GB2331685A

GB2331685A - Simulated movement over terrain

Info

Publication number: GB2331685A
Application number: GB9814957A
Authority: GB
Inventors: Kwang-Sung Shin
Original assignee: Daewoo Electronics Co Ltd
Current assignee: WiniaDaewoo Co Ltd
Priority date: 1997-11-20
Filing date: 1998-07-09
Publication date: 1999-05-26
Anticipated expiration: 2018-07-09
Also published as: KR19990040882A; GB9814957D0; GB2331685B

Abstract

A method for simulating the movement of a vehicle over a terrain is disclosed. The terrain is divided up into polygonal areas (in this case triangles) each associated with a graphical image or scene. The data for the whole terrain is stored in a database (106) of the individual mosaic s or tiles of the terrain. The method predicts the future position of the vehicle based upon its current position (108) and velocity (110) and selects likely cells from which the next scene frame will need to be generated. The image data corresponding to these predicted scenes is then passed to a processor (104). The method is applied to a video game driving simulator in the example given, to provide an animated graphical display. The advantage is that the use of a predictive position speeds up the process of providing images for display.

Description

-, 1 11 2331685 METHOD FOR FINDING A LOCATION OF AN OBJECT MOVING ON A

TERRAIN SURFACE REPRESENTED BY TRIGONOMETRIC GRIDS The present invention relates to a terrain tracer simulator; and, more particularly, to a method for finding a location of an object moving on a trigonometric grid which approximately represents a terrain by using a plurality of triangles.

A good exemplary application of a terrain tracer simulator technology is a video game simulating an auto driving. In such a video game, a terrain tracer simulator is is used to provide a mock view of a path along which the vehicle is driven as well as the scenery surrounding the path.

Information on the path and the scenery is converted into proper data to be stored in the terrain tracer simulator prior to the operation thereof. A technique approximating the contour of the scenery by using a polygonal grid has been employed in reconstructing the image of the path and the scenery. The polygonal grid is a network of a plurality of small planar polygonal patches, e.g., triangles.

In order to instantly and continuously display the path and the scenery with the movement of the vehicle, a prediction process is necessary to predict a next location of the vehicle 1 - is in a predetermined time interval ahead from a present time by using information on the present speed and direction of the vehicle. Following the prediction process, it is also necessary for the terrain tracer simulator to perform a selection process, i.e., deciding on which polygon in the polynomial grid the next location of the vehicle will lie.

For the terrain tracer simulator to provide a reliable display of the fast-passing path and scenery, the prediction and the selection processes must be performed within a predetermined time interval which typically is very short. Furthermore, the prediction and the selection processes usually involve a large volume of calculations. In particular, the time spent on the selection process is much longer than that of the prediction process.

Consequently, there has existed a need for a faster selection process capable of executing a large volume of calculations within a limited time to thereby achieve a highly efficient terrain tracer simulator.

It is, therefore, a primary object of the present invention to provide a method for deciding an exact location of a vehicle in a simpler and more efficient manner.

According to the present invention there is provided a method for deciding a triangle on which an object lies at a given moment, the triangle being an element of a 2 - trigonometric grid which approximately represents a terrain on which the object is traveling, the method comprising the steps of: (a) predicting a next location of the object after a predetermined time interval from a present time; (b) selecting K number of candidate triangles an which the next location is likely to lie based on the predicted next location, K being a positive integer; (c) setting a loop counter i to 1; (d) selecting an i-th candidate triangle from said K number of candidate triangles, i being an integer between 1 and K; (e) obtaining a set of decision indices with respect to the i-th candidate triangle; (ú) checking if each of the decision indices obtained at step (e) falls within a predetermined limit; (9) increasing the value of loop counter i by 1 and going back to step (d) if any of the decision indices does not fall within the predetermined limit; and (h) selecting the i-th candidate triangle as the triangle on which the object lies if each of the decision indices falls within the predetermined limit.

The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given with reference to the accompanying drawings, in which:

Fig. 1 depicts a simplified block diagram of a terrain tracer simulator to which the inventive method is applicable7 - 3 (3 1 1 is Figs. 2A and 2B show exemplary formats of data stored in a database; Fig. 3 illustrates an exemplary relationship between a point and the sides of a triangle for use in determining whether a point lies on the triangle; and Fig. 4 presents a flow diagram describing the inventive method.

A preferred embodiment in accordance with the present invention will now be described in detail with reference to Figs. 1 to 4.

Fig. 1 depicts a simplified block diagram of a terrain tracer simulator 100 to which the invention is applicable.

The terrain tracer simulator 100 comprises an input unit 102, a processor 104, a database 106, a location information provider 108 and a movement analyzer 110.

The input unit 102 serves to receive inputs from an operator or a driver, wherein the input may be a selection signal as to a terrain the operator wants to follow or a starting position of an object or a vehicle (not shown) to move about on the terrain. The starting position can be given a predetermined position in the absence of an input when starting the terrain tracer simulator 100.

The processor 104 controls the overall operation involved in the method in accordance with the present invention. For - 4 0 example, it receives instructions of the operator via the input unit 102, retrieves data representing the terrain, performs a prediction process, i. e., calculating a next location of the vehicle by using information on a present speed and direction of the vehicle, and also performs selection processes of deciding on which triangle within a trigonometric grid the next predicted location of the vehicle will lie, wherein the trigonometric grid approximates the terrain by using a plurality of triangles.

The database 106 serves for storing data for information on the trigonometric grid. The data stored in the database 106 is information on each of the triangles. Exemplary formats of the data stored in the database 106 are shown in Figs. 2A and 2B. As shown in Fig. 2A, the database 106 holds a vertex list, i.e., data for information on vertices employed in the trigonometric grid, and each vertex is represented by a value on each axis of a three dimensional coordinate system or XYZ coordinate system. For example, vertex 1 is expressed with three values, X,, Y1 and Z1. in the XYZ coordinate system. The storage area shown in Fig. 2B stores a triangle list which holds data for information on the triangles constituting the triangular grid, each of the triangles being represented by the three vertices thereof. For example, as shown in Fig. 2B, numbers 1, 7 and 10 represent the three vertices of triangle It is assumed that data for the information on the 0 is terrain is previously stored, before performing the inventive method, in the database 106 as shown in Figs. 2A and 2B.

The location information provider 108 is for predicting the next location of the vehicle and providing the processor 104 with the data on the next location.

The movement analyzer 110 monitors a movement of the vehicle to obtain information on the speed and direction of the -vehicle at a given time and provides the information thereon for the location information provider 108.

Fig. 4 illustrates the flow diagram describing the inventive method.

At step 402, the movement analyzer 110 monitors the movement of the vehicle to obtain the information on the speed and direction of the vehicle and provides the data for the location information provider 108.

At step 404, the location information provider 108 predicts the next location of the vehicle by using the data on the speed and direction transmitted from the movement analyzer 110 and provides the data on the next location to the processor 104.

The processor 104 selects candidate triangles by using the next location data at step 406. The candidate triangles are chosen so that the next location of the vehicle will lie on at least one of the candidate triangles, which can be supported by the assumption the predetermined time interval is chosen so short that the vehicle cannot move to a triangle 0 is that does not abut on the present triangle within the predetermined time interval. In the inventive method, the candidate triangles refer to triangles abutting on a present triangle on which the present location of the vehicle lies.

At step 408, the processor 104 sets a loop counter i to 1.

At step 410, an i-th candidate triangle is selected. In response to the selection, at step 412, the processor 104 retrieves data on a selected candidate triangle stored in the database 106, and, subsequently, by referencing the retrieved data, fetches the vertex data corresponding to the selected candidate triangle from the vertex list stored in the database 106. By using the vertex data, the processor 104 performs a series of calculations in order to obtain decision indices to determine whether the next location will lie on the selected i-th candidate triangle.

The series of calculations is performed as follows.

Referring to Fig. 3, there is illustrated an exemplary relationship between a point and the sides of a triangle. For the purpose of illustration, it is assumed that the next predicted location of the vehicle is point X which lies on triangle V,-V2 -V, having vertices V,, V, and V3.

The vertex data fetched from the database 106 has three values, V, / V2 and V3, each represented by a set of three coordinate values. A straight line containing the point X and parallel to a side of the triangle, e.g., a line segment V 2-V3 0 1 can be drawn as shown in Fig. 3. Accordingly, two points of intersection are obtained, one marked with X,. which is the intersecting point between the straight line and the line segment V,-V2, and the other marked with X2, an intersecting point between the straight line and the line segment V CV3' Points X, and X2 can be expressed by Eqs. 1 and 2:

X1 V1 + C ( V2 - V1) Eq. 1 wherein a is a parameter having a value between 0 and 1 and X2 ' V1 + V V3 - V1) Eq. 2 wherein Z is also a parameter having a value between 0 and If point X shown in Fig. 3 is assumed to be a point on the line segment X,-X 2 ' the equation with respect to the point X can be represented by Eq. 3:

X ' xl Y (X2 _xl) Eq. 3 wherein y is another parameter having a value between 0 and 1.

As can be seen from Eq. 3, point X is determined by points X, I X2 and parameter y. Substituting Eqs. I and 2 into 1,13 is Eq. 3 produces Eq. 4:

- C (1 _Y) Y) V1 + CC (1 _Y) V2 + P Y V3 X (I Eq. 4.

From the above, with a (1-y) = m and gy = n, Eq. 4 can be rewritten as:

X = v,. + m (V2 - v,) + n W, - v,) Eq. 5.

It is apparent that parameters m and n,each being referred herein to a decision index, range from 0 to 1, if point X lies on triangle V1-V2-Y3.

In order to obtain an equation expressed with respect to decision indices m and n, X-V, can be expressed as:

x- v, = m (v2- v,) + n (v, - v,) Eq. 6.

It should be noted that the y-axis values are excluded from consideration in deciding whether point X lies on the triangle V 1-V 2-V 3' which means that the slope of the triangle V 1 - V 2_ V 3 is disregarded. For the purpose of the decision making in accordance with the present invention, it can be regarded that the vehicle lies on the triangle V CV 2_ V 3 if point X lies on a projection of the triangle V1-V2-V3 onto the X-Z plane. The exclusion, therefore, simplifies the selection - 9 3 processes without sacrificing the accuracy. Consequently, only the x-axis and the z-axis values are considered in the series of calculations. Eq. 6 can then be rewritten with respect to the x-axis and z-axis, which yields Eqs. 7 and 8:

X-Vx = rn(vx-v -',,x) 1,x) + n (V, Eq. 7 X, - V, = M(V2Z-VIZ) + 3Z_ lz Z n (v v Eq. S.

Eqs. 7 and 8 can be rewritten in the form of a matrix equation as:

M) V 2x_V1X V3X_V1X '-X X V 12 V2Z_V1Z V3Z_V1Z XX.-Viz Eq. 9.

Now, solving Eq. 9 produces the values for the decision indices m and n, respectively.

Referring back to Fig. 4, it is checked whether each of the values of decision indices m and n falls within the range from 0 to 1 at step 414.

If both decision indices m and n are determined to be within the range from 0 to 1, point X is finally determined to lie on the selected triangle at step 418, which ends the procedure. However, if any one of decision indices m and n r \_ 1) is determined not to be within the range from 0 to 1, point X is determined not to lie on the selected triangle, and, then, the loop counter i is increases by 1 at step 416 and the procedure goes back to step 410 wherein another candidate triangle or the second candidate triangle is selected.

Steps 410 to 416 are repeated until it is determined that the object lies on a candidate triangle.

As described above, the method in accordance with the present invention is capable of deciding simply and effectively the triangle on which the moving vehicle will reach at a next moment.

While the present invention has been described with respect to the preferred embodiments, other modifications and variations may be made without departing from the scope of the present invention as set forth in the following claims.

is 11 - 0

Claims

Claims:

1. A method for deciding a triangle on which an object lies at a given moment, the triangle being an element of a trigonometric grid which approximately represents a terrain on which the object is traveling, the method comprising the steps of:

(a) predicting a next location of the object after a predetermined time interval from a present time; (b) selecting K number of candidate triangles on which the next location is likely to lie based on the predicted next location, K being a positive integer; (c) setting a loop counter i to 1; (d) selecting an i-th candidate triangle from said K number of candidate triangles, i being an integer between 1 and K; (e) obtaining a set of decision indices with respect to the i-th candidate triangle; (f) checking if each of the decision indices obtained at step (e) falls within a predetermined limit; (9) increasing the value of loop counter i by 1 and going back to step (d) if any of the decision indices does not fall within the predetermined limit; and (h) selecting the ith candidate triangle as the triangle on which the object lies if each of the decision indices falls within the predetermined limit.

3 is

2. A method according to claim 1, wherein step (a) includes the steps of:

(al) obtaining a current speed and direction of the object; and (a2) calculating the next location of the object by using the current speed and direction of the object.

3. A method according to claim 2, wherein the information on the predicted next location and on the vertices of the candidate triangles is represented by two-dimensional coordinate values, respectively.

4. A method according to claim 3,wherein the number of the decision indices is two, which are represented by the equation:

X. - VIZ (M) -v - v -1xx_Vix) 1 ( V2X IX V3X 1X n V2z_V1zV3z_V1z) wherein m and n are the decision indices; V1x' V2., and V3, represent the X-coordinate values of the vertices of the i-th candidate triangle, respectively; Xx is the X-coordinate value of the predicted next location of the object; V1z, V2z and V3,. represent the Z-coordinate values of vertices of the i-th candidate triangle, respectively; and Xz is the Zcoordinate value of the predicted next location of the object.

- __I

5. A method according to claim 4, wherein the number of the candidate triangles is 2.

6. A method according to claim 5,wherein the predetermined limit is any number between 0 and 1.

7. A method according to claim 6,wherein the triangles abutting on the triangle on which the vehicle lies at the present time are chosen as the candidate triangles.

8. A method according to claim 7, wherein each of the candidate triangles is identified by the X- and Z-coordinate values of the three vertices thereof.

9. A video display method comprising a method according to any one of the preceding claims and further comprising the step of displaying at least a portion of said terrain in dependence upon the selected i-th candidate triangle.

10. A method substantially as hereinbefore described with reference to figure 4 of accompanying drawings.

14