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INCORPORATION BY REFERENCE
The disclosures of the following priority applications are herein
incorporated by reference:
Japanese Patent Application No. 8-279686 filed Oct. 22, 1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a navigation system that is capable of
searching a recommended route based upon a plurality of sets of map data
at different scales and drawing the recommended route superimposed upon
display maps at different scale.
2. Description of the Related Art
Vehicular navigation systems in the known art are provided with a function
for displaying a roadmap of the area where the vehicle is currently
located, a function for accurately detecting the vehicle position through
map matching, a function for calculating a recommended route from a point
of departure to a destination and the like. In these vehicular navigation
systems in the prior art, roadmap display data, data for map matching and
data for route search are separately stored in a CD ROM in order to
maintain compatibility with existing software programs and also to improve
the processing speed.
The roadmap display data include widest range map data for displaying large
areas at the smallest scale, most detailed map data for displaying small
areas in detail at the largest scale and a plurality of sets of map data
at different scales between that of the widest range map data and that of
the most detailed map data. For instance, the widest range map data may be
referred to as level 4 data, the most detailed map data may be referred to
as level 1 data and the sets of data at scales between those of the level
4 data and the level 1 data may be referred to as level 3 data and level 2
data. In that case, the route search data include two sets of data that
correspond to the level 4 and level 2 roadmap data, and the vicinity of
the point of departure and the vicinity of the destination are searched
using the level 2 data and the other area is searched using the level 4
data for route search to reduce the length of time required for the route
search.
In this specification, a level with a large level number is referred to as
a high order level, whereas a level with a small level number is referred
to as a low order level.
FIGS. 21A and 21B illustrate a roadmap depiction of roadmap display data
which are stored in memory as level 4 data and level 3 data. The level 4
roadmap display data and the level 3 roadmap display data are separately
stored in CD ROM media. FIG. 21A shows a roadmap corresponding to one of
the meshes in the level 4 data, i.e., a mesh M4, in which a road D1 and
two roads D2 and D3 that connect at intersections C1 and C2 at the two
ends of the road D1 are present. One of the small areas achieved by
dividing one of the meshes of the level 4 data, i.e., the mesh M4 equally
into sixteen portions, i.e., the hatched small area m3, constitutes a mesh
of the level 3 data, i.e., a mesh M3 and, as shown in FIG. 21B, only a
portion of the road D1, i.e., a road D4 is present in the mesh M3.
There is a problem in the system in the prior art described above in that
when the recommended route is displayed superimposed upon a roadmap at
level 2 or level 1 displayed on the monitor based upon the recommended
route data which constitute the results of a route search performed at
level 4, a great length of time is required for data conversion
processing.
Also, if the detail button is operated while the roadmap corresponding to
the mesh M4 in the level 4 data is displayed on the monitor, the roadmap
corresponding to the mesh M3 in the level 3 data will be displayed on the
monitor. However, since there are no identification data to indicate that
the road D1 and the road D4 are the same road, it is difficult to make a
given road correspond through the different levels. In addition, a similar
problem exists in regard to the route search data, and it is difficult to
make the data searched at level 2 correspond to the data searched at level
4 in recommended route data that are the result of a route search.
Moreover, since there are no identification data to indicate that a road
in the roadmap display data and a road in the route search data are the
same, it is difficult to achieve correspondence of a given road when the
recommended route data are superimposed upon the roadmap display data.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a navigation system with
which the processing time for superimposing a recommended route upon a
display map at a lower order level by using recommended route data at a
higher order level is reduced.
In order to attain this object, a navigation system according to the
present invention comprises: a database apparatus provided with map
display data constituted of data representing road positions and physical
forms provided in separate sets to correspond to different scales and
route search data constituted of data representing connection states of
one road connecting with another road provided in separate sets to
correspond to different scales; and a control apparatus that, when
displaying recommended route data obtained by performing a search using
the route search data at a specific first scale superimposed upon a
roadmap that is displayed on a monitor based upon map display data at a
second scale that is larger than the first scale, reads out physical form
data of the recommended route data obtained by performing the search using
the route search data at the first scale based upon the map display data
at the second scale and displays the physical form data superimposed upon
the roadmap on the monitor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram of an embodiment of a navigation system for
vehicles according to the present invention.
FIG. 2 shows an example of two roads intersecting within a mesh range.
FIG. 3 shows a diagram illustrating link string data.
FIG. 4 shows the structure of roadmap display data.
FIG. 5 shows an example of a roadmap with a plurality of nodes and a
plurality of interpolation points.
FIG. 6 shows a diagram illustrating the link string data corresponding to
the road indicated with the bold line in FIG. 5.
FIG. 7 shows a diagram illustrating offset information that is added into
link string data for reading out immediately preceding data.
FIG. 8 shows a method for reading out the link string data from the rear
end.
FIGS. 9A through 9D show different data lengths of node information and
interpolation point information.
FIGS. 10A and 10B show an example of attribute 1+X coordinate data.
FIGS. 11A and 11B show an example of attribute 2+Y coordinate data.
FIG. 12 shows a diagram illustrating link numbers in route search data.
FIG. 13 shows the structure of route search data.
FIG. 14 shows an overview of the structure in the recommended route data.
FIGS. 15A and 15B show a detailed diagram illustrating the data structure
of the node information and the link information in the recommended route
data.
FIG. 16 shows a flowchart outlining the main processing performed by the
control circuit.
FIG. 17 shows the flowchart continuing from FIG. 16.
FIG. 18 shows a detailed flowchart illustrating the background map drawing
processing performed in step S8 in FIG. 17.
FIG. 19 shows a detailed flowchart illustrating the recommended route
drawing processing performed in step S9 in FIG. 17.
FIGS. 20A through 20C show the procedure taken for drawing a recommended
route in the image memory based upon the recommended route data in this
embodiment.
FIGS. 21A and 21B show a diagram illustrating link strings and links at
different levels.
FIG. 22 shows an example of link data and node data in the prior art.
FIG. 23 shows a diagram illustrating an example of the prior art in which
the separate segments of a road are assigned to separate links across an
intersection.
FIG. 24 shows the relationship between route search data and route display
data in the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a block diagram of an embodiment of a navigation system for
vehicles that is internally provided with a map database apparatus
according to the present invention. In FIG. 1, reference number 1
indicates a current position detection apparatus that detects the current
position of a vehicle, which is constituted with, for instance, an azimuth
sensor that detects the bearing of the vehicle while traveling, a vehicle
speed sensor that detects the speed of the vehicle, a GPS sensor that
detects a GPS signal from a GPS (Global Positioning System) satellite and
the like.
Reference number 2 indicates a control circuit that controls the entire
system and is constituted with a microprocessor and peripheral circuits.
Reference number 3 indicates an input device for inputting destinations
and the like for vehicles, reference number 4 indicates a DRAM that stores
vehicle position information and the like detected by the current position
detection apparatus 1, reference number 5 is an image memory that stores
image data for display on a display device 6 and image data stored in the
image memory 5 are read out as necessary to be displayed on the display
device 6. Reference number 7 indicates an SRAM that stores node
information, link information and the like on the recommended route
calculated by the control circuit 2.
Reference number 8 indicates a map database apparatus that stores various
types of data for performing roadmap display, route search, map matching
and the like, which is constituted with, for instance, a CD ROM device, a
magnetic recording device and the like. In the map database apparatus 8,
map display data that constitute information related to road physical
forms, road classifications and the like, and route search data that
constitute branching point information, intersection information and the
like that are not directly related to road physical forms, are stored. The
map display data are mainly used when displaying a roadmap on the display
device 6 and the route search data are mainly used when calculating a
recommended route.
Next, the data structures of the map display data and the route search data
stored in the map database apparatus 8 are described.
›1! Map Display Data
(1) Overview of Link String Data
Data management of the map display data in this embodiment is performed for
each mesh range representing one of the partitioned areas achieved by
dividing a roadmap into specific ranges, and individual roads present in a
mesh range constitute separate link strings. For instance, as shown in
FIG. 2, when two roads D1 and D2 intersect in one mesh range, the two
roads constitute separate link strings 1 and 2, with the link string 1
comprising links 11 and 12 and the link string 2 comprising links 21-23.
In this example, the links in the link string 1 and the links in the link
string 2 represent roads of the same type. A link is the minimum unit that
can represent a road and, in FIG. 2, the segment between the intersections
constitutes one link unit, with inherent numbers assigned to the
individual links (hereafter referred to as link numbers) for
identification. The intersections in FIG. 2, i.e., the connection points
of the individual links are expressed as nodes N0-N4. Nodes also
constitute the start points and the end points of the individual links
and, as detailed later, interpolation points that further divide the
segments between nodes may sometimes be provided as well.
Also, in this embodiment, when there is a distinct structure such as a
bridge, a tunnel or the like, on a road, the portions of the road
preceding and following the structure constitute separate link strings.
For instance, when there is a bridge and a tunnel on National Highway 246,
as shown in FIG. 3, the portions preceding the bridge and the tunnel, the
blocks corresponding to the bridge and the tunnel and the portions
following the bridge and the tunnel all constitute separate link strings.
In FIG. 3, these strings are designated as link strings 101-105. By making
the portions preceding and following a distinctive structure on a road
separate link strings, search of bridges, tunnels and the like on a
roadmap is facilitated.
The map display data comprise a plurality of sets of data at different
scales. In the explanation of this embodiment, the data at each scale are
referred to as level n (n may be 1-4, for instance) data. Level 1
corresponds to the most detailed roadmap and as the level goes up, a
roadmap over a wider range is presented at a smaller scale. Furthermore,
as detailed later, in this embodiment, identical links at different levels
are managed with identical (inherent) link number to facilitate making
data correspond among different levels. The link number will be explained
later.
(2) Data Structure of Link String Data
To give an explanation of the roads in FIG. 2, the map display data are
structured by providing sets of link string data, each including various
types of information related to the link string 1 or 2-n, for individual
link strings, as shown in FIG. 4, and the data corresponding to each link
string include link string information and node link information, with the
link string information comprising the following types of data, as shown
in FIG. 4.
______________________________________
1 link string size
2 number of element points
3 link attribute
4 road name offset
5 road number
______________________________________
In addition, the node link information comprises the following types of
data, as shown in FIG. 4.
______________________________________
1 attribute 1 + X coordinate
2 attribute 2 + Y coordinate
3 identical node offset
4 guide offset
5 link number
6 altitude information
______________________________________
(3) Link String Information
In FIG. 4, the link string size represents the storage size of the link
string data, by referring to this storage size, prompt access to the next
link string data is achieved. The number of element points data indicate
the total number of node points and interpolation points, the link
attribute data indicate the type of road, such as a national highway, a
prefectural road, an expressway or the like and the road number is the
actual designation number assigned to a national highway or prefectural
road. The explanation of the road name offset is omitted since it is not
relevant to this embodiment. The interpolation points are to be explained
later.
(4) Node Link Information
FIG. 5 shows the link strings 1 and 2 in FIG. 2 in more detail. For
instance, the node link information of the link string 2 indicated with
the bold line in FIG. 5 is as shown in FIG. 6. As shown in the figure, the
data on the link string 2 include node information related to nodes N1,
N02 and N3 (filled circles in FIG. 5) on the link string and interpolation
point information related to the interpolation points (outline circles in
FIG. 5). The node information includes positional X and Y coordinates of
the node, the attribute and the link numbers of links connected to the
node, whereas the interpolation point information includes the positional
X and Y coordinates of the interpolation point. These positional
coordinates are used as physical form data for recommended route display
or physical form data for map matching, to be detailed later. The link
string 2 indicated with the bold line in FIG. 5 includes a link assigned
with a link number 21 located between the nodes N1 and N02, a link
assigned with a link number 22 located between the nodes N02 and N3 and a
link assigned with a link number 23 connected to the node N3. As is
obvious from FIG. 6, the node information on the node N02 is shared by the
link with link number 21 and the link with link number 22. The node
information and the interpolation point information are positioned in the
data structure in the order in which the links are connected. Thus, by
sequentially reading out the link string data starting with the front end
address, the road physical form, the road type and the like of the overall
link string can be detected.
As has been explained, since, in this embodiment, data are managed in units
of link strings within one mesh range and nodes between adjacent links are
shared by the adjacent links, the entire volume of the data can be reduced
compared to the case in which the data are managed in units of links, as
in the example of the prior art shown in FIG. 22. In FIG. 22, links L0-L3
have nodes N0b, N1a, N1b . . . N3a at their start points and end points
and sets of identical node information C01, C10 . . . for indicating
identical nodes are provided as connection information for the individual
nodes.
(5) Offset Indicating an Identical Node
In FIG. 5, of the nodes at the intersection of the link string 1 and the
link string 2 and the link string 3, the node in the link string 1 is
assigned with a reference number N01, the node in the link string 2 is
assigned with a reference number N02 and the node in the link string 3 is
assigned with a reference number N03. In the data structure, the sets of
node information corresponding to the intersecting points N01-N03 each has
a data item referred to as an identical node offset.
The identical node offset is explained in detail in reference to FIG. 7.
For instance, the address value indicating a storage area for the node
information of the node N01 in the link string 1 is stored in memory as
the identical node offset of the node N02 in the link string 2. Likewise,
the address value indicating the storage area for the node information of
the link string 3 is stored in memory as the identical node offset of the
node N01 of the link string 1 and the address value of the address at
which the node information of the node N02 in the link string 2 is stored
in memory as the identical node offset of the node N03 in the link string
3.
Since nodes other than those at intersection, which are indicated as the
intersecting points N01-N03 in FIG. 5, do not intersect other roads, a
specific value, i.e., FFFFh, for instance, that indicates that no other
node exists to constitute an identical node, is stored in the identical
node offset storage areas of the node information for these nodes.
By providing the identical node offset in this manner, even when there are
a plurality of sets of node information in regard to identical nodes, as
in the case of an intersection, the corresponding relationships among the
individual sets of node information can be easily ascertained. Also, in
contrast to an apparatus in the prior art shown in FIG. 23, which requires
5 nodes (N0a-N0d) corresponding to the intersection where three roads
intersect, only three nodes (N01-N03) are required in this embodiment, as
shown in FIG. 5, achieving a reduction in the data volume.
(6) Attribute 1
The attribute 1, which is stored together with the X coordinate of a node
is constituted of offset information for reading out the link string data
in the reverse direction. As explained earlier, in the link string data,
the node information and the interpolation point information and the like
are positioned in the order in which the actual connections are made.
Because of this, by reading out the link string data sequentially from the
front end address in the storage area, the road physical form can be
accurately ascertained starting at the front end position.
There are also situations in which it is necessary to ascertain the road
physical forms from the end by reading out the link string data from the
end. In such a case, after reading out the node information or the
interpolation point information at the rear end, the header position of
the node information or the like that is set immediately before in data
arrangement must be detected. For instance, when reading out the link
string data (FIG. 6) of the link indicated with the bold line in FIG. 5
from the end, it is necessary to first read out the node information on
the node N3 and then to detect the header position of the interpolation
point information that is set immediately before in the data arrangement
to read out the interpolation point information from this header position,
as indicated with the arrows in FIG. 8. However, as explained below, the
data volume of the node information and the interpolation point
information varies among various nodes and interpolation points, and the
header positions of node information and interpolation point information
cannot be determined uniformly.
FIGS. 9A-9D shows varying data volumes of node information and
interpolation point information, with FIG. 9A representing a case in which
node information or the like is constituted with two words, i.e., the X
and Y positional coordinates, FIG. 9B representing a case in which node
information or the like is constituted with three words by adding
identical node offset to the two words in FIG. 9A, FIG. 9C representing a
case in which node information or the like is constituted of four words by
adding guide offset information to the three words in FIG. 9B and FIG. 9D
representing a case in which node information or the like is constituted
of five words by adding a link no. to the four words in FIG. 9C.
As shown in FIGS. 9A-9D, since the data volume of node information or
interpolation point information varies for each case, the information that
indicates the header positions of the node information and the
interpolation point information is added to the link string data in
advance as attribute 1 data in this embodiment. In this embodiment, they
are added together with the X positional coordinates of the individual
nodes and interpolation points.
For instance, FIG. 10A shows an example in which the X positional
coordinates are stored in the lower order 11 bits and information that
indicates the header positions of various sets of node information and the
like is stored in the higher order 2 bits, in the 2-byte data constituting
the attribute 1+X coordinate data. The information that indicates the
number of words that are present up to the header position of each set of
node information or the like is stored in these higher order 2 bits.
Thus, since the information that indicates the header position of the
immediately preceding set of node information or the like is added to the
link string data in this embodiment, even when the link string data are
read out in the reverse direction, the entire node information or the like
can be read out without omissions.
(7) Attribute 2
The attribute 2, which is stored together with the Y coordinate of a node,
includes traffic regulation information, road width information and number
of lanes information. The data length of each set of data of the node link
information that constitutes the link string data is 16 bits (2 bytes=1
word). In the lower order 11 bits of the data indicating the attribute 2+Y
coordinate, the Y positional coordinates are stored and in the higher
order 5 bits, the traffic regulation information, the road width
information and the number of lanes information are stored, as shown in
FIG. 11A. One type of the information from 1-8 in FIG. 11B is selected
through a specific bit combination for the higher order 5 bits.
Since the road width information, the traffic regulation information and
the number of lanes information are stored by using the available bits in
the 2 byte data for storing the positional coordinates or the like of a
node, the road width information, the traffic regulation information and
the like can be added to the link string data without having to increase
the volume of data.
(8) Altitude Information
When displaying a roadmap in three dimensions, data concerning the altitude
differences among a plurality of points on the roadmap are required.
Accordingly, as shown in FIG. 4 in this embodiment, all the altitude
information on the various links constituting a link string is added at
the end of the link string data. It is to be noted that since link string
data including altitude information and link string data without altitude
information are present together, each set of altitude information can be
added to a plurality of nodes and a plurality of interpolation points.
By adding the altitude information to the link string data, a roadmap can
be displayed in three dimensions. In addition, since all the altitude
information is added together at the end of the link string data, the
altitude information can be read out only when it is required and when the
altitude information is not required, such as when displaying a regular
flat map, for instance, only the data immediately preceding the altitude
information need be read out.
(9) Inherent Link Numbers Shared Among Levels
A link number is stored between sets of the attribute 1+X coordinate and
the attribute 2+Y coordinate of node for each link. In this embodiment,
the link number assigned to a link at the highest order level is also
assigned as the link number of corresponding links at lower order levels.
In other words, the link number assigned to a link at the highest order
level is also assigned as the link number of the corresponding links at
the lower order levels as the inherent link number.
Link numbers are explained in further detail in reference to an example
shown in FIG. 12. It is to be noted that, in order to facilitate
understanding, the explanation will be given on the data at levels 6, 4, 2
and 0 among the seven levels, i.e., levels 6-0. When the link string 1 at
the highest order level 6 comprises one link assigned with link number 1,
the link with the link number 1 at the highest order level 6 comprises two
links sharing the identical link number 1 at level 4. The identical link
at the highest order level 6 is constituted of the two links assigned with
the link number 1 constituting the link string 1 and a link with the link
number 1 which constitutes the link string 2 at level 2, whereas the link
string is constituted of a link with the link number 1 constituting the
link string 1, a link with the link number 1 constituting the link string
2 and two links with the link number 1 constituting the link string 3 at
level 0.
By using a link number identical to that used at a higher order level for
the link number of links at lower order levels that correspond to links at
the higher order levels in this manner, the correspondence among identical
link strings at different levels and the correspondence of identical link
strings in the map display data and the route search data are facilitated,
thereby achieving a reduction in processing time.
›2! Route Search Data
The route search data include a plurality of sets of data corresponding to
a plurality of sets of roadmap display data for different scales, and the
data for each scale are referred to as level m (m, may be, for instance,
2, 4) data. In addition, as explained before in this embodiment, identical
links at different levels are managed through identical link number to
facilitate correspondence of data at different levels and the
correspondence with the roadmap display data.
FIG. 13 shows the data structure of route search data. As shown in the
figure, in the route search data, node information that indicates the
connecting relationship with other nodes is stored for each connecting
point (node) of links, which are the minimum units for expressing a road
physical form. Each set of node information is constituted with home node
information and adjacent node information, with the node positional
coordinates stored in the home node information. In the adjacent node
information, as shown in the figure, the adjacent node no., the link no.
from the home node to the adjacent node, the link cost of the link and
traffic regulation information on that link are stored. Also, various sets
of node information are stored in the order of link connections and the
node no. of the home node can be ascertained by the order in which it is
stored. Because of this, even without storing the node nos. of the home
nodes as home node information, the node nos. of the home nodes can be
ascertained, achieving a reduction in memory requirement.
›3! Recommended Route Data
FIG. 14 shows an outline of the data structure of recommended route data
which represent a recommended route from a point of departure to a
destination which has been searched based upon the route search data. In
the recommended route data, node information and link information on the
recommended route are stored, while classified in units of mesh ranges. It
is to be noted that a mesh range refers to a partitioned range when a
roadmap is partitioned into units of specific ranges.
As shown in FIG. 14, the recommended route data are constituted with a mesh
code, the number of nodes, node information, the number of link
classifications, link information, ferry information and tunnel
information The number for identifying the mesh range is stored in the
storage area for the mesh code, the number of nodes present within a mesh
range is stored in the storage area for the number of nodes and, as shown
in detail in FIG. 15A, the node no., the positional coordinates, the
distance cost and the like of each node within a mesh range are stored in
the storage area for the node information. In addition, the number of link
classifications that are present inside a mesh range is stored in the
storage area for the number of link classifications and, as shown in
detail in FIG. 15B, the link classification, the number of links, the link
no. and the like of each link within a mesh range are stored in the
storage area for the link information. FIGS. 15A and 15B illustrate a case
in which there are two link strings 1 and 2 within the area indicated by
the same mesh code.
It is to be noted that, as explained above, recommended route data are
prepared at different levels and, in this embodiment, recommended route
data at level 2 are prepared for the vicinities of the start point and the
end point on the recommended route while recommended route data at level 4
are prepared for the middle range between the start point and the end
point.
The following is an explanation of the operation performed in this
embodiment in reference to the flowchart, and in this embodiment, the
recommended route is displayed on the display device 6 in the following
manner. The recommended route is searched by using the route search data
at level 4 and level 2 to create recommended route data at level 4 and
level 2, and then, the recommended route data at level 4 is converted into
recommended route data at level 2, and then based upon the recommended
route data at level 2 and the roadmap display data at level 2 and level 1,
the recommended route is drawn and superimposed upon the roadmap at level
2 or level 1, which is displayed on the display device 6, with the
recommended route highlighted with a red bold line, for instance.
FIGS. 16 and 17 are a flow chart illustrating the outline of the main
processing performed by the control circuit 2. In step S1 in FIG. 16, the
vehicle position is detected by the current position detection apparatus
1. In step S2, the destination, which has been input via the input device
3, is read in. In step S3, based upon the map display data stored in the
map database apparatus 8, the start point and the end point of the route
search are set on roads for which route search is possible. For instance,
the start point of a vehicle may be the current position of the vehicle
(vehicle position) and the end point is the destination.
In step S4, using route search data at level 2, route search in the
vicinity of the start point of the route search is performed, and a
plurality of candidates for the recommended route in the vicinity of the
start point are selected. In step S5, using route search data at level 2,
route search in the vicinity of the end point of the route search is
performed, and a plurality of candidates for the recommended route in the
vicinity of the end point are selected.
In step S6, using route search data at level 4, route search is performed
for routes between the candidates for the recommended routes selected in
step S4 and step S5, and a recommended route from the start point to the
end point is calculated.
Route search data at different levels are used for the vicinities of the
start point and the end point, and the middle range between the start
point and the end point in this manner because if route search is
performed using route search data at level 2 for the entire route, the
data quantity will be very large and, as a result, the calculation time
required in route search will increase. In step S7, the information
related to the recommended route calculated in step S6 is stored in the
SRAM 7 as recommended route data.
When the processing performed in step S7 in FIG. 16 is completed, the
operation proceeds to step S8 shown in FIG. 17, in which the background
map drawing processing, the details of which are shown in FIG. 18, is
performed to draw (store) data related to the roadmap in the vicinity of
the recommended route in the image memory 5 for display on the display
device 6. First, in step S11 in FIG. 18, map display data corresponding to
the vicinity of the current vehicle position are read from the map
database apparatus 8. Next, in step S12, a portion of the map display data
thus read, is drawn (stored) in the image memory 5.
When the processing performed in step S12 in FIG. 18 is completed, the
operation proceeds to step S9, shown in FIG. 17, in which the data
required to display the recommended route calculated in step S3 are also
drawn over (stored) in the image memory 5. The recommended route drawing
processing performed in step S9 is described in more detail later. In step
S10, the data stored in the image memory 5 are read out and the
recommended route and the roadmap in the vicinity are displayed on the
display device 6.
FIG. 19 is a detailed flowchart illustrating the recommended route drawing
processing performed in step S9 in FIG. 17. In step S51 in FIG. 19, the
display range for the recommended route is set in correspondence to the
roadmap range displayed on the display device 6. In step S52, a decision
is made as to whether or not the display range for the recommended route
is included within the range over which the route search has been
performed using the route search data at level 4. If a negative decision
is made, the operation proceeds to step S54, whereas if an affirmative
decision is made in step S52 in FIG. 19, the operation proceeds to step
S53 to convert the recommended route data at level 4 stored in the SRAM 7
to recommended route data at level 2. This conversion processing is to be
detailed later.
Step S54 follows step S52 or step S53 in FIG. 19, and a decision is made as
to whether the display scale of the roadmap is set at (1/10,000 or
1/20,000) or (1/40,000 or 1/80,000). If the setting is at (1/10,000 or
1/20,000), the operation proceeds to step S55, in which the recommended
route is drawn over (superimposed) in the image memory 5, based upon the
recommended route data at level 2 and, the road type and link numbers of
the map display data at level 1.
If, on the other hand, a decision is made in step S54 that the scale is set
at (1/40,000 or 1/80,000), the operation proceeds to step S56, in which
the recommended route is drawn over in the image memory 5 based upon the
recommended route data at level 2, and the road type and link numbers of
the map display data at level 2.
As shown in FIGS. 13 and 14, the route search data and the recommended
route data in this embodiment hold only the connection information on link
connections and do not hold information in regard to road physical form.
Consequently, in order to draw a recommended route superimposed upon the
roadmap on the monitor, it is necessary to extract the physical form data
from the roadmap data based upon the recommended route data. FIGS. 20A-20C
illustrate the procedure that is followed in order to display the
recommended route on the monitor based upon the recommended route data.
FIG. 20A shows recommended route data at level 4 in which the link 1
constituting the link string 1 is present between the front end node N0
and the rear end node N1. FIG. 20B illustrates the recommended route data
at level 2 and recommended route display data at level 2 for drawing the
physical form data which are extracted from the roadmap display data at
level 2 based upon the recommended route data at level 2, superimposed in
the image memory 5. In FIG. 20B the link string 1 of the recommended route
data at level 2 comprises the link 1 located between the nodes N0 and Na
and the link 1 located between the nodes Na and N1. FIG. 20C illustrates
the recommended route display data at level 1 for drawing the physical
form data which are extracted from the roadmap display data at level 1
based upon the recommended route data at level 2, superimposed in the
image memory 5.
When the operation proceeds from step S54 to step S56 in FIG. 19, i.e.,
when drawing the recommended route on the roadmap at level 2 based upon
the recommended route data at level 2, the coordinate values of the node
N0, the interpolation point Hb, the node Na, the interpolation point Hc
and the node N1 constituting the link string 1, as shown in FIG. 20B, are
read out by referencing the roadmap display data at level 2, with common
link number 1, the start node N0 and the end node N1 of the link string 1
used as pointers. It is desirable to search the map display data within
identical mesh code as the mesh code of the recommended route data in
order to reduce processing time. Then, the link string comprising two
links with the link number 1 in the recommended route data is drawn on the
road map at level 2 which is drawn in the image memory 5.
When the operation proceeds from step S54 to step S56 in FIG. 19, i.e.,
when drawing the recommended route on the roadmap at level 1 based upon
the recommended route data at level 2, the coordinate values of the node
N0, the interpolation point Hd, the interpolation point He, the node Nb,
the interpolation point Hf and the node Nc constituting the link string 1
and the coordinate values of the node Nc, the interpolation point Hg, the
interpolation point Hh, the interpolation point Hi and the node N1
constituting the link string 2, as shown in FIG. 20C, are read out by
referencing the roadmap display data at level 1, with common link number 1
of the two links, the start node N0 and the end node N1 of the link string
1 used as pointers. As explained before, it is desirable that mesh code at
level 1 is obtained based upon mesh code of the recommended route data at
level 2, then the map display data is searched within identical mesh code
as the mesh code of the recommended route data in order to reduce
processing time. Then, the link string comprising two links of link 1 in
the recommended route data is drawn on the roadmap at level 1 drawn in the
image memory 5.
It is to be noted that the processing through which the recommended route
data at level 4 are converted to recommended route data at level 2
performed in step S53 | | |
