map data
before the transformation, and (x',y') represents the coordinate
value of the map data after the transformation,
x'=(Tx+x)/(Tz+y.multidot.sin .theta.) (2)
y'=(Ty+y.multidot.cos .theta.)/(Tz+y.multidot.sin .theta.) (3)
[0091] In step 3, a drawing target region which is the trapezoid 72
in the step 2 is converted to the rectangular region 74, and the
circumscribed rectangle 73 of the trapezoid 72 is
coordinate-transformed to a rectangle 75 which is circumscribed
around the rectangle 73. It is not necessary to draw regions other
than the drawing target region 74 in the rectangle 75. Therefore,
the coordinate transforming means 62 uses the data clip means 64 to
perform the clip processing on the regions other than the rectangle
region 74 which is the drawing target, thereby removing these
regions (step 4).
[0092] The map data thus obtained are transmitted to the drawing
command issuing means 65. The drawing command issuing means 65
generates a drawing command on the basis of the transmitted map
data and supplies the drawing command to the graphics processing
unit 49 to prepare drawing data. The graphics processing means 49
prepares the drawing data and stores the data into the VRAM 26, and
instructs the display 2 to display the data. The display 2 displays
the drawing data held in the VRAM 26 on the screen thereof. With
the above operation, the bird's-eye view 102 shown in FIG. 1 is
displayed on the screen of the display 2.
[0093] The bird's-eye view display facilitates recognition of the
directional and positional relationship between any two points. In
addition, the bird's-eye view display suitable for use in a case
where detailed information on the periphery of a point is required
to be provided whereas rough information on the peripheries of the
other points is sufficient. As described above, when detailed
information or rough information on the periphery of a specific
point is supplied, the coordinate of the specific point may be
predetermined. Alternatively, the position may be set by
determining a coordinate which satisfies a predetermined condition,
or the position of the point may be input externally.
[0094] According to the navigation system, in many cases the
current position is set to one of the above two points. The
position information of the current position is obtained by the
current position calculating means 45 or the map match processing
means 46. Therefore, when the current position is indicated to any
one of a detailed information display position and a rough
information display position through the input device 5, the map
drawing means 44 uses the coordinate of the current position which
is obtained by the current position calculating means 45 or the map
match processing means 46.
[0095] However, when an instruction of a position on the map
displayed on the screen is received and the instructed position is
set as either the detailed information display position and the
rough information display position, in many cases the user performs
a scroll display on the map to search for the position for which
the detailed information or rough information is displayed.
However, the scroll-speed in the bird's-eye view display is low
because the overall drawing operation must be repeated again every
time a region to be displayed is changed. Accordingly, when the
scroll display is used very frequently, the bird's-eye view display
mode is inconvenient.
[0096] In order to solve this problem, this embodiment adopts the
processing shown in FIG. 8 in the coordinate transformation.
[0097] First, the coordinate transforming means 62 performs an
enlarging or reducing operation for a region to be processed (step
1010) if the map is required to be enlarged or reduced (step 1000),
and also performs a rotational transformation processing (step
1030) if the map is required to be rotated (step 1020). The
rotational transformation processing (step 1030) contains a
rotational angle calculating operation (step 1031) and an affine
transforming operation (step 1032).
[0098] Subsequently, the coordinate transforming means 62 judges
whether the bird's-eye view display is performed (step 1040). Here,
for example when an instruction to search for any point from the
map is input through the input device 5, or when an instruction for
display of the plan-view map is input through the input device 5,
the coordinate transforming means 62 judges that the perspective
projection (conversion) is not performed in the bird's-eye display
judgement (step 1040), and finishes the coordinate transformation
processing without performing the perspective projection processing
(step 1050). In this case, the plan view map is displayed on the
screen of the display 2 because the perspective projection
processing is not performed.
[0099] According to this embodiment, when any point on the map is
searched for, the map is not displayed in the bird's-eye view
display mode, but displayed in the plan-view display mode, so that
the search target point can be rapidly searched for.
[0100] Further, for example when an instruction for displaying the
bird's-eye view is input through the input device 5, or when any
point is instructed as a destination through the input device 5
during the plan-view display, the coordinate transforming means 62
which receives these instructions through the user's operation
analyzing means 41 judges, in the bird's-eye view display judgment
in step 1040, that the perspective projection processing should be
performed, and thus it performs the perspective projection
processing (step 1050).
[0101] The perspective projection processing (step 1050) contains a
projection angle calculation processing (step 1051), a
projection-plane position calculation processing (step 1052) and a
perspective projection operation (step 1053). With this processing,
the map data which are notified to the drawing command issuing
means 65 are converted to data for the bird's-eye view, and thus
the map data which are prepared by the graphics processing means 49
and stored in the VRAM 26 also become data for the bird's-eye view.
Accordingly, the map displayed on the display 2 is changed from the
plan-view map to the bird's-eye view map.
[0102] As described above, the map can be freely changed from the
bird's-eye view map to the plan-view map or from the plan-view map
to the bird's-eye view map. Therefore, according to this
embodiment, an easily-understandable map display can be
provided.
[0103] Further, when the display frame is switched from the
plan-view frame to the bird's-eye view frame in the above
processing, or when the switching of the plan-view map to the
bird's-eye view map or from the bird's-eye view map to the
plan-view map is instructed through the input device 5 or the like,
it would be difficult for the user to recognize the map if the
switching operation between the plan-view map and the bird's-eye
view map is rapidly performed, because the display style of the map
varies greatly on the screen. Therefore, it is preferable that the
shift between the plan-view map and the bird's-eye view map is
performed gradually.
[0104] In this embodiment, when the display frame switching
operation from the plan-view map to the bird's-eye view map is
required, the projection angle 0 is gradually increased from
0.degree. with a time lapse (every 0.5 seconds in this embodiment)
during the projection angle .theta. calculation (step 1051) in the
perspective projection processing (step 1050), and this increase of
the projection angle is stopped until the projection angle reaches
a target projection angle. In this case, the increment unit of the
projection angle is preferably set to a constant value.
[0105] As described above, the plan-view display is smoothly
shifted to the bird's-eye view display by performing the
perspective projection processing (step 1053) while increasing the
projection angle with variation of time, so that the user can
easily grasp the positional relationship between the places (spots)
in the plan-view map and the bird's-eye view map. When the
switching operation from the bird's-eye view display to the
plan-view display is performed, the same effect can be obtained by
gradually reducing the projection angle from an initially-set
projection angle to 0.degree. in time series.
[0106] Next, a method of determining the intersection angle .theta.
(projection angle) between the map and the projection plane which
is a perspective projection parameter in the bird's-eye view
display, and the coordinate of the origin (Tx, Ty, Tz) of a view
point coordinate system containing the projection plane, which is
viewed from an object coordinate system containing the plane of the
map, that is, the position of the projection plane, will be
described with reference to FIGS. 8 and 9A-9C.
[0107] It is generally desired for the navigation system to display
a place at which the user's vehicle runs, that is, the periphery of
the current position of the vehicle, in more detail. Therefore, the
case where the bird's-eye view is displayed such that the current
position is located at the central lower side of the screen as
shown in FIG. 9C will first be described. In this case, the front
side of the current position of the vehicle in a vehicle travel
direction and a road map along which the vehicle has travelled
until now is displayed in the bird's-eye view display mode.
Reference numeral 92 in FIG. 9A represents a-visual field
(corresponding to a range to be drawn and displayed in the
bird's-eye view display mode) in a map mesh 91, and the visual
position and the projection angle to obtain a bird's-eye view are
shown in FIG. 9B. In FIG. 9C, the current position and the vehicle
travel direction in the bird's-eye view display are shown. Arrows
as indicated by dotted lines in FIGS. 9A and 9C represent the
vehicle travel direction.
[0108] In order to achieve the bird's-eye view display as shown in
FIG. 9C, the coordinate transforming means 62 first performs a
desired enlargement/reduction processing (step 1000 and 1010), and
then judges that the rotation is needed (step 1020) to determine an
intersection angle .phi. between the vector of the travel direction
and the bottom side of the map mesh as shown in FIG. 9A (step
1031). Further, the coordinate transforming means 62 performs the
affine transformation on the map data to rotate the data by an
angle .phi. (step 1032).
[0109] Since whether or not the bird's-eye view display is to be
performed is judged in step 1040, the coordinate transforming means
62 performs the processing of determining the projection angle and
the visual position (steps 1051 and 1052).
[0110] If the projection angle .theta. is set to a value close to
0.degree., the difference in scale between the near-distance point
and the far-distance point of the view point is reduced. On the
other hand, if the projection angle .theta. is set to a value close
to 90.degree., the difference in scale between the near-distance
point and the far-distance point is increased. In this embodiment,
the projection angle .theta. is normally set to about 30.degree. to
45.degree..
[0111] In this embodiment, the coordinate transforming means 62
changes the projection angle .theta. in accordance with an angle
changing direction instruction (input through the projection angle
changing key 68) which is input from the user's operation analyzing
means 41. That is, upon detection of the angle-increasing
instruction key 68a being pushed down, the user's operation
analyzing means 41 instructs the increase of the projection angle
to the coordinate transforming means 62. Further, every time the
user's operation analyzing means 41 detects that the
angle-increasing instruction key 68a has been pushed down for 0.5
seconds from the projection angle increasing instruction, as
described above, it instructs the increase of the projection angle
to the coordinate transforming means 62. In response to the
projection angle increasing instruction, the coordinate
transforming means 62 increases the projection angle .theta. by
5.degree. (that is, the projection angle rises up by 5.degree.).
The same action is made for the projection angle reducing
instruction. That is, for every 0.5 seconds that the angle-reducing
instruction key 68b continues to be pushed down, the user's
operation analyzing means 41 instructs the reduction of the
projection angle to the coordinate transforming means 62, and in
response to this instruction the coordinate transforming means 62
reduces the projection angle .theta. by 5.degree. (that is, the
projection angle falls by 5.degree.).
[0112] With this above operation, the user can freely set a map
region to be displayed in the bird's-eye view display mode.
Accordingly, when the increase of the projection angle is
instructed, those regions which are farther away from the current
position are displayed on the map because the projection angle
.theta. increases. On the other hand, when the reduction of the
projection angle is instructed, those regions which are in the
neighborhood of the current position are displayed on the map
because the projection angle .theta. decreases.
[0113] Subsequently, the coordinate transforming means 62
determines the position of the projection plane (Tx, Ty, Tz) so
that a differential value (.DELTA.x, .DELTA.y, .DELTA.z) obtained
by subtracting the position of the projection plane (Tx, Ty, Tz)
from the current position (x, y, z) is equal to a fixed value at
all times (step 1052). Further, the coordinate transforming means
62 sets, as an absolute quantity, .DELTA.x to zero and .DELTA.z to
a small value (when it is displayed in a small reduced scale to
meet the scale of the map) or a large value (when it is displayed
in a large reduced scale). Normally, .DELTA.z may be selected so
that the scale of the plan-view display is coincident with the
scale of a point around the center of the bird's-eye view
display.
[0114] The scale of the map is preferably changeable in accordance
with a user's demand. In this embodiment, the coordinate
transforming means 62 changes the scale of the map to be displayed
in accordance with a scale changing instruction from the user's
operation analyzing means 41 (which is input by the scale changing
key 67). That is, when detecting that the enlargement instruction
key 67a has been pushed, the user's operation analyzing means 41
outputs the enlargement instruction to the coordinate transforming
means 62. Further, it instructs the enlargement to the coordinate
transforming means 62 every 0.5 seconds it is detected that the
enlargement instruction key 67a continues to be pushed down from
the instruction of the enlargement. In response to the enlargement
instruction, the coordinate transforming means 62 increases
.DELTA.z by a predetermined value in step 1052. The same action is
made for the reduction instruction. The user's operation analyzing
means 41 instructs the scale reduction to the coordinate
transforming means 62 every 0.5 seconds when the reduction
instruction key 67b and the reduction instruction key 67b continue
to be pushed down, and in response to this instruction the
coordinate transforming means 62 reduces .DELTA.z by a
predetermined value.
[0115] In this embodiment, .DELTA.y may be set to a negative value
as shown in FIGS. 9A to 9C, however, it may be set to a positive
value as shown in FIGS. 15A to 15C. Further, according to this
embodiment, the bird's-eye view can be displayed with no problem
both when the view point position is at the front side of the
current position and when it is at the rear side of the current
position. FIGS. 15A to 15C are diagrams for obtaining a bird's-eye
view of the same range as shown in FIGS. 9A to 9C, in which the
view point is set to a different position. In FIG. 15A, reference
numeral 152 represents a visual field (a range to be drawn and
displayed) in a map mesh 151, and the visual position and the
projection angle for obtaining a bird's-eye view are shown in FIG.
15B. Further, the current position and the vehicle travel direction
in the obtained bird's-eye view are shown in FIG. 15C. Arrows as
indicated by dotted lines in FIGS. 15A and 15C represent the
vehicle travel direction.
[0116] In this embodiment, the coordinate transforming means 62
determines the position of the view point (specifically, .DELTA.y)
in accordance with the view point position (input by the touch
sensor 70) instructed by the user's operation analyzing means 41.
That is, upon detection of the touch sensor 70 being touched, the
user's operation analyzing means 41 indicates the touch position to
the coordinate transforming means 62. In response to this
indication of the position information, the coordinate transforming
means 62 sets .DELTA.y to such a value that the view point is
coincident with the indicated position.
[0117] As described above, according to this embodiment, .DELTA.y
can be set to any value within a broad range containing positive
and negative values in accordance with the user's instruction.
Accordingly, the position to be displayed in detail can be set more
flexibly.
[0118] Finally, the coordinate transforming means 62 performs the
perspective projection processing on each coordinate value of the
map data by using the projection angle .theta. and the position of
the projection plane (Tx, Ty, Tz) thus obtained (step 1053).
Thereafter, the graphics processing means 49 performs the drawing
processing with the obtained map data, whereby the map display is
performed on the screen such that the travel direction is set to
the up-direction at all times and the current position is displayed
at the same point on the screen in the bird's-eye view display
mode, as shown in FIG. 9C and FIG. 15C.
[0119] As described above, in the navigation system, it is
generally desired that the point at which the user travels at
present, that is, the periphery of the current position, is
displayed in more detail. Therefore, in the navigation system of
this embodiment, the current position is displayed at the central
lower side of the screen as shown in FIGS. 9C, 10C, 15C and
16C.
[0120] According to the navigation system of this embodiment,
indication of a destination can be accepted through touching of to
the touch panel 70. Further, when the destination is indicated, the
destination is drawn so as to be contained in the visual field
(range to be drawn on the display frame). At this time, the
coordinate transforming means 62 determines the rotational angle
.phi. so that the current position is located at the central lower
side, and the destination is located at the center upper side (in
FIGS. 10C and 16C).
[0121] A bird's-eye view display method in the above case will be
described with reference to FIG. 8, FIGS. 10A to 10C and FIGS. 16A
to 16C. FIGS. 10A to 10C are diagrams showing a case of obtaining a
bird's-eye view display in which both the current position and the
destination are drawn on the same frame (field of view), and FIGS.
16A to 16C are diagrams showing a case of obtaining a bird's-eye
view display of the same range as show in FIGS. 10A to 10C, in
which the view point is set to a different position. A field of
view (range to be drawn and displayed) 162 is shown in a map mesh
161 in FIGS. 10A and 16A, the view point position and the
projection angle for obtaining the bird's-eye view are shown in
FIGS. 10B and 16B, and the current position and the position of the
destination in the obtained bird's-eye view display are shown in
FIG. 10C and 16 C. Arrows indicated by dotted lines represent the
direction from the current position to the destination.
[0122] In the following description, the current position is
displayed at the central lower side of the screen, and the
destination is displayed at the central upper side of the screen.
The same processing is performed in a case where the display
positions of any two points are selectively set to the central
lower and upper sides of the screen in accordance with an
instruction of the display positions of the two points.
[0123] In order to achieve the bird's-eye view displays shown in
FIG. 10C and 16C, the coordinate transforming means 62 calculates
an intersection angle .phi. between the bottom side of the map mesh
and a line perpendicular to a line connecting the current position
and the destination a shown in FIGS. 10A and 16A in step 1031, and
performs the affine transformation on each coordinate value of the
map data to be drawn by the angle .phi. in step 1032.
[0124] Since it is judged in step 1040 that the bird's-eye view
display is performed, the coordinate transforming means 62 shifts
to the processing for determining the projection angle .theta. and
the view point position (step 1051 and step 1052). As described
above, the initial value of the projection angle .theta. is a
predetermined value in the range of 30.degree. to 40.degree., and
it is changed in accordance with an input operation of the
projection angle changing key 68. Further, as described above, the
initial position of the projection plane is determined so that the
differential value obtained by subtracting the position coordinate
of the projection plane from the coordinate of the current position
is equal to a predetermined value, and it is changed in accordance
with an input operation of the reduction-scale instructing key 67.
Further, the rotation of the coordinates is performed by using the
transforming equations (2) and (3), and the affine transformation
is performed by using the transforming equation (1). Further, the
parameters Ty and Tz which indicate the position of the projection
plane are calculated by substituting a suitable value, for example,
zero into Tx, substituting the position coordinates and the display
positions of the current point and the destination, and then
solving a linear equation system.
[0125] Next, the coordinate transforming means 62 performs the
perspective projection processing (step 1053). That is, the
coordinate transforming means 62 performs the perspective
projection on each coordinate value of the map data on the basis of
the projection angle .theta. and the position of the projection
plane thus obtained.
[0126] The graphics processing means 49 performs the drawing
processing with the obtained map data, whereby the current position
and the destination can be displayed on the same display frame.
Further, if the above processing is performed every time the
current position varies, the current position and the destination
can be displayed at the same positions on the same display frame,
even when the current position varies with time. Further, if the
judgment of the step 1040 is set to judge the necessity of the
perspective projection processing at all times during the
bird's-eye view display, the display of the screen is changed at
all times in accordance with the time variation. Further, if the
judgment of the step 1040 is set to judge the necessity of the
perspective projection processing only when the current position is
shifted by a predetermined distance or more, only the mark 105
indicating the current position on the same bird's-eye view map is
shifted until the current position is shifted by a predetermined
distance, and the map display is varied to an enlarged map display
as the current position is shifted by the predetermined distance
and approaches the destination.
[0127] If the above processing is performed every time the current
position is varied, and the current position and the position of
the destination to be displayed on the screen are set to fixed
positions, the map display could be gradually enlarged as the
current position approaches the destination.
[0128] Further, if the projection angle .theta. is set to be
reduced to a smaller value as the distance between the current
position and the destination is shorter, the display mode is set to
the bird's-eye view display to facilitate the understanding of the
positional relationship between the current position and the
destination when the current position and the destination are far
away from each other, and set to a display mode near to the
plan-view display when the current position approaches the
destination. Conversely, the projection angle .theta. may be
gradually increased to a larger value as the distance between the
current position and the destination becomes shorter. In this case,
when the current position is far way from the destination, the
display mode is set to the plan-view display so that the overall
positional relationship can be easily understood. As the current
position approaches the destination, the visual-point position is
gradually heightened to enhance the user's sense of distance.
[0129] Next, a method of drawing character data in the bird's-eye
view display will be described. First, the details of the
perspective projection processing (step 1053) of the coordinate
transforming means 62 will be described with reference to FIG.
11.
[0130] The coordinate transforming means 62 judges whether input
map data are plane data (step 1100). If the input data are plane
data, the coordinate transforming means 62 performs the perspective
projection (step 1101) on each node coordinate value of the given
plane data by using the parameters obtained by the projection angle
.theta. calculation (step 1051) and the visual-point position
calculation (step 1052). The perspective projection processing of
the node (step 1101) is repeated until the processing on all input
nodes is completed (step 1102).
[0131] Subsequently, the coordinate transforming means 62 subjects
line data to the same processing as the plane data, to perform the
perspective projection on the coordinate value of each node (steps
1103 to 1105).
[0132] When the processing on the line data is completed, the
coordinate transforming means 62 judges whether the input map data
are character data (step 1106). If the input data are judged to be
character data, the perspective transforming means 62 performs the
perspective projection on the coordinate values of drawing start
points of given character strings by using the projection angle
.theta. and the coordinate value of the visual-point position which
are obtained in the steps 1051 and 1052. In this embodiment, no
perspective projection is performed on a character image. The
perspective projection processing of the node in step 1107 is
repeated until the processing on all the input nodes is completed
(step 1108).
[0133] When the graphics drawing is performed with the perspective
projection result thus obtained, such a bird's-eye view map as the
map 103 shown in FIG. 1 is obtained. According to this embodiment,
since no perspective projection is carried out on the character
image in step 1107 as described above, all the characters are drawn
at the same size so as to be erect on the map as shown by the map
103 of FIG. 1.
[0134] Next, the processing of the drawing judgment means 63 will
be described with reference to FIG. 12. The drawing judgement means
63 serve to judge whether each data item contained in the map data
should be drawn.
[0135] First, the drawing judgment means 63 judges whether the
input map data contain plane data (step 1200). If the plane data
are judged to be contained, the drawing judgment means 63 performs
a predetermined plane data drawing judgment processing (step 1201).
The plane data drawing judgment processing (step 1201) which is
carried out in this case serves to judge an attribute which is
preset for each plane data and select desired plane data, for
example.
[0136] When the processing on the plane data is completed, the
drawing judgment means 63 subsequently judges whether the input map
data contain line data such as roads, line backgrounds, etc. (step
1202). If the line data are judged to be contained, the drawing
judgment means 63 performs a predetermined line data drawing
judgment processing (step 1203). The line data drawing judgment
(step 1203) which is carried out in this case serves to judge an
attribute which is preset for each line data and select desired
line data, for example.
[0137] When the processing on the line data is completed, the
drawing judgment means 63 subsequently judges whether the input map
data contain character data (step 1204). If the character data are
judged to be contained, the drawing judgment means 63 performs
rearrangement processing on the coordinate values of drawing start
points of character strings to rearrange the character strings from
the far-distance side to the near-distance side (step 1205).
[0138] Subsequently, the drawing judgment means 63 compares the
height y of the drawing start point of each of the rearranged
character strings with a predetermined height h on the display
frame (step 1206). In this embodiment, when the height of the
display frame is set to "1", the height h is set to the position
corresponding to "2/3" from the bottom side of the display frame.
That is, the height h is set to a predetermined fixed value. This
is because when the height from the bottom side is set to 2/3 or
more, the angle of depression is extremely small, and the density
of nodes to be drawn is excessively high. However, this reference
value (height h) may be set in accordance with the height of the
view point or the like.
[0139] As a judgment criterion for the drawing of the character
strings the distance from the view point may be used in place of
the height from the bottom side of the display frame. For example,
assuming the distance between the view point and the destination to
be "1", only those character strings which are located at a
distance of "2/3" or less from the view point are drawn, and those
character strings which are located at a distance longer than "2/3"
are eliminated from drawing targets.
[0140] If the height y of a drawing start point of a character
string is judged to be lower than the height h as a position
judgment result, the drawing judgment means 63 sets the character
string as a drawing target. On the other hand, if the height y is
judged to be higher than the height h, the drawing judgment means
63 eliminates the character string from the drawing targets (step
1207). In this embodiment, the graphics processing means 49
performs the drawing operation by using the map data which are
selected by the drawing judgment means 63 as described above, so
that the bird's-eye view display can be prevented from being made
too intricate, and a clear and lucid display can be obtained.
[0141] Further, according to this embodiment, the drawing of a
character string is determined on the basis of only the height of
the display position thereof. In place of this method of
determination, the following method may be used. That is, a display
priority rank (order) is preset for each character string, and a
range of the display ranks of character strings to be displayed is
set in accordance with the display height (or distance from the
view point) of the character strings. In this case, only the
character strings to which the display ranks contained in the range
are allocated are displayed. For example, the upper limit of the
display ranks of the character strings to be displayed is set to a
fixed rank irrespective of the height of the character string, but,
the lower limit of the display ranks of the character strings is
set to a higher rank in accordance with the height of the character
string on the display frame. In this case, in an area close to the
upper side of the display frame, only character strings having
higher display priority ranks are displayed. On the other hand, in
an area close to the bottom side of the display frame, not only
character strings having higher display ranks, but also character
strings having lower display ranks are displayed. Accordingly, when
the current position is set to a position close to the bottom side
of the display frame, more detailed character information can be
obtained for an area as the area becomes closer to the current
position. If the area is farther away from the current position,
only important information is displayed. Accordingly, this display
mode is very convenient for users.
[0142] Further, when an attribute (font of display character,
meaning of character string, or the like) is previously allocated
to each character string, the attribute may be used as another
criterion for the display priority ranking. In this case, only
characters having predetermined attributes may be displayed in each
region.
[0143] If a character string is defined for a predetermined point
serving as a destination, only the character string may be
displayed.
[0144] The steps 1205 to 1207 may be omitted, but, these steps are
preferably executed. The effect of these steps will be described
with reference to FIGS. 13A, 13B, 14A and 14B.
[0145] FIG. 13A shows a bird's-eye view map obtained when the
drawing operation is carried out without performing the
rearrangement processing and the drawing character string selecting
processing of steps 1205 to 1207. FIGS. 13B and 14A shows a
bird's-eye map obtained when the drawing operation is carried out
together with performing the rearrangement processing of step 1205,
but without performing the drawing character string selecting
processing of steps 1206 and 1207. FIGS. 14B shows a bird's-eye
view map obtained according to this embodiment, that is, a
bird's-eye view map obtained when the processing of steps 1205 to
1207 is performed. In FIGS. 13A to 14B, figures, etc. which are
drawn on the basis of plane data and line data are omitted from the
illustration.
[0146] When the bird's-eye view is displayed without performing the
rearrangement processing of step 1205, character strings are
displayed merely in a stored order of the character strings,
irrespective of the distance to the view point, as shown in FIG.
13A. Therefore, a character string which is far away from the view
point (a far-distance character string) may be displayed while
superposed on a character string which is close to the view point
(a near-distance character string).
[0147] On the other hand, in the case where the rearrangement
processing of the character string of step 1205 is performed, if a
far-distance character string is overlapped with a near-distance
character string, the near-distance character string is displayed
while superposed on the far-distance character string. Such a
bird's-eye view display mode as described above is very preferable
because as an area approaches the current position, this display
mode makes it easier to read information for the area.
[0148] Further, in the case where the bird's-eye view is displayed
without performing the drawing character string selecting
processing of steps 1206 and 1207, as a character becomes farther
away from the view point, the angle of depression of the character
string with respect to the view point becomes smaller, so that the
character string is reduced and compressed more and more, as shown
in FIG. 14A. Therefore, the data amount of line, planes and
characters to be drawn per unit area is increased. The character
data of these data are drawn while superposed on the other data, so
that the line and plane background data are hidden by the character
data. Therefore, it is very difficult to read plane information
such as remote roads, rivers, green zones, etc. from the display
frame in the above bird's-eye view display.
[0149] On the other hand, according to this embodiment, in order to
perform the drawing character string selecting processing of steps
1206 and 1207, character data in a range (character drawing range)
extending from the bottom side of the display frame to the height h
are drawn while the other data are not drawn as shown in FIG. 14B.
Accordingly, in a bird's-eye view display obtained according to
this embodiment, the plane information such as roads, rivers, green
zones, etc. which are remote from the view point can be easily read
from the display frame.
[0150] The bird's-eye view display apparatus and the navigation
system according to this embodiment can display a map which is
expressed in a bird's-eye view display mode. Accordingly, the user
can obtain a clear map display in which the positional relationship
can be easily recognized. In addition to this effect, the following
effects are also expected to be obtained by this embodiment.
[0151] First, according to this embodiment, it's easy to switch
between the plan-view display and the bird's-eye view display.
Accordingly, both the plan view and the bird's-eye view can be
displayed in accordance with the user's demand.
[0152] Secondly, according to this embodiment, when the bird's-eye
view display and the plan-view display are switched, the
intersection angle between a plane containing map data and a plane
to which a map is projected is gradually increased or reduced in
time series. That is, in the switching operation between the
plan-view display mode and the bird's-eye view display mode, the
view point to obtain the bird's-eye view is smoothly shifted.
Accordingly, the user can easily recognize the positional
correlation between the spots displayed on the plan-view map and
the spots displayed on the bird's-eye view map because the shift
between the plan-view map and the bird's-eye view map is performed
smoothly.
[0153] Thirdly, according to this embodiment, the view point to
obtain the bird's-eye view can be fixed to a position which is away
from the current position at a fixed distance and in a fixed
direction at all times. Further, the height of the view point can
be varied in accordance with an input operation received
externally. If the view point is fixed, the bird's-eye view is
displayed such that the current position is fixed to a specific
position on the screen at all times, so that the user can easily
grasp the current position. Further, the view point can be set to
any position desired by the user.
[0154] Fourthly, according to this embodiment, when the positions
of two points (for example, a current position and a destination)
are specified, the view point and the intersection angle between
the plane containing the map data and the plane to which the map is
projected are determined so that the two points are displayed at
the specified positions on the screen, and the bird's-eye view
display is performed on the basis of the above determination
result. Accordingly, the user can easily recognize the positional
relationship between the two points. Further, even when the
distance between the two points varies, the two points are
displayed on the same display frame at all times, so that the user
can easily grasp the positional relationship between the two points
with no complicated operation.
[0155] Fifthly, the coordinate transforming means of this
embodiment performs no perspective projection processing on the
character image. Accordingly, all characters contained in the
bird's-eye view are displayed at the same size so as to be erect on
a map, so that the user can easily read these characters.
[0156] Sixthly, the drawing judgment means of this embodiment sorts
character data strings in accordance with the distance of the
character data position to the view point on the map data. That is,
as a character string approaches the view point, the character
string is treated so as to have a higher display priority rank.
Accordingly, the character data close to the view point can be
prevented from being covered and missed by the other character
data, so that character information close to the view point can be
easily identified.
[0157] Seventhly, when a character string obtained through the
perspective projection processing is located at a position higher
than a predetermined height on the screen, the drawing judgment
means of this embodiment eliminates the character string, from
drawing targets. The drawing judgment means may eliminate from the
drawing targets those character strings which are defined at
positions away from the view point at a predetermined distance or
more. As described above, no character string is drawn in an area
which is at a predetermined height or more or away from the view
point at a predetermined distance or more, that is, in an area in
which the data amount to be drawn per unit area is considerably
increased due to reduction of the angle of depression in the
bird's-eye view display. Therefore, the road display, the plane
background display, etc. in this area are not covered by the
character string display, so that the user can recognize
far-distance roads, etc. with no obstruction.
[0158] According to the bird's-eye view display apparatus and the
navigation system of the present invention, the map can be
displayed in the bird's-eye view display mode. Accordingly, the
user can obtain a map display in which the positional relationship
between spots displayed on a map can be easily recognized.
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