JP2610998B2 - Drawing method of car navigation system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a map drawing method for car navigation, and more particularly to a map drawing method suitable for drawing a locus of a car on a map.

<Prior Art> There is an automobile navigation system using a CD-ROM as a storage means for storing map data. Such an automobile navigation system stores a large amount of map data on a CD-ROM, and is provided with a display device and a position measuring device for measuring the current position of the vehicle, and the like.
Mark indicating the current position of the vehicle (location cursor)
At a fixed position on the display screen,
The map data corresponding to the vehicle position is read from the CD-ROM, the map is drawn on a display screen, and the map is scroll-displayed according to the movement of the vehicle.

The map stored on the CD-ROM has a longitude width and a latitude width (for example, a longitude width of 7.5) that are appropriately sized according to the scale level.
Minutes, latitude width 5 minutes), roads, rivers,
Railways etc. are indicated by a set of coordinates of vertices expressed in latitude and longitude,
These drawings are performed by connecting the vertices in order with straight lines.

4 and 5 are explanatory diagrams of map data.
In the figure, the lower left position Pb is 139 ゜ 7'30 ”E, 35 ゜ 0′N
0 ", upper right position Pa is 139 ゜ 15'0" E, 35 緯 5'N
FIG. 5 shows a map of the area 0 ″, and FIG.
2 shows the map data, each of which is represented by the number of vertices and the latitude and longitude of each vertex. The latitude and longitude of each point are actually
It is expressed as normalized x, y coordinates where the longitude and latitude of the lower left position Pb are (0,0) and the longitude and latitude of the upper right position Pa are (1,1).

Now, car navigation has a function of displaying the traveling locus of one's own car along with a map. In such trajectory display, trajectory data that is an actual distance is obtained from the azimuth of the automobile and the number of rotations of the tire, and the trajectory is drawn on a map using the trajectory data. However, since the map is expressed in latitude and longitude as described above, in order to correctly draw the trajectory on the map, the map expressed in the longitude and latitude must be converted so that the distance is displayed correctly. Must. That is, conversion must be performed so that the length between any two points on the drawing map is a length corresponding to the actual distance. FIG. 6 is a conversion figure when a map of a predetermined longitude width and a predetermined latitude width is converted into a plane map in which distances are accurately drawn, and for convenience of description, a deformation from a rectangle (dotted line) is shown. And
As the latitude increases, the deviation from the rectangle increases.

Conventionally, longitude and latitude map data is converted to planar map data by the following formula so that the distance is accurately represented. That is, the following formula Xs = cos (Ymap) · 2πR · [(Xmap−Xc) / 360] · S (1) Ys = 2πR · [(Ymap−Yc) / 360] · S (2) The longitude and latitude data (Xmap / Ymap) at each point of the map is converted to the position data (Xs, Y
s). In equations (1) and (2), (Xs, Ys): the coordinate value on the projected screen, (Xc, Yc), the longitude of the screen center (car position),
Latitude R ··· Earth radius S ··· Scale (Xmap, Ymap) ··· Longitude and latitude of the vertex (point) on the longitude and latitude map. Xn, Yn), the longitude and latitude of the lower left corner of the map (Xb, Yb),
Expressing the longitude and latitude width of the map as (Xw, Yw), (Xmap, Ym
ap) is given by the following equation: Xmap = Xb + Xn.Xw Ymap = Yb + Yn.Yw FIG. 7 is an explanatory view of equations (1) and (2) for calculating Xs and Ys by considering the earth as a sphere. In equation (2), 2πR is the circumference of the earth, and (Ymap−Yc) is an automobile. position
This is the latitude angle between Pc (Xc, Yc) and the point of interest Pmap (Xmap, Ymap) (see FIG. 7A), and the latitude distance from the car position to the vertex is calculated by equation (2). It is clear. Also, R · cos (Yma
p) is the radius of the cutting circle CIR (see FIG. 7 (b)) when the earth is cut on a plane perpendicular to the earth axis EAX including the point of interest Pmap (Xmap, Ymap), and 2πR · cos (Ymap) is the cutting circle CIR
, (Xmap-Xc) is the longitude angle between the car position Pc (Xc, Yc) and the point of interest Pmap (Xmap, Ymap) (see FIG. 7 (b)), and is given by equation (1). The longitudinal distance from the vehicle position to the point of interest is calculated.

<Problems to be Solved by the Invention> However, since a conventional conversion formula (formula (1)) for converting a longitude-latitude map into a flat map capable of displaying an actual distance includes cos, each of the longitude-latitude points is different. This requires a cos operation for the conversion, so that the longitude-latitude-to-plane conversion cannot be performed at high speed, and the map drawing cannot be displayed at high speed in a short time. In particular, a map contains point data of tens of thousands of points, and conversion of equations (1) and (2) must be performed on all of these points, and the conventional method including cos does not allow high-speed drawing of the map. It is possible.

In view of the above, it is an object of the present invention to provide a map drawing method for vehicle navigation that can convert longitude / latitude map data into plane map data that can be displayed at an actual distance by performing a trigonometric function operation twice.

Another object of the present invention is to provide a map drawing method for automobile navigation that enables high-speed display of maps and trajectories.

<Means for Solving the Problem> According to the present invention, the above-mentioned problem is solved by the present position (Xc, Y
c) by means of longitude and latitude, means for converting a map of a region having a predetermined longitude width Xw and a predetermined latitude width Yw into a planar trapezoidal map normalized in the longitude direction using the current vehicle position, and obtained by the conversion. Means for drawing the displayed trapezoidal map and the current position of the vehicle on a display screen.

<Operation> The current position (Xc, Yc) of the vehicle is obtained in longitude and latitude, and a map of a region having a predetermined longitude width Xw and a predetermined latitude width Yw is converted into a planar trapezoidal map normalized in the longitude direction using the current vehicle position. Then, the flat trapezoid map and the current position of the vehicle obtained by the conversion are drawn on a display screen.

At the time of conversion to a planar trapezoid map, the ratio P ₁ of the difference between the upper side length and the lower side length of the planar trapezoid map to the lower side length and the normalized longitudinal length P ₂ of the trapezoid at the vehicle position are expressed by the following equation: P ₁ = 1−1 [cos (Yc + Yw / 2 ) / cos (Yc-Yw / 2)] obtained by P ₂ = cos (Yc), the current position of the vehicle (Xc, Yc), lower left latitude and longitude of the map (X _B, Y _B) the ratio P ₁ and using the longitude length P ₂ following equation _{Xs = P 2 · [1-} P 1 · (Yn-Ycn)] · 2πR · [Xmap -Xc] / 360] · S Ys = 2πR · the [(Ymap-Yc) / 360 ] · S Ycn = (Yc-Y B) / Yw Yn = (Ymap-Y B) / Yw ( where, R represents the earth radius, S is the scale), history on the map The degree data (Xmap, Ymap) is converted into position data (Xs, Ys) of a flat trapezoid map with the vehicle position (Xc, Yc) at the center of the screen.

If you do the above, only two times when generating a map image
By simply performing s calculation, all the longitude and latitude point data can be converted to planar trapezoidal map data by simple calculation and multiplication, and high-speed drawing of a map according to the actual distance becomes possible. Moreover, since the map is drawn according to the actual distance,
The traveling locus detected according to the actual distance can be accurately drawn on the map.

<Embodiment> FIG. 1 is a block diagram showing a navigation system for an automobile which can realize the present invention.

In the figure, 1 is a CD-RO serving as map data storage means
Reference numerals M and 2 denote operation units provided with various keys for searching for a map on a CD-ROM, enlargement / reduction, and the like. Reference numeral 3 denotes an azimuth sensor for detecting an absolute azimuth, and includes a geomagnetic sensor and a steering sensor. Reference numeral 4 denotes a movement amount sensor, which includes a vehicle speed sensor for detecting a traveling distance, a transmission sensor for detecting forward / backward movement, and the like. Reference numeral 5 denotes a position calculation CPU which calculates the current position (longitude and latitude) of the vehicle based on the values input from the direction sensor 3 and the movement amount sensor 4.

Reference numeral 6 denotes a processing unit, which has a system controller (CPU) 7, a map data buffer memory 8, and the like. The system controller 7 accesses the CD-ROM 1 based on a CD-ROM access command from the operation unit 2 or the current position of the vehicle input from the position calculation CPU 5 and reads out necessary map data. Further, the system controller 7 converts the read spherical map data in latitude and longitude representation into trapezoidal plane map data capable of displaying an actual distance and outputs the data to a subsequent display device. The image read address (window-position data) is input to the display device to scroll the map.

The map data buffer memory 8 stores the map data read from the CD-ROM 1. It is assumed that the map data can display a map having a size corresponding to a plurality of screens.

Reference numeral 10 denotes a display device, and a CRT controller 11,
It has a video RAM (VRAM) 12, a read control unit 13, a cathode ray tube (CRT) 14, and the like, and displays a desired map and cursor on the CRT.

FIG. 2 is an explanatory diagram of a conversion formula for converting a map having a predetermined longitude width Xw and a predetermined latitude width Yw into trapezoidal plane map data conforming to real distance display.

By the way, in the conventional methods of the formulas (1) and (2), as described above, a map having a predetermined longitude width and a predetermined latitude width is displayed on the screen as shown in FIG. This conventional method can display a map in accordance with an accurate real distance over the entire screen, but requires a cos operation accordingly. However, in the case of car navigation, it is not necessary to accurately display the actual distance on the entire screen, and even when displaying the traveling trajectory, it is sufficient if the distance is correctly drawn near the car. . Thus, in the present invention, a map having a predetermined longitude width and a predetermined latitude width is converted from a longitude-latitude map to a planar trapezoidal map as shown in FIG.

The conversion of the longitude / latitude map to the trapezoidal map is performed by the following formula. That is, the following equation: P ₁ = 1− [cos (Yc + Yw / 2) / cos (Yc−Yw / 2)] (3) P ₂ = cos (Yc) (4) Xs = P _{2. [1-P 1 · (Yn} -Ycn)] · 2πR · [(Xmap -Xc) / 360] · S ··· (5) Ys = 2πR · [(Ymap-Yc) / 360] · S ··· (6) Ycn = by _{(Yc-Y B) / Yw} ··· (7) Yn = (Ymap-Y B) / Yw ··· (8), the longitude and latitude data (Xmap, Ymap), car position ( X
c, Yc) is converted into position data (Xs, Ys) of a planar trapezoid map with the center of the screen. In the above equation, (Xs, Ys): the projected coordinate value on the screen, (Xc, Yc): the longitude and latitude of the car position, Xw, Yw, the longitude width of the area in the longitude and latitude map, latitude width (X _B, Y _B) ·· Coordinates radius S .. scale Coordinates R ... earth left lower position of the region in the map (Xmap, Ymap) of interest points in · Coordinates map longitude, latitude Ycn ··· The value representing the latitude of the car position in normalized xy coordinates, Yn ··· The value representing the latitude Ymap of the coloring point in normalized xy coordinates.

(3) Parameter P ₁ of the formula the difference trapezoidal upper length and a trapezoidal lower length, ratio trapezoidal lower length (4) is a car position (Xc, Yc) longitude length normalized trapezoidal in. (5) (Yn-Ycn) is latitudinal between interest points and car position normalized distance in _{formula, P 1 · (Yn-Ycn} )
Is the rate of decrease of the trapezoid width at the point of interest, and therefore, the longitudinal distance between the vehicle position Pc (Xc, Yc) and the point of interest Pmap (Xmap, Ymap) is expressed by equation (5). It is clear that the distance in the latitude direction is calculated from the position of the vehicle by the equation (6).

Therefore, when the car moves from the center position in the state shown in FIG. 2, the longitude and latitude map is set in the longitude direction according to the equations (3) to (8) so that the position of the moved car becomes the center of the screen (screen). The map is converted to a trapezoidal map that has been normalized to be displayed on the screen. In this case, (3),
If the cos operation is performed once to obtain P ₁ and P ₂ in the expression (4), each point Pmap (xmap, ymap) can be calculated by the expressions (5) to (8) without performing the cos operation. Can be converted to coordinate values (Xs, Ys) on the screen.

FIG. 3 is a flowchart of the process of the present invention. The map image is developed (stored) in the video RAM (VRAM) 12 in advance, and the map is scrolled on the display screen by moving the range (window) from which the map image is read from the VRAM according to the movement of the vehicle. The latitude and longitude map data corresponding to the drawn map image is stored in the buffer memory 8.

In parallel with the scroll display processing, it is checked whether the vehicle has moved a predetermined distance (step 101). When the vehicle has moved a predetermined distance, the current position data (longitude and latitude) of the vehicle is received from the position calculation PCU5, and the vehicle position data is obtained. (Xc, Y
Using c), the trigonometric function calculation of the equations (3) and (4) is performed once to calculate the parameters P ₁ and P ₂ (step 102).

Then, using the parameters P ₁ and P ₂ , (5), (6)
The latitude and longitude map data stored in the buffer memory and the latitude and longitude data of the point sequence points of the traveling locus stored separately are converted into planar trapezoidal map data by the formula and input to the display device 10 (step 103).

The display device 10 generates a map image using the input flat trapezoidal map data, stores the map image in the VRAM, reads the map image from the designated window, and scrolls and displays it on the CRT (step 104).

After that, every time a new movement is made by a predetermined amount, an image based on the map data obtained by converting the latitude and longitude to the plane trapezoid is stored in the VRAM and the map is scroll-displayed.

Incidentally, the error due to the map display of the present invention is a scale of 1/200000,
It is 0.004% of the conventional method in the case of latitude 35 °, and there is no practical problem.

<Effects of the Invention> According to the present invention, a map of an area having a predetermined longitude width and a predetermined latitude width is converted into a planar trapezoidal map so that the position of the vehicle is at the center of the screen. Is constructed so that a map according to the distance of the map is drawn on the screen, so when the map image is generated, the cos calculation is performed only twice, and all the longitude and latitude points are calculated by simple calculation and multiplication of the point data into a flat trapezoid. It can be converted to map data, and high-speed drawing of a map according to the actual distance becomes possible. Moreover, in the present invention, since the map is drawn in accordance with the actual distance, the traveling locus detected according to the actual distance can be accurately drawn on the map.

[Brief description of the drawings]

FIG. 1 is a block diagram of a car navigation system for realizing the method of the present invention, FIG. 2 is an explanatory diagram of a longitude-latitude map-plane trapezoidal conversion, FIG. 3 is a flowchart of the process of the present invention, and FIGS. FIG. 6 is an explanatory diagram of a planar map outline according to a conventional method, and FIG. 7 is an explanatory diagram of a conventional longitude / latitude map-plane conversion method. 1 ... CD-ROM, 5 ... CPU for position calculation, 7 ... System controller, 8 ... Map data buffer memory, 10 ... Display device,

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yukinobu Nakamura 1-4-1, Chuo, Wako-shi, Saitama Pref. Honda Technical Research Institute Co., Ltd. (56) References JP-A-62-214500 (JP, A)

Claims (3)

(57) [Claims] 1. A map represented by longitude and latitude is converted into a real-distance plane map and drawn on a display screen, and a mark indicating a current position of the vehicle is fixedly displayed at a fixed position on the display screen, and In the car navigation map drawing method of scrolling the map according to the movement, a current position (Xc, Yc) of the vehicle is obtained in latitude and longitude, and a predetermined longitude width Xw and a predetermined latitude width are determined using the current vehicle position.
Converting the map of the Yw area into a flat trapezoidal map normalized in the longitude direction, and drawing the flat trapezoidal map obtained by the conversion and the current position of the car on a display screen Method. 2. The conversion to the normalized planar trapezoid map is performed by: a ratio P ₁ of a difference between an upper side length and a lower side length of the planar trapezoid map to a lower side length; and a normalized longitudinal length P ₂ of the trapezoid at the vehicle position. determined by the following equation _{P 1 = 1- [cos (Yc} + Yw / 2) / cos (Yc-Yw / 2)] P 2 = cos (Yc), motor vehicle current position (Xc, Yc), lower left latitude and longitude of the map (X _B ,
Y _B), the following equation _{Xs = P 2 · [1-} P 1 · (Yn-Ycn)] using a ratio P ₁ and longitude length _{P 2 · 2πR · [Xmap -Xc} ] / 360] · S Ys = 2πR · [(Ymap-Yc ) / 360] · S Ycn = (Yc-Y B) / Yw Yn = (Ymap-Y B) / Yw ( where, R represents the earth radius, S is the scale), the map 2. The method according to claim 1, wherein the upper / lower latitude and longitude data (Xmap, Ymap) is converted into position data (Xs, Ys) of a planar trapezoidal map having the vehicle position (Xc, Yc) as the center of the screen. How to draw the car navigation described. 3. The method according to claim 1, wherein the position data indicating the trajectory of the vehicle obtained by accumulating the latitude and longitude of the current position is converted into position data of a flat trapezoid map and drawn together with the map. The map drawing method for car navigation described in the section.