JPH0954545A - Map display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a map display device capable of converting plane map data to bird's-eye view map data with simple arithmetic operation. SOLUTION: An on-vehicle navigation device has a reader 2b which reads the plane map data from a CD-ROM 2a storing the plane map data of road maps and a present position detector 1 which detects the present position of the vehicle. The position coordinates of the nodes included in the plane road maps are converted to the position coordinates of the nodes on the bird's-eye view maps by utilizing a conversion table. In such a case, the position coordinates described above are converted to the position coordinates of the nodes on the bird's-eye view maps looked down in a prescribed direction at a prescribed looking down angle and prescribed double spread angle from the view point set in the sky around the detected present position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a map display apparatus for converting a two-dimensionally displayed map into a bird's-eye view map by a bird's-eye view method for display.

[0002]

2. Description of the Related Art When a road map is displayed on a display device, there is a vehicle-mounted map display device that displays the road map around the current location of the vehicle by enlarging it from a distance, that is, a so-called bird's-eye view method. It is known (for example, Japanese Patent Laid-Open No. 2-244188). The device disclosed in the above publication is
A viewpoint is placed above the current position of the vehicle, and a state of looking down the traveling direction of the vehicle from this viewpoint is displayed on the screen of the display device. When such a bird's-eye view display is performed, the road map around the current position can be enlarged and displayed, and a wide range from the current position to the distant place can be displayed, so that the connection status of the road map can be easily visually recognized. In addition, it is possible to display a realistic road map as if the driver were looking down at the road map.

[0003]

In order to display a road map according to the bird's-eye view method (hereinafter, referred to as a bird's-eye view map), it may be possible to store the road map for displaying the bird's-eye map in a CD-ROM or the like in advance. However, since the map scale of the bird's-eye view map changes continuously as the viewpoint moves, the data amount of the road map becomes enormous. For this reason, it is general to convert road map data for normal plane map display into bird's-eye view map data for display. However, since the conversion calculation to the bird's-eye view map data must be performed every time the viewpoint position moves, it takes time to rewrite the screen and the usability may be deteriorated.

An object of the present invention is to provide a map display device capable of converting planar map data into bird's-eye view map data by a simple calculation.

[0005]

[Means for Solving the Problems]

(1) The map display device according to the present invention uses a conversion table without performing complicated arithmetic operations when converting planar map data into bird's-eye view map data for displaying as a bird's-eye view map according to the bird's-eye view method. The data for displaying the bird's-eye view map is created from the data. (2) The conversion table performs data conversion so that the bird's-eye view map is displayed on the monitor when the plane map is looked down from a viewpoint placed in the sky around a predetermined position on the map at a predetermined look-down angle and spread angle. To do. (3) When the present invention is applied to the road map display device, the conversion table converts the position coordinates of the node for representing the road map into the position coordinates of the corresponding node on the bird's-eye view map by the bird's-eye view method. In this case, data conversion is performed so that the bird's-eye view map, which is displayed by looking down at the road map at a predetermined look-down angle and spread angle from the viewpoint placed above the current position of the vehicle on the road map, is displayed on the monitor. To do. (4) When a virtual rectangular display screen that is orthogonal to the looking down line is set at a position that is a predetermined distance away from the viewpoint on the looking down line that extends toward the plane of the road map at a predetermined looking down angle through the viewpoint. Bird's-eye view map display data is created so that a road map of a trapezoidal area on the road map is projected on a virtual rectangular display screen to display a bird's-eye view map. (5) When the display screen is divided into at least two areas, a first area near the current position of the vehicle and a second area away from the current position of the vehicle, the conversion table has a first area and a second area. And a first table and a second table, respectively, suitable for (6) When an area for coordinate conversion of the road map data to be displayed is selected, if there is a node that is out of the area among the polygon or link nodes at least part of which is included in the area data, Data conversion is performed by correcting the position coordinates of the protruding node to a predetermined position within the selected range. (7) When the present invention is applied to a vehicle-mounted navigation device, the navigation device includes a reading device that reads planar map data from a storage medium that stores planar map data of a road map, and a current position that detects the current position of the vehicle. The detection device and the position coordinates of the nodes included in the road map around the detected current position, from the viewpoint set in the sky around the detected current position, in a predetermined direction, a predetermined look-down angle, and a predetermined spread angle. With the memory circuit that stores the function table that converts to the position coordinates of the node on the bird's-eye view map, the conversion table is operated according to the coordinate position of the node on the road map, and the data on the coordinate position of the node on the bird's-eye map is operated. Read out and create bird's-eye view map display data for displaying the bird's-eye view map on the monitor based on the read-out data. It includes a bird's-eye-view map display data generating circuit.

[0006]

1 is a block diagram of an embodiment of a vehicle-mounted map display device according to the present invention. In FIG. 1, reference numeral 1 denotes a current position detection device that detects the current position of the vehicle, such as a direction sensor that detects the traveling direction of the vehicle, a vehicle speed sensor that detects the vehicle speed, and a GPS (Global Positioning System).
stem) A GPS sensor or the like for detecting GPS signals from satellites. Reference numeral 2a is a map recording medium for storing road map data of a plurality of different map scales. The map recording medium 2a is removably connected to the reading control device 2b, and the reading control device 2b responds to an instruction from a CPU (to be described later).
The road map data stored in is read. The reading device 2b is, for example, a CD-ROM device.

Reference numeral 3 is a control circuit for controlling the entire apparatus,
It consists of a microprocessor and its peripheral circuits. Reference numeral 4 denotes an input device for inputting a destination of the vehicle and the like, 5 denotes a display memory for storing image data to be displayed on the display device 6, and the image data stored in the display memory 5 is read out as appropriate to the display device. 6 is displayed. A ROM 7 stores a function table for coordinate conversion, which will be described later.

<Description of Main Processing> FIG. 2 is a flowchart showing the main processing of the control circuit 3, and the operation of one embodiment will be described below based on this flowchart.
It should be noted that when the main power source is turned on, the control circuit 3 is set to
Start the process.

In step S1 of FIG. 2, a recommended route and a destination are set. The destination is set by the operator via the input device 4, and the recommended route is automatically set by calculation using, for example, the well-known Dijkstra method. Alternatively, the recommended route candidates may be stored in advance in the ROM 7 or the like, and any one of them may be selected as the recommended route. Note that the recommended route may not be set if there is no particular need.

In step S2, the current position of the vehicle is detected by using the current position detection device 1. In step S3, as shown in FIG.
The bird's-eye view map display processing showing the details is performed. Details of this bird's-eye view map display processing will be described later.

In step S4, the current position of the vehicle is detected as in step S2. In step S5, it is determined whether the road map on the screen is updated, that is, whether the road map is rewritten. Here, it is determined that the road map is updated, for example, when the vehicle travels for a predetermined distance or more, or when the operator instructs scrolling through the input device 4.

If the determination in step S5 is affirmative, the process returns to step S3 to rewrite the screen, and if the determination is negative, the process proceeds to step S6. In step S6, it is determined whether to continue the main process of FIG. For example, if a power switch (not shown) is turned off or a switch for stopping the process is operated, the determination in step S6 is denied and the main process of FIG. 3 is ended.

If the determination in step S6 is affirmative, the process proceeds to step S7, the display of the attached information is updated, and then the process returns to step S4. Here, the attached information refers to, for example, a vehicle position mark or the like displayed at the current position of the vehicle, and in step S7, the display position of the attached information such as the vehicle position mark or the like is changed according to the traveling distance of the vehicle.

<< Description of Bird's-Eye Map Display Processing >> FIG. 3 is a detailed flowchart of the bird's-eye map display processing in step S3 of FIG. In step S51 of the figure, the detailed map data and the wide area map data stored in the map recording medium 2a are read. In step S52, the read road map data is converted into real length data. In step S53, XY
Conversion processing into two-dimensional coordinates of two axes is performed. Step S54
Then, the Y-axis coordinate is converted into a coordinate that can refer to a function table described later. In step S55, detailed data coordinate conversion processing detailed in FIG. 4 and wide area data coordinate conversion processing detailed in FIG. 5 are performed. Details of the processing of FIGS. 4 and 5 will be described later.

In step S56, of the data included in the bird's-eye view map data obtained by the detailed data coordinate conversion processing of FIG. 4 and the bird's-eye view map data obtained by the wide area data coordinate conversion processing of FIG. The data to be displayed is clipped, and the clipped data is drawn in the display memory 5 in step S57. As a result, a bird's-eye view map using the detailed map data is displayed from the lower side of the screen to a predetermined height, and a bird's-eye view map using the wide area map data is displayed above the part. The reason why the type of road map data is changed according to the height position of the screen is that the lower side of the screen is displayed at a larger scale in the case of the bird's-eye view map display.

FIG. 4 is a detailed flowchart of the detailed data coordinate conversion process of step S55 of FIG. In step S101 of FIG. 4, an area for converting the plan map data into the bird's-eye view map data is set based on the vehicle position detected in step S2 of FIG. This area is represented by a rectangular area RC extending in the vehicle traveling direction as shown in FIG. Hereinafter, the area RC will be referred to as a coordinate conversion area. The trapezoidal region RC1 inside the coordinate conversion region indicates the range actually displayed on the display device 6.

In step S102, the polygons or links which are not selected yet are selected from the polygons or links at least partially included in the coordinate conversion area. A polygon represents a closed area such as a lake, a park, or a green space, and has a plurality of nodes. A link is each section when a road is divided into a plurality of sections, and nodes are set at the start and end of the link, and each node has position coordinates. In step S103, the position coordinate E (Ex, Ey) of the node which has not been subjected to coordinate conversion is selected from the nodes belonging to the selected polygon or link. In step S104, it is determined whether the selected node is outside the coordinate conversion area. That is, in this step S104, if a part of the polygon or link selected in step S102 is out of the coordinate conversion area, it is determined whether or not the node in the protruding part is selected in step S103.

If the determination in step S104 is affirmative, the process proceeds to step S105, and the node position is corrected on one side of the coordinate conversion area closest to the selected node position. Details of the processing in step S105 will be described later.

In step S106, the node position coordinate E is calculated using the function tables fb (Ey) and gb (Ey) described later.
(Ex, Ey) is converted into bird's-eye view map display coordinates S (Sx, Sy). Details of the process of step S106 will be described later.

When the process of step S106 is completed, the process proceeds to step S107, and it is determined whether or not coordinate conversion has been performed for all nodes belonging to the selected polygon or link. If the determination is negative, the process returns to step S103,
If the determination is positive, the process proceeds to step S108. In step S108, it is determined whether or not there is a polygon or link that has not been converted in the coordinate conversion area. If the determination is affirmative, the process returns to step S102, and if the determination is negative, the process returns.

On the other hand, FIG. 5 is a detailed flowchart of the wide area data coordinate conversion processing in step S55 of FIG. The wide area data coordinate conversion process is common to the detailed data coordinate conversion process except that the function table used for the coordinate conversion is different. That is, in step S206 of FIG. 5, the node position coordinates E are calculated using function tables fa (Ey) and ga (Ey), which will be described later.
(Ex, Ey) is converted into bird's-eye view map display coordinates S (Sx, Sy).

As described above, in the bird's-eye view map display processing of FIGS. 3 to 5, a coordinate conversion area spreading in the vehicle traveling direction is set around the vehicle position on the road map, and polygons and links existing inside the area are set. Select sequentially. Next, the nodes belonging to the selected polygon and link are selected one by one, and the position coordinates of each node are converted into bird's-eye view map display coordinates. More specifically, both the detailed map data and the wide area map data are converted into bird's-eye view map data, and after the conversion is completed, each data is clipped and drawn in the display memory 5.

<< Explanation of coordinate conversion using detailed map data >> FIG. 7 is a diagram for explaining conversion into bird's-eye view map data.
An example is shown in which the road map is the XY plane, the viewpoint M is placed on the Z axis that is orthogonal to the XY plane, and the downward angle from the viewpoint M is θ. As shown in the enlarged view of FIG. 8A, the illustrated rectangle abcd indicates a virtual display range of the display device 6, and the trapezoid ABCD of FIG. 7 indicates the road map range displayed on the display device 6. That is, the bird's-eye view map is created by projecting the road map in the trapezoid ABCD onto the virtual display screen abcd.

In order to convert the road map data into the bird's-eye view map data, first, from the height Vz of the viewpoint M and the viewpoint M so that all the road map data in the trapezoidal area ABCD shown in the figure can be displayed on the display device 6. After determining the down-looking angle θ and the spread angle φ from the viewpoint, the coordinates in the trapezoidal area ABCD are used to determine the coordinates in the display screen area abcd.
Convert to coordinates inside. This area abcd is called a virtual display screen DSP. When a line segment passing through the viewpoint M and looking down at the angle θ is LN, the line segment L
A virtual display screen DSP spreads in a plane orthogonal to the line segment LN at a point separated from the viewpoint M on N by a distance Ds. At this time, the looking-down angle θ is set such that the vicinity of the center line connecting the midpoints of the upper side and the lower side of the display screen of the display device 6 is the destination direction.

FIG. 9 is a view obtained by projecting FIG. 7 on the YZ plane. In FIG. 9, the viewpoint position is M, and the virtual display screen DSP
Is O ', the coordinate position on the road map (coordinate origin) corresponding to the center O'of the display screen area is O, the current position of the vehicle is G, and the arbitrary coordinate position on the road map is E (Ex, Ey ). The point where the line segment LN intersects the plane is the display screen D
A point that is the center O ′ of SP and the line segment LN intersects the XY plane is a coordinate origin O on the road map. Further, the intersection of the line perpendicular to the line MO from the point E is Q, and the intersection of the line ME and the virtual display screen DSP is R. At this time, the relationship of Expression (1) is established.

## EQU00001 ## MQ = MO + OQ = K + Ey.cos .theta. (1) In the equation (1), the length of the line segment MO is K, and the angle formed by the line segments OE and OQ is .theta ..

In FIG. 9, the triangle MO'R and the triangle M
Since it has a similar relationship with QE, the equation (2) holds.

## EQU2 ## MQ: MO '= EQ: RO' (2)

Here, the number of dots in the horizontal direction of the display screen area of the display device 6 is 360 and the number of dots in the vertical direction is 240, and the coordinate origin (0, 0) of the virtual display screen DSP is shown in FIG.
When the lower left corner is shown as shown in (b), the coordinates of the center O ′ of the virtual display screen DSP are represented by (180, 120). Therefore, when the coordinate position of the arbitrary point AP on the virtual display screen DSP is represented by (Sx, Sy), the equation (2) is represented as the equation (3).

## EQU00003 ## (K + Ey.cos .theta.): Ds = Ey.sin .theta. :( Sy-120) (3) When formula (3) is modified, formula (4) is obtained.

## EQU00004 ## Sy = {(Ds.times.Ey.sin .theta.) / (K + Ey.cos .theta.)} + 120 (4)

On the other hand, FIG. 10 is a diagram in which FIG. 7 is projected on the XY plane. In FIG. 10, a triangle MO′V and a triangle M
Since it has a similarity relationship with EW, and its similarity ratio is the same as the ratio in equation (3), the relationship in equation (5) holds.

## EQU00005 ## (K + Ey.cos .theta.): Ds = Ex: (Sx-180) (5) When equation (5) is modified, it becomes equation (6).

[Equation 6] Sx = {Ex · Ds / (K + Ey · cos θ)} + 180 (6)

In this way, the node coordinates (E
By substituting (x, Ey) into the expressions (4) and (6), the coordinates can be converted into the coordinates (Sx, Sy) for displaying the bird's-eye view map.

<< Explanation of coordinate conversion using wide area map data >> Regardless of whether the detailed map data or the wide area map data is used for conversion, basically (4), (6)
The conversion to the bird's-eye view map display coordinates is performed by the same formula as the formula, but the coefficients of the formulas (4) and (6) are partially different depending on the type of map data.

11 and 12 are diagrams showing an example in which the Y-axis coordinate Ey of the road map data exceeds a predetermined value V. The predetermined value V is the boundary position between the area to be converted using the detailed map data and the area to be converted using the wide area map data. As shown in the figure, if the fact that the triangle MO′R and the triangle MQE ′ are similar to each other is used, the relationship of the above-mentioned expression (2) is established.

Here, the intersection of the perpendicular line drawn from the coordinate V to the line segment MQ is R ′, P = V · sin θ, the length of the line segment MR ′ is K2, and the coordinate of the E ′ point with reference to the V point. (Ex2,
Ey2), the equation (2) is expressed as the equation (7).

[Equation 7] Ds: (K2 + Ey2 · cos θ) = (Sy−120) :( P + Ey2 · sin θ) = (Sx−180): Ex2 (7) ) Is obtained.

## EQU00008 ## Sx = Ex.Ds / (K + Ey.cos .theta.) + 180 (8)

[Equation 9] Sy = Ds × (P + Ey2 · sin θ) / (K2 + Ey2 · cos θ) +120 (9)

Thus, (4), (6), (8),
According to the expression (9), the detailed map data or the wide area map data can be converted into the bird's-eye view map data, but since each expression includes division, the calculation takes time. Therefore, in one embodiment, when the coordinate conversion is performed using the detailed map data, the function table f as shown in equations (10) and (11) is used.
b (Ey) and gb (Ey) are created in advance and stored in the ROM.

Fb (Ey) = Sy = (Ds × Ey · sin θ) / (K + Ey · cos θ) +120 (10)

Gb (Ey) = Ds / (K + Ey · cos θ) (11)

Similarly, when coordinate conversion is performed using wide area map data, function tables fa (Ey) and ga (Ey) as shown in equations (12) and (13) are created in advance.

(12) fa (Ey) = Sy = Ds × (P + Ey · sin θ) / (K2 + Ey · cos θ) +120 (12)

[Equation 13] ga (Ey) = Ds / (K2 + Ey · cos θ) (13)

By storing such a function table in the ROM 7 in advance, it is possible to perform conversion into the coordinates (Sx, Sy) for displaying the bird's-eye view map without performing complicated calculations. That is, for the Y-axis coordinate, the function table fb
The output of (Ey) and fa (Ey) becomes the bird's-eye view map display coordinates Sy as they are, and the function table gb for the X-axis coordinates.
The bird's-eye view map display coordinates Sx are obtained by substituting the values obtained by (Ey) and ga (Ey) into the equation (14) for calculation.

(14) Sx = g (Ey) · Ex + 180 (14)

Since the possible values of Sx and Sy are limited by the number of display dots on the screen, it is meaningless to increase the data amount of the table too much. Therefore, for example, when the number of display dots on the screen is 360 dots in the X-axis direction and 240 dots in the Y-axis direction, 0 ≦ Sx ≦ 360, 0
Only values in the range such that ≤Sy≤240 need to be stored in the table.

FIG. 13A is an example of a data layout diagram of the detailed map function tables fb (Ey) and gb (Ey) stored in the ROM. As shown in FIG. 13A, Y
For each axis coordinate value, a corresponding table value gb, fb is arranged as a set and a total of 1024 sets (2048 sets) are arranged. Further, the coordinates (two-point coordinates in FIG. 6) of the coordinate conversion area set in step S101 in FIG. 4 are stored in the head portion of the table.

Similarly, FIG. 13B is an example of a data layout diagram of the function tables fa (Ey) and ga (Ey) for the wide area map. As shown in the figure, for each Y-axis coordinate value, the corresponding table values ga and fa form a set of 512 sets (102 sets).
4 pieces) are arranged.

<< Description of Correction of Node Position >> In step S105 of FIG. 4, when some nodes belonging to the selected polygon or link are outside the coordinate conversion area, the coordinate positions of these nodes are set to one side of the coordinate conversion area. The process of moving it up is being performed.

FIG. 6 is a diagram showing an example in which a part of the polygon is outside the coordinate conversion area. In the case of FIG. 6, a node outside the coordinate conversion area is moved to one side of the coordinate conversion area closest to each node position as shown in the figure. Specifically, as illustrated, the nodes N1 and N2 are moved to the closest positions n1 and n2 on the side L1. Similarly, node N3
Is moved to the closest position n3 on the side L2. On the other hand, the node n4 is moved to the corner position n4 of the coordinate conversion area.

By correcting the node position in this way,
The polygon or the link does not straddle a plurality of coordinate conversion regions, and the coordinate conversion process to the bird's-eye view map display coordinates can be simplified.

On the other hand, when the node position is corrected as shown in FIG. 6, there is a drawback that the shape of the polygon or the link is changed as shown by the hatched portion in the figure. However, if at least one node is arranged between the trapezoidal area that is actually displayed on the screen and the outer edge of the coordinate transformation area around it, the polygons and There is no risk of the link shape changing.

In the above-mentioned one embodiment, the example in which the function table is provided for each of the two types of road map data has been described. However, for example, a function table is provided for each viewpoint position and the looking-down angle so that the function tables can be continuously switched. By doing so, it becomes possible to look around 360 degrees around the viewpoint position.

A CD-R connected to the computer
It is also possible to set a storage medium in a reading device such as an OM and achieve the same function as that of the map display device or the vehicle-mounted navigation device as described above. In that case, the computer is connected to a storage device that stores the plan map data of the road map and a current position detection device that detects the current position of the vehicle, and the procedure for reading the plan map data from the storage device in the storage medium. And a procedure for reading the current position from the current position detection device, and the position coordinates of the nodes included in the road map around the detected current position, from the viewpoint set in the sky around the detected current position, Direction, a predetermined look-down angle, and a bird's-eye view by operating the conversion table according to the coordinate position of the node on the road map when converting the position coordinates of the node on the bird's-eye view map when looking down at a predetermined angle A bird's-eye view map table for reading the data regarding the coordinate position of the node on the map and displaying the bird's-eye view map on the monitor based on the read data. For storing a program for executing the steps to create the data.

In the embodiment configured as described above, the flow chart of FIG. 3 is used for the bird's-eye view map display data generation circuit, the ROM 7 is used for the table storage circuit, and step S101 of FIG. 4 and step S201 of FIG. In the map data selection circuit, step S102 of FIG. 4 and step S of FIG.
202 is a figure selection circuit, step S104 of FIG. 4 and step S204 of FIG. 5 are out-of-range node extraction circuits, and FIG.
Step S105 of FIG. 5 and step S205 of FIG. 5 correspond to the node position correction circuit, respectively.

[0046]

【The invention's effect】

(1) As described in detail above, according to the present invention, the conversion map is used to convert the plan map data into the bird's-eye view map data, so that it is not necessary to perform a complicated arithmetic operation and the processing time is reduced. Is shortened. (2) In addition, for example, the scale factor of the first region near the current position of the vehicle on the display screen is set to the second scale distance from the current position of the vehicle.
If the scale ratio is larger than that of the area, the first and second tables suitable for each area can be provided, and the processing time can be further shortened. Also, if a function table is provided for each viewpoint position and angle of looking down and the function tables are switched continuously, it becomes possible to look around the 360 ° direction around the viewpoint position. (3) Coordinate conversion of map data to be displayed When you select the area to be selected, among the polygon or link nodes that include at least part of the data in that area,
If there is a node protruding from the area, only the map data within the predetermined range is corrected by correcting the position coordinates of the protruding node to a predetermined position within the selected range and performing data conversion. The bird's-eye view map can be displayed by converting it to the bird's-eye view map data, and the conversion process is simplified, and the bird's-eye view map is displayed comfortably even if there is data that crosses the bird's-eye view map creation area and the area that does not.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a vehicle-mounted map display device according to the present invention.

FIG. 2 is a flowchart showing main processing performed by a control circuit.

3 is a detailed flowchart of a bird's-eye view map display process in step S3 of FIG.

FIG. 4 is a detailed flowchart of detailed data coordinate conversion processing in step S55 of FIG.

5 is a detailed flowchart of wide area data coordinate conversion processing in step S55 of FIG.

FIG. 6 is a diagram showing a coordinate conversion area.

FIG. 7 is a diagram illustrating conversion into bird's-eye view map data.

8A is an enlarged view of the rectangular abcd area in FIG. 7, and FIG. 8B is a diagram illustrating coordinates of the rectangular abcd area.

FIG. 9 is a diagram obtained by projecting FIG. 7 on a YZ plane.

FIG. 10 is a diagram obtained by projecting FIG. 7 on an XY plane.

FIG. 11 is a diagram showing an example in which the Y-axis coordinate Ey of the road map data exceeds a predetermined value V and FIG. 7 is projected on the YZ plane.

FIG. 12 is a diagram showing an example in which the Y-axis coordinate Ey of the road map data exceeds a predetermined value V and FIG. 7 is projected on the XY plane.

FIG. 13 is a data layout diagram of a function table stored in a ROM.

[Explanation of symbols]

 1 present position detection device 2a map recording medium 2b read control device

Claims (13)

[Claims] 1. A table storage circuit for storing a conversion table for converting data for displaying a map as a two-dimensional map into data for displaying the map as a bird's-eye view map by a bird's-eye view method, and the conversion table from the conversion table. A map display device comprising: a bird's-eye view map display data creation circuit that creates bird's-eye view map display data for displaying the bird's-eye view map on a monitor based on the data. 2. The map display device according to claim 1, wherein the conversion table is a bird's-eye view map when the planar map is looked down from a viewpoint placed in the sky around a predetermined position on the map at a predetermined look-down angle and spread angle. Data conversion so that is displayed on the monitor. 3. The map display device according to claim 2, wherein the conversion table is a function table for converting the position coordinates of the node on the planar map into the position coordinates of the node on the bird's-eye view map. 4. The map display device according to claim 2, wherein the bird's-eye view map display data creation circuit is located at a predetermined distance from the viewpoint on a down-looking line extending through the viewpoint at the down-looking angle toward the plane of the map. When a virtual rectangular display screen orthogonal to the looking down line is set at a distant position, a map of a trapezoidal area on the map plane is projected on the virtual rectangular display screen to display a bird's-eye view map. Create such bird's-eye view map display data. 5. A table storage circuit for storing a function table for converting position coordinates of a node for representing a road map into position coordinates of the node on a bird's-eye view map displayed by a bird's-eye view method, and the function table. A map display device comprising: a bird's-eye view map display data creation circuit that creates bird's-eye view map display data for displaying the bird's-eye view map based on the converted data. 6. The map display device according to claim 5, wherein the function table is obtained by looking down at the road map at a predetermined look-down angle and spread angle from a viewpoint placed above the current position of the vehicle on the road map. Data conversion is performed so that the bird's-eye view map is displayed on the monitor. 7. The map display device according to claim 6, wherein the bird's-eye view map display data creating circuit is a predetermined line from the viewpoint, which is on a down line extending through the viewpoint at the down angle toward the plane of the road map. At a distance,
A bird's-eye view map for displaying a bird's-eye view map by projecting a road map of a trapezoidal area on the road map onto the virtual rectangle display screen when setting a virtual rectangle display screen orthogonal to the looking-down line. Create display data. 8. The map display device according to claim 7, wherein a center position on the virtual display screen is O ′, a reference position on the road map corresponding to the center position O ′ is O, and the virtual position from the viewpoint. A distance to a typical display screen, a distance from the viewpoint to the reference position O, K, an X-axis coordinate of a node to be converted on a road map, an Y-axis coordinate of the node, Ey, the node When the X-axis coordinate on the display screen corresponding to the X-axis coordinate Ex of Sx is Sx and the Y-axis coordinate on the display screen corresponding to the Y-axis coordinate Ey of the node is Sy, the table storage circuit is With the Y-axis coordinate Ey of the node as an input parameter f (Ey) = Ds × Ey × sin θ / (K + Ey × cos
θ) + c1 where c1 is a constant g (Ey) = Ds / (K + Ey × cos θ), which stores a function table represented by two equations, and the bird's-eye view map display data creation circuit stores Sx = g (Ey) × Ex + c2 where c2 is a constant Sy = f (Ey) based on two equations, the data (Ex, Ey) of the position coordinates of the node on the road map is the bird's-eye view map display data (S
x, Sy). 9. The map display device according to claim 8, wherein the table storage circuit is the function table f (Ey).
And a plurality of sets of function tables paired with g (Ey), wherein the bird's-eye view map display data creation circuit is the final bird's-eye view map display data based on the result of conversion using the function table of each set. To create. 10. The map display device according to claim 9, wherein the display screen is divided into at least two areas, a first area near the current position of the vehicle and a second area away from the current position of the vehicle. , The conversion table has the function f (Ey) suitable for each of the first area and the second area.
And g (Ey) have first and second tables. 11. The map display device according to claim 5, wherein a road map data selection circuit that selects, as a coordinate conversion area, data of a road map in a predetermined range around the current position of the vehicle, and a road in the selected range. And a figure selection circuit for selecting a polygon or a link at least part of which is included in the map data, wherein the bird's-eye view map display data creation circuit sets the position coordinates of nodes belonging to the selected polygon or link, The bird's-eye view map display data is created based on the data converted into the position coordinates on the bird's-eye view map by the function table. 12. The map display device according to claim 10, wherein the nodes belonging to the polygons or links selected by the graphic selection circuit are outside the predetermined range selected by the road map data selection circuit. And a node position correction circuit for correcting the position coordinates of the extracted node to a predetermined position within the range selected by the road map data selection circuit. 13. A reading device for reading the planar map data from a storage medium storing planar map data of a road map, a current position detecting device for detecting a current position of a vehicle, and roads around the detected current position. The position coordinates of the nodes on the bird's-eye map when looking down the position coordinates of the nodes included in the map from the viewpoint set above the detected current position in a given direction, a given look-down angle, and a given spread angle. A storage circuit for storing a function table for converting into a function table, and read the data relating to the coordinate position of the node on the bird's-eye map by operating the conversion table according to the coordinate position of the node of the road map, and to the read data. Based on this, the vehicle-mounted natu Geshon apparatus.