U.S. patent application number 08/800331 was filed with the patent office on 2001-11-22 for method and apparatus for displaying road map in form of bird's eye view.
Invention is credited to SONE, GAKU.
Application Number | 20010043212 08/800331 |
Document ID | / |
Family ID | 12519257 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043212 |
Kind Code |
A1 |
SONE, GAKU |
November 22, 2001 |
METHOD AND APPARATUS FOR DISPLAYING ROAD MAP IN FORM OF BIRD'S EYE
VIEW
Abstract
In method and apparatus for displaying a road map mesh in a form
of a bird's eye view on a display screen of a display unit, a
virtual viewpoint at an upper sky behind a predetermined point of
display reference (such as a present position of a mobile body,
e.g., a vehicle) by a predetermined spatial distance is set, a part
of the plan view formed road map mesh Z which is ahead of the
predetermined display reference point is looked down along a line
of sight along a predetermined looking down angle, the display
screen Y is set on a plane vertical to the line of sight, the road
map data on the plan view formed road map mesh corresponding to
respective pixles on the display screen Y are extracted, and the
bird's eye view on the display region X for the bird's eye view on
the plan view formed road map mesh Z on the display screen Y on the
basis of the extracted road map data.
Inventors: |
SONE, GAKU; (TOKYO,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Family ID: |
12519257 |
Appl. No.: |
08/800331 |
Filed: |
February 14, 1997 |
Current U.S.
Class: |
345/427 |
Current CPC
Class: |
G06T 15/20 20130101 |
Class at
Publication: |
345/427 |
International
Class: |
G06T 015/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 1996 |
JP |
8-38221 |
Claims
What is claimed is:
1. A method for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit, comprising: a) storing
the road map mesh in a form of a plan view; b) placing a virtual
viewpoint at an upper sky behind a predetermined position of
display reference on the plan view formed road map mesh by a
predetermined distance; c) looking down at the plan view formed
road map mesh forward away from the predetermined point of display
reference from said virtual viewpoint along a line of sight having
an angle of field of view with respect to the predetermined point
of display reference; d) setting the display screen on a plane
perpendicular to the line of sight; e) extracting road map data
from the plane view formed road map mesh corresponding to
respective pixels on the display screen from the plan view formed
road map mesh; and, f) drawing the bird's eye view of the plan view
formed road map mesh on the display screen on the basis of the
extracted road map data.
2. A method for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit as claimed in claim 1,
which further comprises the step of dividing the display screen
into a plurality of display regions and wherein the road map data
are extracted from the road map mesh for the respective display
regions and, at the step e), the bird's eye view is drawn on the
divided display regions of the display screen on the basis of the
road map data for each display region.
3. A method for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit as claimed in claim 2,
wherein said predetermined point of display reference is a present
position of a mobile body which carries an apparatus for displaying
a road map mesh in the form of the bird's eye view on the display
screen of the display unit.
4. A method for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit as claimed in claim 3,
wherein said mobile body is an automotive vehicle.
5. A method for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit as claimed in claim 4,
wherein the road map data on the plan view formed road map mesh
having a scale of reduction A comprise a plurality of dots with set
colors and wherein, at the step d), the dots other than those
corresponding to the respective dots on the display screen are
omitted from those on the plan view formed road map mesh having the
scale of reduction so as to achieve the bird's eye view of the plan
view formed road map mesh on the display screen X.
6. A method for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit as claimed in claim 5,
wherein said steps e) and f) comprise the steps of: g) setting a
bird's eye view display region (X) on the plan view formed road map
mesh (Z) according to a bird's eye view display condition including
a height of said virtual viewpoint from the plan view formed road
map mesh, the angle of field of view, and a distance from the
viewpoint to the display screen; h) setting matrix coordinates (m,
n) within the bird's eye view display region (X) according to the
bird's eye view display condition; and i) extracting only the dots
on the set matrix coordinates at the step h) so as to display the
bird's eye view of the plan view formed road map mesh.
7. A method for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit as claimed in claim 6,
wherein said scale of reduction A of the plan view formed road map
mesh is expressed as follows: A={{square root}{square root over (
)}(a.sup.2+d.sup.2).times- .sin (.theta.+tan.sup.-1(a/d))}/h,
wherein a denotes a half of the height of the display screen
itself, d denotes a straight distance from the viewpoint to the
display screen, .theta. denotes the angle of field of view from the
viewpoint to the predetermined point of display reference, and h
denotes a height of the virtual viewpoint from the plan view formed
road map mesh having the scale of reduction A.
8. A method for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit as claimed in claim 7,
wherein, if h' denotes a height of the viewpoint from the plan view
formed road map mesh having the scale reduction of 1/1 with the
distance from the viewpoint to the display screen d, the angle of
the field of view from the viewpoint to the predetermined point of
display reference .theta., and the height 2a of the display screen
itself being set constants, a display region in which the bird's
eye view is displayed in the case of the height h has the same as
that in the case of the height h'.
9. An apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit, comprising: a
memory arranged for storing the road map mesh in a form of a plan
view; and a picture drawing processor arranged for placing a
virtual viewpoint at an upper sky behind a predetermined point of
display reference by a predetermined distance, looking down at the
plan view formed road map mesh forward away from the predetermined
point of display reference from said virtual viewpoint along a line
of sight having an angle of field of view with respect to the
predetermined point of display reference, setting the display
screen on a plane perpendicular to the line of sight, extracting
road map data on the plan view formed map mesh corresponding to
respective pixies on the display screen from the plan view formed
road map mesh, and drawing the bird's eye view of the plan view
formed road map mesh on the display screen on the basis of the
extracted road map data.
10. An apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit as claimed in claim
9, which further comprises a command input operation unit arranged
for inputting a scroll command to said picture drawing processor
extracts the road map data on the plan view formed road map mesh
corresponding to respective pixels on the display screen from the
plan view formed road map mesh and draws the bird's eye view of the
plan view formed road map mesh on the display screen on the basis
of the extended road map data while said scroll command is received
thereby.
11. An apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit as claimed in claim
10, wherein said picture drawing processor further executes a
perspective transformation of the plan view formed road map into
the bird's eye view so as to display the transformed bird's eye
view on the display screen when the scroll command input to the
picture drawing processor is ended.
12. An apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit as claimed in claim
11, wherein said picture drawing processor divides the display
screen into a plurality of display regions and wherein said picture
drawing processor extracts the road map data from the road map mesh
for the respective display regions and the bird's eye view is drawn
on the divided display regions of the display screen on the basis
of the road map data for each display region.
13. An apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit as claimed in claim
12, wherein said memory stores character data on the road map mesh
and wherein said picture drawing processor executes the extraction
of the road map data without extracting of the character data on
the road map mesh.
14. An apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit as claimed in claim
13, which further comprises a Video-RAM capable of temporarily
storing a predetermined region (L) of the road map data on the plan
view formed road map mesh, wherein said picture drawing processor
determines whether the display region (X) of the bird's eye view
overflows the predetermined region (L), and wherein said picture
drawing processor updates the road map data on the plan view formed
road map mesh when determining that the display region (X) of the
bird's eye view overflows the predetermined region (L).
15. An apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit as claimed in claim
14, wherein said road map data includes road lines and
polygons.
16. An apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit as claimed in claim
12, wherein a scale of reduction of each display region is varied
according to a distance of the corresponding one of the regions to
be displayed from the predetermined point of display reference.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to method and apparatus for
displaying a road map in a form of bird's eye view.
[0002] The present invention is applicable to apparatus for
navigating a vehicle to a destination using a display unit.
[0003] A Japanese Patent Application First Publication No. Heisei
7-190791 exemplifies a previously proposed apparatus for executing
a coordinate transformation of a plan view formed road map piece
(mesh) into a bird's eye view (perspectively projected view).
[0004] However, since the previously proposed apparatus executes
the coordinate transformation even if a scrolling operation for a
display screen is carried out, a processor capable of processing a
large amount of data (a processor having a high processing
capability) is required in order to maintain a scrolling velocity
to some degree. This causes an increase in a total cost of
assembling the whose apparatus.
SUMMARY OF THE INVENTION
[0005] It is an object of the present invention to provide method
and apparatus for displaying a road map mesh in a form of bird's
eye view on a display screen of a display unit without use of a
processor having a high processing capability and at a high drawing
velocity of the bird's eye view.
[0006] The above-described object can be achieved by providing a
method for displaying a road map mesh in a form of bird's eye view
on a display screen of a display unit, comprising:
[0007] a) storing the road map mesh in a form of a plan view;
[0008] b) placing a virtual viewpoint at an upper sky behind a
predetermined position of display reference on the plan view formed
road map mesh by a predetermined distance;
[0009] c) looking down at the plan view formed road map mesh
forward away from the predetermined point of display reference from
said virtual viewpoint along a line of sight having an angle of
field of view with respect to the predetermined point of display
reference;
[0010] d) setting the display screen on a plane perpendicular to
the line of sight;
[0011] e) extracting road map data from the plane view formed road
map mesh corresponding to respective pixels on the display screen
from the plan view formed road map mesh; and,
[0012] f) drawing the bird's eye view of the plan view formed road
map mesh on the display screen on the basis of the extracted road
map data.
[0013] The above-described object can also be achieved by providing
an apparatus for displaying a road map mesh in a form of bird's eye
view on a display screen of a display unit, comprising:
[0014] a memory arranged for storing the road map mesh in a form of
a plan view; and
[0015] a picture drawing processor arranged for placing a virtual
viewpoint at an upper sky behind a predetermined point of display
reference by a predetermined distance, looking down at the plan
view formed road map mesh forward away from the predetermined point
of display reference from said virtual viewpoint along a line of
sight having an angle of field of view with respect to the
predetermined point of display reference, setting the display
screen on a plane perpendicular to the line of sight, extracting
road map data on the plan view formed map mesh corresponding to
respective pixles on the display screen from the plan view formed
road map mesh, and drawing the bird's eye view of the plan view
formed road map mesh on the display screen on the basis of the
extracted road map data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an explanatory view for explaining a relationship
between a (virtual) viewpoint, a display screen for a bird's eye
view, and a region of the bird's eye view on a plan view formed
road map mesh.
[0017] FIG. 2 is a relationship between a height of the viewpoint
from the plan view formed road map mesh and a scale of reduction
that the plan view formed road map mesh has.
[0018] FIG. 3 is an explanatory view for explaining the
relationship between the plan view formed road map mesh Z having
the scale of reduction A and shown in FIG. 2, the display region X
for the bird's eye view on the plan view formed road map mesh Z,
and the display screen Y.
[0019] FIG. 4 is an explanatory view for explaining a pattern of
adopted data (dots, black quadrangles) and unadopted data (dots,
blank (white) quadrangles) not to be displayed as the bird's eye
view on the plan view formed road map (Z) having the scale of
reduction A.
[0020] FIG. 5 is an explanatory view of an arrangement of a dot
pattern on the plan view formed road map mesh.
[0021] FIG. 6 is a circuit block diagram of an apparatus for
displaying a road map mesh in a form of bird's eye view on a
display screen of a display unit in a preferred embodiment
according to the present invention.
[0022] FIG. 7 is an operational flowchart executed in the road map
mesh displaying apparatus shown in FIG. 6.
[0023] FIG. 8 is an explanatory view representing a relationship
between a region X capable of drawing the road map mesh on a V-RAM
shown in FIG. 6 and a region X capable of displaying the bird's eye
view .
[0024] FIG. 9 is an explanatory view of explaining a procedure to
transfer an information of the dots adopted to represent the bird's
eye view to a buffer.
[0025] FIG. 10 is an explanatory view of the information on the
dots adopted to represent the bird's eye view stored in the
buffer.
[0026] FIGS. 11(A) and 11(B) are explanatory view for explaining a
method of transmitting a video signal from the buffer to the
display unit shown in FIG. 6.
[0027] FIG. 12 is an explanatory view for explaining a modification
of the preferred embodiment in which the display screen is divided
into a plurality of display regions.
[0028] FIG. 13 is an explanatory view for explaining a dot pattern
on each divided display region in the case of the modification of
the preferred embodiment shown in FIG. 12.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] Reference will hereinafter be made to the drawings in order
to facilitate a better understanding of the present invention.
[0030] FIG. 1 shows a relationship between a (virtual) viewpoint of
a bird's eye view, a display screen on the bird's eye view, and a
display region for the bird's eye view to be displayed on a plan
view formed road map mesh.
[0031] It is noted that the road map mesh is a square shaped road
map of topographical road map, i.e., a predetermined piece of
regional (local) road map. One road map mesh is divided into the
road map mesh pieces to be described later.
[0032] A road map in a form of the bird's eye view is prepared
(generated) as follows:
[0033] First, the virtual viewpoint is set at an upper sky position
whose height is predetermined behind a predetermined point of
display reference (in the case of a navigation system, the
predetermined display reference point corresponds to a present
position of a vehicle in which the navigation system is mounted).
And, a forwarding direction (an opposite direction to the viewpoint
with the display reference point included) is looked down along a
line of sight through a predetermined looking down angle (an angle
of field of view) and a display screen for the bird's eye view is
set on a plane perpendiculalr (vertical) to the line of sight.
Then, a perspective projection transformation of the plan view
formed road map mesh from the viewpoint through the display screen
for the bird's eye view is carried out. That is to say, a
coordinate transformation of the plan view formed road map mesh
data represented by plan view road map coordinates into the display
screen coordinates on the bird's eye view.
[0034] It is herein noted that if the height of viewpoint from the
plan view formed road map mesh is varied from among the height of
the viewpoint, the looking down angle, and a distance from the
viewpoint to the display screen, the displayed region is
accordingly varied. However, if, at the same time when the height
of the viewpoint is varied, a scale of reduction of the plan view
formed road map mesh, the same region can be displayed.
[0035] FIG. 2 shows a relationship between the height of the
viewpoint and the scale of reduction of the plan view formed road
map mesh (piece).
[0036] As shown in FIG. 2, it is possible to display the same
region on the plan view formed road map mesh, if the scale of
reduction of the plan view formed road map mesh is made smaller
(1/1, 1/2, . . . , 1/n) at the same time when the height of the
viewpoint is lowered.
[0037] Suppose now that the height of the viewpoint from the plan
view formed road map mesh having the scale of reduction A is h, the
looking down angle is .theta., the distance between the viewpoint
and display screen is d, and the height (width in a vertical
direction) of the display screen is 2a.
[0038] When the height h of the viewpoint is lowest, the scale of
reduction A of the plan view formed road map mesh is expressed as
follows:
A={{square root}{square root over ( )}a.sup.2+d.sup.2).times.sin
(.theta.+tan.sup.-1(a/d))}/h . . . (1).
[0039] Suppose that a height of the viewpoint from the plan view
formed road map mesh having the scale of reduction of 1/1 is
denoted by h'.
[0040] If the angle of the field of view (looking down angle)
.theta., the distance from the viewpoint to the display screen d,
and the display screen height 2a are set to constants, the display
region when the plan view formed road map mesh having the scale of
reduction A is displayed in the form of the bird's eye view is the
same as that when the plan view formed road map mesh having the
scale of reduction of 1/1.
[0041] Next, a new method will be described which displays the plan
view formed road map mesh having the scale of reduction A on the
display screen having the height 2a under a display condition
including the height h of the viewpoint, the looking down angle
.theta., and the distance d between the viewpoint and the display
screen.
[0042] This new method according to the present invention is
carried out without the above-described coordinate transformation
from the plan view formed road map mesh to the bird's eye view
display screen.
[0043] FIG. 3 shows a relationship between the plan view formed
road map (mesh) Z having the scale of reduction A in FIG. 2, the
display region X in which the bird's eye view is displayed on the
plan view formed road map (mesh) Z, and the display screen Y of the
bird's eye view.
[0044] The display unit to display the road map sets a display
color for each dot to form one display screen. The display screen
of the display unit is constituted by a predetermined number of the
dots. One dot means a minimum unit of display, i.e., a pixel.
[0045] During the coordinate transformation from the plan view
formed road map Z having the scale of reduction A to the display
screen Y, the x axis and y axis of both plan view formed road map
mesh Z and display screen Y are handled at the same scale so that
the plan view formed road map mesh Z having the scale of reduction
A may be considered to be constituted by the same dots of
coarseness as the display screen Y.
[0046] In the plan view formed road map mesh Z having the scale of
reduction A and the display screen Y having the mutual relationship
to each other, a straight line is virtually drawn from the
viewpoint to the plan view formed map mesh Z passing through a
center of each dot on the display screen Y so that the dot at a
point of each straight line intersected with the plan view formed
road map mesh Z corresponds to the dot corresponding to each dot
having the display screen Y is defined as a dot corresponding to
each dot on the display screen Y.
[0047] The display color set on the corresponding one of the dots
on the plan view formed road map mesh is a display color of each
corresponding dot on the display screen Y to form one screen.
Consequently, the bird's eye view in the display region X can be
represented on the display screen Y without execution of the
coordinate transformation described above.
[0048] In other words, if the dots other than those corresponding
to the respective dots of the display screen Y are omitted
(unadopted) from the dots present on the plan view formed road map
mesh Z having the scale of reduction A, the display region X of the
plan view formed road map mesh Z can be displayed in the form of
the bird's eye view.
[0049] FIG. 4 shows a dot pattern of the adopted dots (black
quadrangles) for the bird's eye representation and the omitted
(unadopted) dots (blank quadrangles) not for the bird's eye
representation on the plan view formed road map mesh Z having the
scale of reduction A shown in FIG. 3.
[0050] These adopted dots on the plan view formed road map mesh Z
are dots corresponding to the respective dots on the display screen
Y shown in FIG. 3. This dot pattern is varied according to the
display condition such as the height of the viewpoint, the looking
down angle, and the distance between the viewpoint and the displace
screen. Hence, it is desirable for the dot patterns which
correspond to the various display conditions of the bird's eye view
to be stored previously in a memory.
[0051] Or, alternatively, since the display condition on the bird's
eye view is not frequently varied, the dot pattern may be
calculated at a time when the above-described display condition is
established.
[0052] In a preferred embodiment of a method for displaying the
road map mesh in the form of the bird's eye view, each dot on the
plan view formed road map mesh Z is represented by a matrix
coordinate of a line (n=1, 2, 3, . . . ) and a column (m=1, 2, 3, .
. . ), as a minimum square shape including the bird's eye view
region X. It is noted that Z denotes a region enclosing the display
region X of the bird's eye view on the plan view formed road map
mesh having the scale of reduction A.
[0053] FIG. 6 shows a structure of the apparatus for displaying the
road map mesh in the form of the bird's eye view in the preferred
embodiment according to the present invention.
[0054] A main processor processor 1 executes a sequence control of
the whole apparatus and various types of calculations. An operation
board 3 is connected to the main processor 1 via an interface
2.
[0055] The operation board 3 includes a direction key(s) to scroll
the display screen. A ROM (Read Only Memory) 4 stores various
processing programme such as for the scrolling operation.
[0056] A picture drawing (purpose) processor 5 carries out the
bird's eye view drawing processing by means of the adopted and
unadopted dots (dot extracting process), (the bird's eye view
drawing processing caused by the coordinate transformation), and
the scrolling process. A color palette 6, a video signal interface
7, a display 8, ROM (character generator) 9, a video-RAM (V-RAM) 10
are connected to the picture drawing processor 5. The RAM 11 is
used for the temporary storage of the various data.
[0057] The picture drawing processor 5 is connected with an
external CD-ROM 14 for storing plan view formed road mesh(es) via a
decoder 12 and a driver 13.
[0058] FIG. 7 shows an operational flowchart indicating the
scrolling process.
[0059] In the embodiment, the picture drawing processor 5 starts
the processing routine of FIG. 7 when the scrolling process is
carried out via the operation board 3.
[0060] At a step S1, the CPU (the picture drawing processor) 5
reads the plan view formed road map mesh data from the CD-ROM 14
and draws the plan view formed road map mesh having the
predetermined scale of reduction A. It is noted that, at this time,
the information which becomes unclear when the bird's eye view is
displayed due to the omission of the dots, namely, the characters
or symbols are not drawn but the information of line represented
roads and railways and a polygon information such as a park or lake
are drawn.
[0061] At the subsequent step S2, the picture drawing processor 5
determines the display region X for the bird's eye view on the
basis of the display condition on the bird's eye view such as the
previously set height of the viewpoint h, the looking down angle
.theta., and the distance between the viewpoint and display
screen.
[0062] FIG. 8 shows the relationship between the road map mesh
drawing range K on the V-RAM 10 and the display region X of the
bird's eye view.
[0063] The V-RAM 10 has a sufficient capacity to a degree such that
even when the display region X for the bird's eye view is moved
within the plan view formed drawing range K in response to the
scrolling process of the display screen, the display region X does
not immediately fall out of (overflow) the drawing range K
(predetermined region K). The region Z is a region in the minimum
square shape including the display region X of the bird's eye
view.
[0064] The region L is a region to determine the update of the plan
view formed road map mesh on the V-RAM 10.
[0065] Referring back to FIG. 7, at a step S3, the picture drawing
processor 5 transfers the information of the adopted dots (values
of Red, Green, and Blue (R, G, B) only along the line in which the
adopted dots (at least one adopted dot) for the bird's eye view are
present from a line 0 of the region Z in a sequence of younger
column number into a buffer of the picture drawing processor 5.
[0066] For example, in a case where the adopted dots are present in
the line n and in the (n+4) line as shown in FIG. 9, the
information on the adopted dots is stored in the buffer as shown in
FIG. 10.
[0067] Next, at a step S4, the information (color) on the adopted
dots stored in the buffer of the picture drawing processor 5 is
transmitted to the display (unit) 8 via the color pallet(e) 6 and
via the video signal interface 7.
[0068] At this time, the dot information stored in the buffer shown
in FIG. 11(B) is transmitted at a dot rate (dot/sec.) of the
display 8 for one line as shown in FIG. 11(A).
[0069] At a step S5, the picture drawing processor 5 confirms
whether the scrolling operation from the operation keyboard 3
(keyboard) is ended. If the scrolling operation is ended (Yes), the
routine goes to a step S6. If not ended (No) at the step S5, the
routine goes to a step S8. When the scrolling operation is ended at
the step S6, the display region X for the bird's eye view on the
plan view formed road map mesh is coordinate transformed into the
bird's eye view. At the subsequent step S7, the coordinate
transformed bird's eye view is drawn on the display unit 8. In
other words, upon the end of the scroll, the bird's eye view is
again drawn with the plan view formed road map coordinate
transformed. A user friendly bird's eye view (easily recognizable)
can be displayed and the information such as a character or symbol
can also be displayed.
[0070] On the other hand, when the scrolling operation is
continued, at the step S8, the picture drawing processor 5
determines whether the display region X for the bird's eye view
overflows the predetermined region L described above. If the
overflow occurs at the step S8, the routine returns to the step S1
to update the plan view formed road map mesh on the V-RAM 10. If
the overflow does not occur, the routine returns to a step S2 so as
to determine the display region X for the bird's eye view.
[0071] The V-RAM having a considerably large memory capacity is
required in order to draw the plan view formed road map having a
considerably wider range K than the display region X for the bird's
eye view as shown in FIG. 8. Hence, a modification of the preferred
embodiment which can use the V-RAM having a relatively low capacity
will be described below.
[0072] The road map display in the form of the bird's eye view is
such that as the distance from the predetermined point of display
reference (namely, the present position of the vehicle) to a
position to be viewed from the displayed bird's eye view becomes
long, namely, as a viewing position becomes far away from the
present position, an actual display area per unit area on the
display screen becomes wider. Hence, many roads and characters are
displayed with high density in a narrower region as it becomes far
way from the predetermined point of display reference. Hence, in
order to secure a visibility in the case of the bird's eye view,
the kind of information is reduced as the viewed position becomes
far away. Specifically, the scale of reduction on the bird's eye
view based plan view formed road map mesh is varied.
[0073] In the modification, as shown in FIG. 12, the display region
X for the bird's eye view is divided into, e.g., three (display
region), the plan view formed road map mesh piece having the scale
of reductions respectively corresponding to the respective divided
regions are basic road maps. That is to say, the basic road map
mesh piece having the most detailed road map information contained
scale of reduction (lowest scale of reduction) is used for one of
the divided display regions surrounding the predetermined point of
display reference (present position), the basic road map mesh piece
having the intermediate scale of reduction is used for a second one
(a center area) of the divided display regions, and the road map
mesh piece having the most widest area indicating scale of
reduction (highest scale of reduction) is used for another third
one of the divided display regions on the upper part of the display
screen, as shown in FIG. 12. Then, as shown in FIG. 13, the dot
pattern is set for each divided region and the omitting (dot
adopted and dot unadopted) process described above is carried out.
The omitted dot processed road map mesh pieces are drawn for the
respective divided regions.
[0074] According to this modification method, the display region is
an addition of the display region corresponding to the three
divided display regions. Hence, since the display region is the
modification shown in FIG. 13 becomes smaller than the case wherein
only the most detailed information contained basic road map mesh as
in the case of the preferred embodiment is used, the capacity of
the V-RAM can be reduced and the data quantity of the plan view
formed road map mesh read from the CD-ROM 14 can be reduced and the
drawing process of the plan view formed road map mesh can be
relieved.
[0075] As described above, although the drawing process according
to the dot adopted and unadopted method is carried out during the
scroll operation on the display (image) screen, the drawing process
according to the above-described method may be carried out during
the execution time other than the scroll process. In this case,
after the drawing process is carried out for the road map mesh
containing the lines and/or polygons, the information of the
character and symbol is drawn without the dot omitting process (dot
adopted and unadopted method described above) on the drawn road map
mesh.
[0076] Although, in the embodiment, the road map information is
processed according to the dot adopted and unadopted method in a
unit of the dots, i.e., in a unit of the pixels, the drawing of the
bird's eye view may be carried out by setting the coordinates on
the plan view formed road map mesh corresponding to the respective
pixles on the display screen and by extracting only the road map
information on the set coordinates.
[0077] Furthermore, the number of the divided display regions on
the display screen and the dividing method are not limited to the
modification of the preferred embodiment described above.
[0078] It is noted that the method for executing the coordinate
transformation of the plan view formed road map mesh into the
bird's eye view (perspective projection representation) after the
scrolling operation described in the embodiment shown in FIG. 7 is
exemplified by the U.S. patent application Ser. No. 08/384,715
(attorney docket No. 305-472), (the content of the disclosure of
which being herein incorporated by reference). It is finally noted
that the navigating apparatus for the mobile body such as a vehicle
to which the present invention is applicable is exemplified by the
same U.S. patent application identified above.
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