U.S. patent application number 11/007834 was filed with the patent office on 2005-04-28 for system and method for estimating impedance time through a road network.
This patent application is currently assigned to GARMIN LTD., a Cayman Islands corporation. Invention is credited to Beesley, Darin J., Childs, Michael.
Application Number | 20050090976 11/007834 |
Document ID | / |
Family ID | 31886122 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050090976 |
Kind Code |
A1 |
Beesley, Darin J. ; et
al. |
April 28, 2005 |
System and method for estimating impedance time through a road
network
Abstract
A method and apparatus are provided for estimating an impedance
through a node at an intersection between roads in a roadway
network. The impedance may be measured in time or distance, for
example. Characteristic information describes at least one feature
of the intersecting roads. One or more pieces of characteristic
information may impact the impedance of traffic through an
intersection and are used to estimate the impedance through the
node. Examples of characteristic information are speed information,
road-type, network routing level, intersection angle information,
one-way, and cross traffic turn information. An impedance factor,
or a cost, is assigned to each piece of characteristic information.
The cost may be positive if the characteristic information adds
impedance to the node, or negative if the characteristic
information subtracts impedance from the node.
Inventors: |
Beesley, Darin J.; (Overland
Park, KS) ; Childs, Michael; (Olathe, KS) |
Correspondence
Address: |
Devon A. Rolf
GARMIN INTERNATIONAL, INC.
1200 East 151th Street
Olathe
KS
66062
US
|
Assignee: |
GARMIN LTD., a Cayman Islands
corporation
|
Family ID: |
31886122 |
Appl. No.: |
11/007834 |
Filed: |
December 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11007834 |
Dec 8, 2004 |
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10660835 |
Sep 12, 2003 |
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6856893 |
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10660835 |
Sep 12, 2003 |
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10015152 |
Dec 11, 2001 |
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6704645 |
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Current U.S.
Class: |
701/533 ;
340/995.12 |
Current CPC
Class: |
G08G 1/096811 20130101;
G08G 1/096838 20130101; G01C 21/32 20130101; G08G 1/096883
20130101 |
Class at
Publication: |
701/209 ;
701/213; 340/995.12 |
International
Class: |
G01C 021/30; G08G
001/123 |
Claims
1. A navigation system comprising: a server including--a storage
unit holding a data structure having data indicative of roads in a
roadway network and intersections of the roads at nodes, a route
calculation module calculating a planned route over the roadway
network between source and destination locations based on the data
structure held in the storage unit, and a correction module for
identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network route
that, while reducing an overall distance traveled by the planned
route, are to be avoided in the planned route between the source
and destination; and a navigation device operable to transmit the
locations to the server and receive the route from the server over
a communications link.
2. The system as set forth in claim 1, wherein the route
calculation module avoids the undesirable shortcuts.
3. The system as set forth in claim 1, wherein the correction
module identifies ramp shortcuts along an exit ramp and entrance
ramp of a road.
4. The system as set forth in claim 3, wherein the route
calculation module avoids the ramp shortcuts.
5. The system as set forth in claim 1, wherein the correction
module identifies neighborhood shortcuts through residential roads
in the roadway network where the residential roads do not directly
connect with either one of the source and destination
locations.
6. The system as set forth in claim 5, wherein the route
calculation module avoids the neighborhood shortcuts.
7. The system as set forth in claim 1, wherein the correction
module includes a neighborhood progression module identifying when
the planned route travels along residential roads located remote
from the source and destination locations.
8. The system as set forth in claim 7, wherein the route
calculation module updates the route to avoid residential roads
that are remote from the source and destination locations based on
neighborhood information received from the neighborhood progression
module.
9. The system as set forth in claim 1, wherein the route
calculation module adds one of a distance and time penalty to
potential routes that include at least one of exit/entrance ramp
shortcuts and neighborhood shortcuts.
10. The system as set forth in claim 1, the device including--a
global positioning system (GPS) receiver for receiving signals
transmitted from a plurality of GPS satellites; and a processor for
calculating, by triangulation, a position of the device using the
signals.
11. The system as set forth in claim 10, wherein the processor
determines the source location using the signals and a user
provides the destination location using an input.
12. The system as set forth in claim 10, wherein the device further
includes a display for displaying the route.
13. A navigation system comprising: a server including--a storage
unit holding a data structure having data indicative of roads in a
roadway network and intersections of the roads at nodes, a route
calculation module calculating a planned route over the roadway
network between source and destination locations based on the data
structure held in the storage unit, the route calculation module
avoiding the ramp shortcuts, and a correction module for
identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network that,
while reducing an overall distance traveled by the planned route,
are to be avoided in the planned route between the source and
destination locations, the correction module identifying ramp
shortcuts along an exit ramp and entrance ramp of a road, the route
calculation module avoiding the undesirable shortcuts; and a
navigation device operable to transmit the geographic locations to
the server and receive the route from the server over a
communications link.
14. The system as set forth in claim 13, the device including--a
global positioning system (GPS) receiver for receiving signals
transmitted from a plurality of GPS satellites; and a processor for
calculating, by triangulation, a position of the device using the
signals.
15. The system as set forth in claim 14, wherein the processor
determines the source location using the signals and a user
provides the destination location using an input.
16. A navigation system comprising: a server comprising: a storage
unit holding a data structure having data indicative of roads in a
roadway network and intersections of the roads at nodes, a route
calculation module calculating a planned route over the roadway
network between source and destination locations based on the data
structure held in the storage unit, and a correction module for
identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network that,
while reducing an overall distance traveled by the planned route,
are to be avoided in the planned route between the source and
destination locations, the route calculation module avoiding the
undesirable shortcuts, the correction module identifying
neighborhood shortcuts through residential roads in the roadway
network where the residential roads do not directly connect with
either one of the source and destination locations, the route
calculation module avoiding the neighborhood shortcuts; and a
navigation device operable to transmit the locations to the server
and receive the route from the server over a communications
link.
17. The system as set forth in claim 16, the device including--a
global positioning system (GPS) receiver for receiving signals
transmitted from a plurality of GPS satellites; and a processor for
calculating, by triangulation, a position of the device using the
signals.
18. The system as set forth in claim 17, wherein the processor
determines the source location using the signals and a user
provides the destination location using an input.
19. A navigation system comprising: a server including--a storage
unit holding a data structure having data indicative of roads in a
roadway network and intersections of the roads at nodes, a route
calculation module calculating a planned route over the roadway
network between source and destination locations based on the data
structure held in the storage unit, and a correction module for
identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network that,
while reducing an overall distance traveled by the planned route,
are to be avoided in the planned route between the source and
destination locations, the route calculation module avoiding the
undesirable shortcuts, wherein the correction module includes a
neighborhood progression module identifying when the planned route
travels along residential roads located remote from the source and
destination locations, the route calculation module updating the
route to avoid residential roads that are remote from the source
and destination locations based on neighborhood information
received from the neighborhood progression module; and a navigation
device operable to transmit the locations to the server and receive
the route from the server over a communications link.
20. The system as set forth in claim 19, the device including--a
global positioning system (GPS) receiver for receiving signals
transmitted from a plurality of GPS satellites; and a processor for
calculating, by triangulation, a position of the device using the
signals.
21. The system as set forth in claim 20, wherein the processor
determines the source location using the signals and a user
provides the destination location using an input.
22. A navigation system comprising: a server including--a storage
unit holding a data structure having data indicative of roads in a
roadway network and intersections of the roads at nodes, a route
calculation module calculating a planned route over the roadway
network between source and destination locations based on the data
structure held in the storage unit, and a correction module for
identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network that,
while reducing an overall distance traveled by the planned route,
are to be avoided in the planned route between the source and
destination, the route calculation module avoiding the undesirable
shortcuts, wherein the route calculation module adds one of a
distance and time penalty to potential routes that include at least
one of exit/entrance ramp shortcuts and neighborhood shortcuts; and
a navigation device operable to transmit the locations to the
server and receive the route from the server over a communications
link.
23. The system as set forth in claim 22, the device including--a
global positioning system (GPS) receiver for receiving signals
transmitted from a plurality of GPS satellites; and a processor for
calculating, by triangulation, a position of the device using the
signals.
24. The system as set forth in claim 23, wherein the processor
determines the source location using the signals and a user
provides the destination location using an input.
25. A navigation server for calculating a route between source and
destination locations and transmitting the route to a portable
navigation device for navigating the route, the server comprising:
a storage unit holding a data structure having data indicative of
roads in a roadway network and intersections of the roads at nodes;
a route calculation module calculating the route over the roadway
network between the source and destination locations based on the
data structure held in the storage unit, the route calculation
module avoiding the ramp shortcuts; and a correction module for
identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network that,
while reducing an overall distance traveled by the route, are to be
avoided in the route between the source and destination locations,
the correction module identifying ramp shortcuts along an exit ramp
and entrance ramp of a road, the route calculation module avoiding
the undesirable shortcuts.
26. The server as set forth in claim 25, wherein the server
transmits the route to the device over a wireless communications
network.
27. The server as set forth in claim 25, wherein the server
receives the source and destination locations from the device over
a wireless communications network.
28. The server as set forth in claim 25, wherein the device
includes--a global positioning system (GPS) receiver for receiving
signals transmitted from a plurality of GPS satellites; a processor
for calculating, by triangulation, the source location using the
signals; an input for receiving the destination location from a
user; and a display for displaying the route.
29. The server as set forth in claim 28, wherein the server also
transmits to the device a map displaying the route.
30. A portable navigation device for navigating a route between
source and destination locations, the device comprising: a global
positioning system (GPS) receiver for receiving signals transmitted
from a plurality of GPS satellites; a processor for calculating, by
triangulation, the source location using the signals; an input for
receiving indication of the destination location from a user; a
display for displaying the route between the source and destination
locations; and a transceiver for receiving the route from a
server.
31. The device as set forth in claim 30, wherein the server
receives the source and destination locations from the device over
a wireless communications network, calculates the route between the
source and destination locations, and transmits the route to the
device over the network.
32. The device as set forth in claim 30, wherein the server
includes--a storage unit holding a data structure having data
indicative of roads in a roadway network and intersections of the
roads at nodes; a route calculation module calculating the route
over the roadway network between the source and destination
locations based on the data structure held in the storage unit, the
route calculation module avoiding the ramp shortcuts; and a
correction module for identifying undesirable shortcuts
constituting predefined paths along the roads and through the nodes
in the roadway network that, while reducing an overall distance
traveled by the route, are to be avoided in the route between the
source and destination locations, the correction module identifying
ramp shortcuts along an exit ramp and entrance ramp of a road, the
route calculation module avoiding the undesirable shortcuts.
33. The device as set forth in claim 30, wherein the server also
transmits to the device a map displaying the route.
34. A navigation server for calculating a route between source and
destination locations and transmitting the route to a portable
navigation device for navigating the route, the server comprising:
a storage unit holding a data structure having data indicative of
roads in a roadway network and intersections of the roads at nodes;
a route calculation module calculating the route over the roadway
network between the source and destination locations based on the
data structure held in the storage unit; and a correction module
for identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network that,
while reducing an overall distance traveled by the route, are to be
avoided in the route between the source and destination locations,
the route calculation module avoiding the undesirable shortcuts,
the correction module identifying neighborhood shortcuts through
residential roads in the roadway network where the residential
roads do not directly connect with either one of the source and
destination locations, the route calculation module avoiding the
neighborhood shortcuts.
35. The server as set forth in claim 34, wherein the server
transmits the route to the device over a wireless communications
network.
36. The server as set forth in claim 34, wherein the server
receives the source and destination locations from the device over
a wireless communications network.
37. The server as set forth in claim 34, wherein the device
includes--a global positioning system (GPS) receiver for receiving
signals transmitted from a plurality of GPS satellites; a processor
for calculating, by triangulation, the source location using the
signals; an input for receiving the destination location from a
user; and a display for displaying the route.
38. The server as set forth in claim 37, wherein the server also
transmits to the device a map displaying the route.
39. A portable navigation device for navigating a route between
source and destination locations, the device comprising: a global
positioning system (GPS) receiver for receiving signals transmitted
from a plurality of GPS satellites; a processor for calculating, by
triangulation, the source location using the signals; an input for
receiving indication of the destination location from a user; a
display for displaying the route between the source and destination
locations; and a transceiver for receiving the route from a
server.
40. The device as set forth in claim 39, wherein the server
receives the source and destination locations from the device over
a wireless communications network, calculates the route between the
source and destination locations, and transmits the route to the
device over the network.
41. The device as set forth in claim 39, wherein the server
includes--a storage unit holding a data structure having data
indicative of roads in a roadway network and intersections of the
roads at nodes; a route calculation module calculating the route
over the roadway network between the source and destination
locations based on the data structure held in the storage unit; and
a correction module for identifying undesirable shortcuts
constituting predefined paths along the roads and through the nodes
in the roadway network that, while reducing an overall distance
traveled by the route, are to be avoided in the route between the
source and destination locations, the route calculation module
avoiding the undesirable shortcuts, the correction module
identifying neighborhood shortcuts through residential roads in the
roadway network where the residential roads do not directly connect
with either one of the source and destination locations, the route
calculation module avoiding the neighborhood shortcuts.
42. The device as set forth in claim 39, wherein the server also
transmits to the device a map displaying the route.
43. A navigation server for calculating a route between source and
destination locations and transmitting the route to a portable
navigation device for navigating the route, the server comprising:
a storage unit holding a data structure having data indicative of
roads in a roadway network and intersections of the roads at nodes;
a route calculation module calculating the route over the roadway
network between the source and destination locations based on the
data structure held in the storage unit; and a correction module
for identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network that,
while reducing an overall distance traveled by the route, are to be
avoided in the route between the source and destination locations,
the route calculation module avoiding the undesirable shortcuts,
wherein the correction module includes a neighborhood progression
module identifying when the planned route travels along residential
roads located remote from the source and destination locations, the
route calculation module updating the route to avoid residential
roads that are remote from the source and destination locations
based on neighborhood information received from the neighborhood
progression module.
44. The server as set forth in claim 43, wherein the server
transmits the route to the device over a wireless communications
network.
45. The server as set forth in claim 43, wherein the server
receives the source and destination locations from the device over
a wireless communications network.
46. The server as set forth in claim 43, wherein the device
includes--a global positioning system (GPS) receiver for receiving
signals transmitted from a plurality of GPS satellites; a processor
for calculating, by triangulation, the source location using the
signals; an input for receiving the destination location from a
user; and a display for displaying the route.
47. The server as set forth in claim 46, wherein the server also
transmits to the device a map displaying the route.
48. A portable navigation device for navigating a route between
source and destination locations, the device comprising: a global
positioning system (GPS) receiver for receiving signals transmitted
from a plurality of GPS satellites; a processor for calculating, by
triangulation, the source location using the signals; an input for
receiving indication of the destination location from a user; a
display for displaying the route between the source and destination
locations; and a transceiver for receiving the route from a
server.
49. The device as set forth in claim 48, wherein the server
receives the source and destination locations from the device over
a wireless communications network, calculates the route between the
source and destination locations, and transmits the route to the
device over the network.
50. The device as set forth in claim 48, wherein the server
includes--a storage unit holding a data structure having data
indicative of roads in a roadway network and intersections of the
roads at nodes; a route calculation module calculating the route
over the roadway network between the source and destination
locations based on the data structure held in the storage unit; and
a correction module for identifying undesirable shortcuts
constituting predefined paths along the roads and through the nodes
in the roadway network that, while reducing an overall distance
traveled by the route, are to be avoided in the route between the
source and destination locations, the route calculation module
avoiding the undesirable shortcuts, wherein the correction module
includes a neighborhood progression module identifying when the
planned route travels along residential roads located remote from
the source and destination locations, the route calculation module
updating the route to avoid residential roads that are remote from
the source and destination locations based on neighborhood
information received from the neighborhood progression module.
51. The device as set forth in claim 48, wherein the server also
transmits to the device a map displaying the route.
52. A navigation server for calculating a route between source and
destination locations and transmitting the route to a portable
navigation device for navigating the route, the server comprising:
a storage unit holding a data structure having data indicative of
roads in a roadway network and intersections of the roads at nodes;
a route calculation module calculating the route over the roadway
network between the source and destination locations based on the
data structure held in the storage unit; and a correction module
for identifying undesirable shortcuts constituting predefined paths
along the roads and through the nodes in the roadway network that,
while reducing an overall distance traveled by the route, are to be
avoided in the route between the source and destination, the route
calculation module avoiding the undesirable shortcuts, wherein the
route calculation module adds one of a distance and time penalty to
potential routes that include at least one of exit/entrance ramp
shortcuts and neighborhood shortcuts.
53. The server as set forth in claim 52, wherein the server
transmits the route to the device over a wireless communications
network.
54. The server as set forth in claim 52, wherein the server
receives the source and destination locations from the device over
a wireless communications network.
55. The server as set forth in claim 52, wherein the device
includes--a global positioning system (GPS) receiver for receiving
signals transmitted from a plurality of GPS satellites; a processor
for calculating, by triangulation, the source location using the
signals; an input for receiving the destination location from a
user; and a display for displaying the route.
56. The server as set forth in claim 55, wherein the server also
transmits to the device a map displaying the route.
57. A portable navigation device for navigating a route between
source and destination locations, the device comprising: a global
positioning system (GPS) receiver for receiving signals transmitted
from a plurality of GPS satellites; a processor for calculating, by
triangulation, the source location using the signals; an input for
receiving indication of the destination location from a user; a
display for displaying the route between the source and destination
locations; and a transceiver for receiving the route from a
server.
58. The device as set forth in claim 57, wherein the server
receives the source and destination locations from the device over
a wireless communications network, calculates the route between the
source and destination locations, and transmits the route to the
device over the network.
59. The device as set forth in claim 57, wherein the server
includes--a storage unit holding a data structure having data
indicative of roads in a roadway network and intersections of the
roads at nodes; a route calculation module calculating the route
over the roadway network between the source and destination
locations based on the data structure held in the storage unit; and
a correction module for identifying undesirable shortcuts
constituting predefined paths along the roads and through the nodes
in the roadway network that, while reducing an overall distance
traveled by the route, are to be avoided in the route between the
source and destination, the route calculation module avoiding the
undesirable shortcuts, wherein the route calculation module adds
one of a distance and time penalty to potential routes that include
at least one of exit/entrance ramp shortcuts and neighborhood
shortcuts.
60. The device as set forth in claim 57, wherein the server also
transmits to the device a map displaying the route.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation and claims priority
benefit of U.S. patent application Ser. No. 10/660,835, filed Sep.
12, 2003, which is a continuation and claims priority benefit of
U.S. patent application Ser. No. 10/015,152, filed Dec. 11, 2001,
now U.S. Pat. No. 6,704,645 B1, issued Mar. 9, 2004. The identified
earlier-filed applications are hereby incorporated into the present
application.
BACKGROUND OF THE INVENTION
[0002] Certain embodiments of the present invention relate to
navigational route planning. In particular, certain embodiments of
the present invention relate to determining a route through a road
network.
[0003] Route planning devices are well known in the field of
navigational instruments. Several algorithms utilized by planning
devices calculate the route from one of the source and/or
destination locations or from both simultaneously. Conventional
planning algorithms operate based on a predefined stored data
structure including data indicative of a geographic region
containing the source and destination locations.
[0004] Some devices implement a straight line approach in
determining the distance between source and destination locations.
In the straight line approach, the processor creates a straight
line from the present location to the final destination and
measures that straight line distance. For example, if a desired
destination is on a mountain, the straight line distance from a
current location might be only six miles. However, if the only
available road to that destination is a windy road around the
mountain entailing 30 miles of actual driving, the route planning
distance calculated by the straight line approach will be
inaccurate.
[0005] Other devices implement a nodal analysis in which a number
of potential paths are determined from a present location to a
destination location based on stored data indicative of roadways
between nodes. The nodal analysis then examines each potential path
and determines an impedance or "cost" associated with each path
(i.e. a measure of the amount of time or distance required to
travel the path). Paths are eliminated based on criteria such as
shortest distance, shortest time, lowest cost, or user inputted
preferred routes.
[0006] However, conventional route planning devices will not find
the most efficient route since they do not take into consideration
certain factors that affect travel over a particular route. For
example, a user may input desired source and destination locations,
and request the route that covers the shortest distance. While only
one particular route may be the physically shortest distance
between source and destination locations, other near-shortest
routes may exist that are only slightly longer. The shortest and
near-shortest routes include travel along different combinations of
roads and travel through unique combinations of road intersections.
Each road in the shortest and near-shortest routes has an
associated travel speed, representing the speed limit or range at
which traffic typically travels over the road. Also, each road in
the shortest and near-shortest routes passes through a combination
of intersections. The shortest and near-shortest routes may be
close in length, while the shortest route may include roads with
slower travel speeds and/or more intersections and/or intersections
that typically require more time (e.g., stop signs, stop lights,
crossing larger/busier highways, turning across traffic onto a new
road, etc.) as compared to one or more near-shortest routes.
[0007] Conventional route planning devices produce a shortest
distance route which includes roads that are selected independent
of whether the roads have slower traveling speeds. Conventional
route planning devices do not include travel-time information for
road intersections, nor account for delays at road intersections
when planning a route. Although one route represents the shortest
distance, a more efficient route may exist with a slightly longer
distance (e.g., a near-shortest distance route). The difference
between the length of the shortest distance route and the
near-shortest distance route may be insignificant. Consequently,
the user may travel for a longer period of time and encounter more
traffic delays by taking the shortest distance route.
[0008] Conventional route planning devices do not take into
consideration travel delays experienced at intersections, such as
delays due to stop signs, stop lights, crossing lanes of on-coming
traffic, turning onto or off of one-way roads, the angle at which
roads intersect when a route turns from one road onto another, and
the like. This is not desirable.
[0009] Thus, a need has long existed in the industry for a method
and apparatus for determining impedance time through a road network
that addresses the problems noted above and other problems
previously experienced.
BRIEF SUMMARY OF THE INVENTION
[0010] Certain embodiments of the present invention relate to a
method for estimating an impedance time through a node at an
intersection between roads in a roadway network. The method
includes identifying characteristic information that describes at
least one feature of the intersecting roads. Based on the
characteristic information, an impedance time associated with
potential delays by traffic traveling through the node is
estimated. The characteristic information may include speed
information, such as speed categories or speed bands. A speed band
identifies a speed range in which traffic travels on the road, and
a speed differential between the speed bands of intersecting roads
may be determined. Optionally, the characteristic information may
include road-type or network routing level information, such as
when the roadway network is divided into a hierarchy of road-types.
A route level may be assigned to each road intersecting at a node,
and a route level differential between the route levels of the
roads may be determined. The characteristic information may include
intersection angle information and/or cross traffic turn
information.
[0011] In another embodiment of the present invention, a method is
provided for calculating a navigation route between first and
second geographic locations through a roadway network of roads that
intersect at nodes. A data structure is provided that has data
indicative of the roadway network of roads. The data includes
feature data indicating traffic characteristics for the roads.
Route impedance is calculated for a navigation route through the
roadway between the first and second locations based on the feature
data. The node impedance is determined for the navigation route
where the navigation route intersects other roads. The node
impedance may indicate a potential delay that traffic experiences
when traveling through a node. The node impedance and route
impedance are used to calculate the navigation route. The node and
route impedances may be measured in time or distance.
[0012] The feature data may include speed information, one-way,
and/or intersection angle information. A turn penalty may be
assigned when the navigation route crosses on-coming traffic.
Optionally, a neighborhood penalty may be added to the node or
route impedance when the navigation route travels through
residential areas that are not located at the first and second
geographic locations. Optionally, an exit/entry ramp penalty may be
added to the node or route impedance when the navigation route
travels along an exit ramp from a first road directly onto an entry
ramp back onto the first road.
[0013] In another embodiment of the present invention, a navigation
device is provided comprising a memory and processor. The memory at
least temporarily stores at least a portion of a data structure
having data indicative of a roadway network of roads intersecting
at nodes. The data structure includes feature data of traffic
characteristics for roads. The processor accesses the memory and
calculates a route through the roadway network between geographic
locations from the data stored in the data structure. The processor
estimates node impedances for intersection nodes, and utilizes the
route impedance and node impedance to calculate the route. The
feature data may include speed information, road-type information,
routing level information, intersection angle information, and/or
cross traffic information which is used to calculate node
impedance. Optionally, the device may include an input buffer for
temporarily storing a portion of the data structure received from
an external storage device. In one embodiment, the device includes
a display that presents the route to an operator. The device may
also comprise a wireless input/output unit used to communicate with
an external network and receive a portion of the data structure of
a wireless connection with the external network.
[0014] In another embodiment of the present invention, a navigation
system is provided comprising a storage unit, a route calculation
module, and a correction module. The storage unit stores a data
structure having data indicative of roads and intersection nodes in
a roadway network. The data includes road-type information that
classifies roads into a hierarchy of route levels. The route
calculation module calculates a planned route between source and
destination locations over the network based on the stored data.
The route calculation module may calculate the route based on a
shortest distance routing algorithm, and may add a distance penalty
to potential routes that include an exit or entrance ramp. The
correction module identifies undesirable shortcuts by using the
road-type information to avoid traveling from a road of a higher
route level to a road of a lower route level. Undesirable shortcuts
may be along exit and entrance ramps of a road or through
neighborhoods. Optionally, the correction module may include a
neighborhood progression module that updates the route to avoid
residential roads that are remote from the source and destination
locations.
[0015] The route calculation module may receive a request from a
mobile unit over a network to calculate a route. The request would
include source and destination locations, and other use specific
information. The route calculation module would access
corresponding data structures, such as in a server, plan the route,
and return the planned route to the mobile unit. The returned
information would include the portion of the roadway network
between the source and destination locations. The network may be
the internet, a wireless connection and the like.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
[0016] FIG. 1 illustrates a block diagram of a navigation device
formed in accordance with an embodiment of the present
invention.
[0017] FIG. 2 illustrates a front view of a navigation device
formed in accordance with an embodiment of the present
invention.
[0018] FIG. 3 illustrates a block diagram of a navigation device
formed in accordance with an embodiment of the present
invention.
[0019] FIG. 4 illustrates a navigation system formed in accordance
with an embodiment of the present invention.
[0020] FIG. 5 illustrates a roadway network formed in accordance
with an embodiment of the present invention.
[0021] FIG. 6 illustrates a flow chart of a method for estimating
the impedance time through an intersection node in accordance with
an embodiment of the present invention.
[0022] FIG. 7 illustrates a flow chart of a method for estimating
turn penalties in accordance with an embodiment of the present
invention.
[0023] FIG. 8 illustrates a flow chart of a method for improving
shortest distance routes in accordance with an embodiment of the
present invention.
[0024] The foregoing summary, as well as the following detailed
description of the preferred embodiments of the present invention,
will be better understood when read in conjunction with the
appended drawings. For the purpose of illustrating the invention,
there is shown in the drawings, embodiments which are presently
preferred. It should be understood, however, that the present
invention is not limited to the precise arrangements and
instrumentality shown in the attached drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0025] FIG. 1 illustrates a system 10 formed in accordance with an
embodiment of the present invention. The system 10 includes at
least one processor 12 for carrying out various processing
operations discussed below in more detail. The processor 12 is
connected to a cartographic database 14, memory 16, a display 18, a
keyboard 20, and a buffer 22. Optionally, more than one processor
12 may be included. The cartographic database 14 may store data
indicative of a roadway network (in full or in part) used in
connection with embodiments of the present invention. The memory
16, while illustrated as a single block, may comprise multiple
discrete memory locations and/or discs for storing various types of
routines and data utilized and/or generated by embodiments of the
present invention. The buffer 22 represents a memory storage area
that may be within memory 16 or separate therefrom. Buffer 22 is
used to temporarily store data and/or routines used in connection
with embodiments of the present invention. The display 18 displays
information to the user in an audio and/or video format. The
keyboard 20 permits the user to input information, instructions and
the like to the processor 12 during operation.
[0026] By way of example only, initial operations may be carried
out by an operator of the system 10, utilizing the keyboard 20 for
controlling the processor 12 in the selection of parameters,
defining data structures to be developed and/or accessed, and the
like.
[0027] The data structure(s) stored in the cartographic database
14, memory 16, and/or buffer 22 may include data indicative of
features associated with a roadway network and/or a geographic
area. The data may represent points, lines, areas, coordinates
(longitude, latitude and altitude), or otherwise. For instance,
portions of a highway, river or boundary (e.g., a state or country
boundary), trails and the like may be represented by linear
features stored in the data structure. In addition, cities, towns,
neighborhoods, communities and the like may be represented by point
features within the data structure. Also, buildings, lakes, and the
like may be represented by area features. Prior to storage, various
common features may be identified for cartographic data and such
common features may be classified based upon predefined
hierarchies. For example, interstate highways may be defined and/or
organized as one feature class, state highways and roads may be
defined as a second feature class, and county roads may be defined
as a third feature class. Features other than roads, such as rivers
and waterways, may also be classified. As a further example,
geographic boundaries (e.g., state and county lines) may be
assigned one or more different feature classes.
[0028] FIG. 2 illustrates a portable electronic device 30 formed in
accordance with an embodiment of the present invention. The
electronic device 30 is oriented along a vertical axis (as
illustrated) or horizontal axis when held by a user. The portable
electronic device 30 includes a housing 32 having a face plate 34
and sidewalls and a back wall (not shown). The portable electronic
device 30 further includes an antenna 36 mounted at one corner of
the housing 32. The face plate 34 is substantially rectangular in
shape. The face plate 34 securely frames the display screen 38 and
houses the control panel 40. The control panel 40 includes several
push button-type keys 42 that afford the user control over the
portable electronic device 30.
[0029] Optionally, a directional toggle pad 44 may be included
within the control panel 40. In one application, such as when
utilizing the portable electronic device 30 within a global
positioning system, the toggle pad 44 affords the ability to scan
through a large map of a geographic area, all or a portion of which
is stored in memory of the portable electronic device 30. The
portable electronic device 30 then displays portions of the scanned
map on the display screen 38. The display screen 38 also
illustrates planned routes through geographic areas between source
and destination locations. Optionally, the control panel 40 may
include a speaker/microphone combination, designated by reference
numeral 46, to afford communication between the operator and a
remote destination.
[0030] The display screen 38 may be located below the control panel
40 (when oriented along a vertical axis) to afford easy data entry
by the user. When vertically oriented, the display screen 38 is
controlled to orient data upon the display screen 38 such that side
48 of the display screen 38 represents the top of the data to be
displayed, while side 50 of the display screen 38 represents the
bottom. Thus, the data is preferably displayed from the top 48 to
the bottom 50 of the display screen 38.
[0031] FIG. 3 illustrates a block diagram for an electronic circuit
of the portable electronic device 30 formed in accordance with an
embodiment of the present invention. The electronic circuit
includes a processor 52 that communicates via the control panel 40
through line 41. The processor 52 communicates via line 39 with the
display screen 38. The electronic circuit further includes a memory
54 that is accessed by the processor 52 via line 53. The antenna 36
is connected to the processor 52 via a cellular
transmitter/receiver 37 and a GPS receiver 35. The electronic
circuitry of the portable electronic device 30 is powered by a
power supply (not shown) housed within the device or connected
thereto. A microphone 33 and a speaker 31 are also connected to,
and communicate with, the processor 52.
[0032] The housing 32 of the portable electronic device 30 houses
the processor 52, memory 54, display 38 and key pad 40. The display
screen 38 and control panel 40 are accessible at the exterior of
the housing. In one embodiment, the portable electronic device 30
is utilized in conjunction with a global positioning system for
acquiring signals transmitted from satellites in geosynchronous
orbit. In such an embodiment, the processor 52 includes means for
calculating, by triangulation, the position of the portable
electronic device 30. In such an embodiment, an image file
indicative of a selected map is held in memory 54. In accordance
with one embodiment, the image file held in memory 54 comprises
spatial data indices according to a data structure defining a
geographic area of interest.
[0033] An operator of the portable electronic device 30 controls
the processor 52 through use of control panel 40 to display map
images on the display screen 38. Utilizing the control panel 40,
the operator selects various zoom levels, corresponding to layers
of the data structure for a particular geographic region desired to
be displayed on the display screen 38. Data indicative of the map
to be displayed is accessed from the memory 54 according to the
inputs by the user using the control panel 40. When performing a
route planning operation, the operator enters a source location and
a destination location, such as by entering addresses, geographic
coordinates, well-known buildings or sites, and the like. The
processor 52 accesses data structures stored in memory 54 to
calculate a suggested route.
[0034] FIG. 4 illustrates a navigation and routing system 70 formed
in accordance with an alternative embodiment of the present
invention. The system 70 includes one or more mobile units 72
capable of performing navigation and/or routing functions, a server
74 and an intervening network 76. The mobile units 72 may each
include some or all of the structure and/or functionality of the
portable electronic device 30. The server 74 may perform a majority
of the navigation and route planning operations and transmit
results and limited geographic data to the mobile units 72.
Alternatively, the server 74 may simply perform minor management
operations. The server 74 communicates with the mobile units 72
through communications links 78 and 80 and the network 76 which may
constitute the internet, a wireless communications network
supported by ground-based towers and/or satellites, and the like.
The mobile units 72 may receive data structures, coordinate
information, and the like over communications links 78 and 80 from
the network 76.
[0035] During operation, the server 76 may simply transmit data
structures for requested geographic regions to the mobile units 72,
after which the mobile units 72 carry out all necessary processing
to perform navigation and routing operations. Alternatively, the
mobile unit 72 need not store the data structures. Instead, the
server 74 may maintain the data structures and carry out navigation
and routing calculations based upon requests received from the
mobile unit 72. For example, the user may enter source and
destination locations for a desired routing operation. The source
and destination coordinates are transmitted from the mobile unit 72
through the communications links 78 and 80 and network 76 to the
server 74 which calculates the desired route and returns such
information to the mobile unit 72. In this alternative embodiment,
the mobile unit 72 need not store large cartographic data blocks or
data structures that would otherwise be needed to calculate and
plan a route.
[0036] FIG. 5 illustrates a portion of a data structure containing
data indicative of a roadway network 200 formed in accordance with
an embodiment of the present invention. The portion of the roadway
network 200 includes roads 202-214. The roadway network 200
includes multiple types of roads, such as interstate highways,
state highways, country roads, and residential streets. The roads
202-214 intersect at intersection nodes 216-228. A segment is a
portion of a road 202-214 that is between two nodes 216-228. Nodes
at either end of a segment are adjacent. For example, segment 217
is a portion of road 214 and is between node 226 and node 228, thus
nodes 226 and 228 are adjacent to one another. The terms "adjacent
nodes" or simply "adjacencies" shall be used throughout to refer
nodes that are adjacent to one another.
[0037] FIG. 5 sets forth points A-E within the roadway network 200.
Exemplary route planning operations carried out by certain
embodiments of the present invention will be described below in
connection with roads 216-228 and points A-E.
[0038] The system 10 of FIG. 1, the portable electronic device 30
of FIG. 2 or the network of FIG. 4 may be utilized to generate a
route from a first location to a second location within the roadway
network 200. The processor 12 utilizes the data stored in the
cartographic database 14 and data input by the user through the
keyboard 20 to calculate the requested route. Optionally, the user
may enter a time of day or day of the week in which the user wishes
to travel. In this alternative embodiment, the device 30 uses the
time at which the user desires to travel to access different
characteristic information for a particular road, to account for
times of day in which a road or intersection is very busy. Although
the remaining Figures are discussed in relation to system 10, it
should be understood that the device 30 and network 76 may also be
used to perform similar functions.
[0039] Travel through the roadway network 200 is described in terms
of distance, time or user preferences (e.g., scenic routes, routes
through/around business districts, routes through/around downtown
areas and the like). The distances, times and user preferences are
generally referred to as "impedances." Route planning devices
calculate shortest distances and fastest times, and maximize user
preferences by calculating impedances for various routes based on
characteristic information describing features of the roadway
network.
[0040] As previously discussed, some cartographic data may be
classified based upon predefined hierarchies. For data such as
roads, the hierarchy may be divided into network routing levels
which are stored as characteristic data for an associated road. The
roads most desirable to use for routing may be assigned to a
relatively high network routing level, while roads least desirable
to use for routing may be assigned to a relatively low network
routing level. For example, if road 202 is an interstate highway
and road 214 is a residential road, road 202 would have a higher
network routing level than road 214 because road 202 is a more
desirable road for routing when considering factors such as speed
limit, number of lanes, and number of stop lights/signs.
[0041] Cartographic data for individual roads may also include
characteristic information representative of speed data. The speed
data may be organized into speed categories describing a range of
traveling speeds, or speed bands. Each speed band represents a
range of speed, such as 0-10 miles per hour (mph) or 11-20 mph, in
which traffic generally travels over a given road.
[0042] Optionally, a particular road may be assigned one speed band
for certain times of day (e.g., non-rush hour) and assigned a
second speed band for other times of day (e.g., rush hour). To
utilize different speed bands for a particular road, the user also
enters the time of day that the user wishes to travel. In this
instance, the route planning device takes into consideration the
time of day for traveling (if known) and selects the corresponding
speed band.
[0043] The characteristic information may also identify whether the
road is a one-way road. In FIG. 5, roads 210 and 212 are one-way
roads allowing travel in opposite directions, as indicated by the
arrows, while roads 208 and 214 allow travel in both directions.
One-way roads impact traffic by increasing or decreasing the time
necessary for travel along the road and the time generally needed
to pass through an intersection node (e.g., turn onto a one-way
road, turn off of a one-way road, or cross a one-way road). To
compensate for the impact on overall travel time, an impedance
increment is either added to or subtracted from the impedance
estimate, as further described below. The impedance increment
constitutes a time (e.g., seconds or minutes) when calculating a
travel time. The impedance increment constitutes a distance (e.g.,
feet or meters) when calculating a travel distance..
[0044] FIGS. 6, 7, and 8 illustrate exemplary methods for
determining three distinct components which may contribute to the
estimated impedance value through a node of a navigable roadway
network. FIG. 6 illustrates a method for estimating impedance
factors due to speed band and route level changes experienced by a
path through an intersection. FIG. 7 illustrates a method for
establishing impedance factors associated with a turn that is to be
made through an intersection. FIG. 8 illustrates a method for
applying additional impedance values through a node to discourage a
route from being planned through certain portions of the roadway
network, as disclosed below. These components can be applied
singly, or in combination, and have the effect of producing
superior routes when compared to conventional routing
algorithms.
[0045] The processing steps illustrated by FIGS. 6-8 are part of a
larger route planning algorithm, conventionally implemented as one
of a collection of methods generally known as Greedy algorithms.
One such algorithm is the A* algorithm, but other algorithms may be
used. The algorithm may calculate the route in one direction (e.g.
from the source to the destination) or bi-directionally (e.g. from
both the source and destination).
[0046] By way of example only, one method may involve an iterative
process in which a list of nodes to be explored is continuously
analyzed and updated. The list represents a running list of nodes
to be explored. The process includes selecting, from the list, a
best node (e.g., a node having the least cost associated with it).
The selected best node is analyzed to identify its adjacency
information, namely one or more nodes adjacent to the best node.
The newly identified adjacent nodes are added to the list of nodes
to be explored. Then the costs associated with the newly added
nodes are calculated, and the list is searched to identify a new
best node (e.g., new lowest cost node). The cost assigned to a node
may include several factors, such as a cost from the originating
location of a search to the node and an estimate of cost from the
node to a final search location.
[0047] Finding a low-cost path between two points in the network
with such methods involves iteratively examining the adjacencies
emanating from the source and destination in the network,
eventually "discovering" a low-cost path. Adjacencies represent
adjacent nodes directly connected to a given node through road
segments without any intervening intersections. During the
adjacency expansion step for a given node, these algorithms
evaluate the cost or impedance to traverse from one adjacent node
through the given node, to another adjacent node. This step
evaluates all appropriate adjacency information for each "best
node" in sequence. During the evaluation of each best node, the
operations set forth in FIGS. 6-8 are applied to emulate the
real-world traversal cost experienced when passing through a given
intersection node from one adjacent road to another. A separate
traversal cost or impedance as disclosed below may be calculated
for each possible path through the intersection from adjacent
roadways. As noted above, cost or impedance values may be expressed
in terms of time, distance, or other suitable metric, and may be
tailored to the needs of a specific implementation or embodiment.
For example, a user may input data requesting the fastest or
shortest route.
[0048] FIG. 6 illustrates a flow chart of a method for estimating
the impedance through an intersection node of a navigable network
in accordance with an embodiment of the present invention. As
previously discussed, FIG. 6 may be repeated for each
adjacency.
[0049] At step 250, a base incremental impedance factor for traffic
control is set. The impedance factor may be determined by the
processor, or may be input using the keyboard 20. The impedance
factor may be any positive number, and determines the base cost of
traversing through a given node from one adjacent node to another,
effectively applying a cost penalty for going through a given road
network intersection. For example, the impedance may be expressed
in units of time, such as seconds, but the selected units and value
associated with this base impedance may vary according to the goals
of a particular implementation. The base incremental impedance is
further modified as described below.
[0050] Next, at Step 252, the processor 12 obtains characteristic
information for the roads of interest from the cartographic
database 14. The roads of interest represent the roads presently
being considered by the overall route planning algorithm. The
characteristic information may include speed information, network
routing levels, one-way road information, left and right turn
information, angle of intersection information between roads,
road-type information, and the like. The characteristic information
may include such data as whether the road is residential or in a
neighborhood. Certain characteristic information is stored in the
data structure for the associated roadway network. Other
characteristic information is generated during a route calculation
process by the overall route planning algorithm. For example, the
overall route planning algorithm identifies right and left turn
information, namely whether a potential route includes right or
left turns at a particular intersection.
[0051] At steps 254 and 258, the processor 12 emulates the effect
of stop lights, stop signs, and other common traffic control items
not conventionally provided as part of the cartographic database.
For a potential path through a given node (an inbound road and
outbound road through the intersection), the processor 12 utilizes
information about the relative difference in speed band and routing
level of the specified adjacency pair to adjust the base
incremental impedance factor of step 250.
[0052] At step 254, the processor 12 estimates the relative cost
effect of crossing roads with differing speed bands, emulating the
cost of crossing roads with higher or lower speeds. Each road in
the cartographic database 14 may be assigned a speed band. For a
given adjacency path through the intersection, the processor 12
identifies the maximum speed band to be crossed, and compares this
to the speed band of the inbound adjacent road. For example, with
reference to FIG. 5, if road 208 has been assigned a speed band of
21-30 and road 212 has been assigned a speed band of 41-54, there
typically will be an impedance cost increase associated with
passing through node 224 along road 208, because the adjacency must
cross the higher-speed road 212. The magnitude of the modification
applied to the base impedance, and the nature of the modification
may be tailored in a specific implementation, and may depend on the
number and nature of the speed information provided in the
cartographic database, and/or the relative speed band differences
between roads.
[0053] At step 256, the processor 12 increases the incremental
impedance factor established at step 250 if the selected adjacency
crosses a road with a greater speed band. If the selected adjacency
crosses a road with a lesser speed band, the processor 12 decreases
the incremental impedance factor.
[0054] At step 258, the processor 12 estimates the relative cost
effect of crossing roads with differing route levels. As explained
previously, the roadway network may be arranged in a hierarchy of
routing levels where roadway segments at a higher routing level
provide preferable pathways through a given region than those
assigned to a lower routing level. For example, it is likely that
an adjacency path along a low route level road that must cross a
higher route level road will experience impedance costs due to the
presence of a traffic control structure such as a stop sign. When a
higher route level road crosses a lower route level road, there is
a lessened probability that a significant impedance cost will be
encountered.
[0055] At step 260, the processor 12 increases the incremental
impedance factor if the selected adjacency crosses a road with a
greater route level. If the selected adjacency crosses a road with
a lower route level, the processor 12 decreases the incremental
impedance factor. The magnitude of the modification applied and the
nature of the modification may be tailored in a specific
implementation, and may depend on the number and nature of the
route levels provided in the cartographic database, and/or the
relative route level differences between roads.
[0056] At step 262, the processor 12 adjusts the estimated cost of
the potential path by a percentage of the impedance factor based on
one-way road characteristic information. The estimated cost of
crossing a one-way road at a node is weighted less because the
traffic is moving in only one direction, thus the driver crossing a
one-way road needs to monitor traffic in only one direction. The
processor 12 determines whether the road being crossed at the node
is a one-way road. In the example above, road 212 is a one-way
road, thus the estimated cost of the potential path is reduced by a
percentage of the impedance factor.
[0057] Next, at step 264, the processor 12 increases the impedance
factor if the road being crossed is not a one-way road, and
decreases the impedance factor if the road being crossed is a
one-way road. The processor 12 may then use the impedance factor of
step 264 to adjust the estimated overall cost of a potential
path.
[0058] FIG. 7 illustrates a flow chart of a method for estimating
turn penalties in accordance with an embodiment of the present
invention. The sequence set forth in FIG. 7 is carried out as part
of an overall route planning algorithm as explained previously for
FIG. 6, and may be repeated for each adjacency.
[0059] At step 270, an incremental base impedance factor for turns
is set. As with the base impedance factor set in step 250 in FIG.
6, the base impedance factor of step 270 may be determined by the
processor 12 or may be input using the keyboard 20. The base
impedance factor of step 270 may or may not be the same value
utilized in step 250. If the potential path does not include a
turn, the method of FIG. 7 may not apply for the adjacency.
[0060] At step 272, the processor 12 obtains the characteristic
information for the roads of interest from the cartographic
database 14 and from the overall route planning algorithm. The
characteristic information includes the left and right turn
information, angle-of-intersection information, road-type, and
speed information. The left and right turn information identify
whether an adjacency path through a node presently considered
includes a right turn or a left turn at the intersection node.
Additional characteristic information that may be considered is
whether the driver is driving on the left or the right side of the
road, as determined by driving convention for the region.
[0061] At step 274, the processor 12 estimates one component of the
relative cost effect of performing a turn at the intersection node
by considering the speed bands of the adjacent roadway segments
involved in the turn. At this step, a turn involving very low-speed
roads would typically apply a small increase to the base impedance
factor established at step 270, whereas a turn involving high-speed
roads would typically apply a larger increase to the base impedance
factor of step 270. This has the effect of increasing the overall
turn cost as the average speeds of the adjacent roads goes up.
[0062] Next, at step 276, the processor 12 increases the
incremental impedance factor a small amount if the turn involves
low-speed roads. It the turn involves high-speed roads, the
processor 12 increases the incremental impedance factor a larger
amount.
[0063] At step 278, the processor 12 estimates the cost of the
route based on the angle-turn factor. The angle-turn factor may be
assigned based on several components. One component is the size of
the turn angle, which is measured relative to the direction of
travel. The turn angle may be divided into bands of degrees, with
the number of degrees in each band depending upon the desired level
of courseness in the data. For example, turn angles may be divided
into 45 degree bands. Hence, a turn that is 5 degrees would be
weighted the same as a turn that is 40 degrees. A turn that is 90
degrees, however, would be weighted differently than a 40 degree
turn. For example, a 90 degree turn may be more "expensive", or
have a higher cost, than a 40 degree turn. Turns greater than 90
degrees get progressively more expensive, with a U-turn (180
degrees), being the costliest.
[0064] Another component of the angle-turn factor is the side of
the road the driver is driving on relative to the turn direction.
Driving side will be discussed first in relation to the country the
route is located in. For example, in the United States, drivers
travel in the right hand lane in the direction of travel. In
England, however, drivers travel in the left hand lane in the
direction of travel. The processor 12 identifies the lane
convention in the country of travel, and adjusts the angle-turn
factor based upon the direction of the turn. If it is necessary to
cross a lane of on-coming traffic to make a turn, the turn is more
expensive. Therefore, a left turn in England, which is made from
the left lane of the first road into the left lane of the second
road, is less expensive than a left turn in the United States,
which is made from the right lane of the first road, across at
least one lane of on-coming traffic, into the right lane of the
second road.
[0065] The reasons stated above in relation to the country also
apply when the road of travel is a one-way road. For example, a
left turn in the United States made from the left lane of a one-way
road is less expensive than a left turn made from the right lane of
a two-way road, because oncoming traffic is not present on the
one-way road.
[0066] At step 280, the processor 12 increases the incremental
impedance factor based on the angle-turn factor. At step 282, the
processor estimates the cost of the possible path based on one-way
road information. Step 282 is similar to Step 262 of FIG. 6,
wherein a percentage of the impedance factor set in Step 270 is
used to decrease the impedance factor if the driver is turning onto
a one-way road. Therefore, in the example of FIGS. 7 and 5, the
estimate of the turn at node 224 from road 208 onto road 212 may be
decreased to reflect that road 212 is a one-way road.
[0067] At step 284, the processor 12 decreases the incremental
impedance factor if the driver is turning from and/or onto a
one-way road. The processor 12 may use the impedance factor of step
284 to adjust the estimated overall cost of the potential path.
[0068] FIG. 8 illustrates a flow chart of a method for improving
shortest distance routes in accordance with an embodiment of the
present invention. When choosing the shortest distance route
between 2 points, it is possible that the shortest distance route
will include undesirable shortcuts, such as traveling through a
neighborhood when the neighborhood is not the destination or the
point of origin, or taking the exit and entry ramps of an
interstate highway rather than remaining on the highway. In
addition, traveling through a neighborhood may increase overall
travel time if the route is not significantly shorter than driving
around the neighborhood on a road with a higher network routing
level. The sequence set forth in FIG. 8 is carried out as part of
an overall route planning algorithm.
[0069] At Step 290, an incremental impedance factor for
neighborhoods is set. As the method is used to improve the shortest
distance route, the impedance factor of step 290 is measured in
distance. Therefore, the incremental impedance factor of step 290
may or may not have the same value and may or may not be defined by
the same unit of measure as the impedance factors defined in steps
250 and 270, and may be tailored to the implementation as
needed.
[0070] Next, at step 292, the processor 12 obtains characteristic
information for the roads of interest from the cartographic
database 14. Although other characteristic information may be
obtained and used by the processor 12 for other purposes, the
network routing level and road-type information is used by the
method illustrated in FIG. 8.
[0071] At step 294, the processor 12 estimates the cost of the
possible path based on routing level information. The processor 12
compares the network routing level of the roads intersecting at
each node. Referring to FIG. 5, if a route is planned from point D
to point B, the processor 12 will compare the network routing
levels of the roads at nodes 216 and 220. Traveling from point D,
the road 202 is an interstate highway and may have a network
routing level of 5. Road 204 is an exit ramp and may have a network
routing level of 3.
[0072] Next, at step 296, the processor 12 increases the impedance
factor for traveling through a node from a road with a higher
network routing level to a road with a lower network routing level.
Continuing with the above example, because the network routing
level of an exit ramp is lower than that of an interstate highway,
the processor 12 increases the incremental impedance factor set in
step 290.
[0073] If, however, a route was planned from point D to point E, it
is not advantageous to exit and immediately re-enter an interstate
highway to save a short distance. Increasing the incremental
impedance factor in step 296 for taking the exit ramp (road 204) at
node 216 may prevent the processor 12 from directing the driver off
the interstate highway (road 202) at node 216 and back onto the
interstate highway (road 202) via the entry ramp (road 206), even
if the combined distance of the entry ramp and the exit ramp is
less than the distance traveled by remaining on road 202.
[0074] At step 298, the processor 12 estimates the cost of the
possible path based on neighborhood, or residential, road
information. For example, a distance penalty is added for traveling
on road segments located in neighborhoods. The distance penalty may
be a percentage of the length of the segment (i.e. the road between
each node) such as 5%. Adding a penalty of 5% will tend to prevent
the processor 12 from planning a shortest distance route through a
neighborhood when the neighborhood is not the origin or the
destination. The penalty of 5%, however, is not a large enough
penalty to prevent the route from traveling through the
neighborhood if the neighborhood route is significantly shorter
than traveling on roads with higher network routing levels that
avoid the neighborhood.
[0075] At step 300, the processor 12 increases the incremental
impedance factor if the path travels through a neighborhood by
adding a distance penalty, as discussed previously. The processor
12 may then use the impedance factor of step 300 to adjust the
estimated overall cost of the potential path.
[0076] Correction modules that include one or more of the sets of
steps for estimating impedance time, estimating turn penalties,
and/or improving shortest distance routes by eliminating
undesirable shortcuts, such as through neighborhoods, may be
utilized by conventional planning algorithms and route planning
systems. By using the aforementioned techniques for calculating the
estimated delays that are experienced by traffic moving through a
node, a more desirable route is planned.
[0077] While particular elements, embodiments and applications of
the present invention have been shown and described, it will be
understood, of course, that the invention is not limited thereto
since modifications may be made by those skilled in the art,
particularly in light of the foregoing teachings. It is therefore
contemplated by the appended claims to cover such modifications as
incorporate those features which come within the spirit and scope
of the invention.
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