JPH0636013A - Method and device for generating topographic data - Google Patents

Abstract

PURPOSE:To provide the means which can displays a real image close to real topography on a display by computer graphics. CONSTITUTION:This computer graphics display method generates mesh data 1 by storing data on altitude values of the topography corresponding to intersections of a lattice obtained by dividing a two-dimentional plane at constant intervals and displays the topography on the display according to the mesh data 1; and a part where variation in the altitude of the topography becomes discontinuous is defined as ridge line data 2 and added to the mesh data 1 to generate graphic data 3 for the topographic display. The display which is real and fast can be obtained with the small topographic data. Further, adaptive mesh and ridge line division is performed corresponding to a change in view point to reduce the display data, thereby enabling even an increase in the speed of display processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer graphics technique suitable for landscape simulation and the like, which is a method for displaying three-dimensional topographical data modeled inside a computer on a display.

[0002]

2. Description of the Related Art A conventional method for displaying topographical data is described in, for example, Japanese Patent Laid-Open No. 3-75682.
It has elevation data at regular intervals in a grid pattern, and based on the data, it is converted into graphic elements such as triangles,
There is a way to generate an image of the terrain. Further, there has been a workstation system including an input device, a display device, a storage device, etc. as a means for generating such a topographic image.

[0003]

In the above-mentioned conventional technique, the elevation value data is sampled only at fixed intervals (for example, grid) on the terrain. For this reason,
The intersection of the grid where the data is stored (hereinafter referred to as "grid point")
Or, also referred to as "mesh points"), there may be a case where the terrain cannot be accurately represented when there is a rapid change in altitude. Even in such a case, if the number of divisions is increased in order to reduce the grid spacing, more accurate representation of the terrain can be achieved, but in this case, a significant increase in the amount of data becomes a problem.

Therefore, it has been expected to provide a method for suppressing the increase in the amount of data and displaying the terrain as accurately as possible.

Therefore, an object of the present invention is to provide a method for suppressing the increase in the amount of data and displaying the terrain as accurately as possible.

[0006]

Means for Solving the Problems In order to achieve the above object, the following means can be considered. As a first means,
A computer for storing the data of the elevation value of the terrain corresponding to the intersections of the grid obtained by dividing the two-dimensional plane into a grid at regular intervals, creating mesh data, and displaying the terrain on the display screen based on the mesh data. -In the graphics display method, the terrain that generates graphic data for terrain display is defined by defining ridge line data where the topographical height changes are discontinuous and adding the ridge line data to the mesh data. A method of creating data can be considered. Next, as a second means, the elevation value data of the terrain is stored in correspondence with the intersections of the grid obtained by dividing the two-dimensional plane into a grid at regular intervals to create mesh data, and based on the mesh data, In the computer graphics display method that displays the terrain on the display screen, the portion where the altitude change of the terrain is discontinuous is defined as ridge line data, and displayed for the display line segment created based on the ridge line data. A method of creating topographical data for generating graphic data for display is also conceivable so that the edge portion of the graphic data for is assigned. Further, in the first means, the size of the grid, which is constructed by having the intersections storing the mesh data, projected on the display screen is calculated, and the size is larger than a preset value. For the part, to create mesh data and ridge line data, the grid is repeatedly divided until the size becomes equal to or smaller than a predetermined size, and the geographical data for generating graphic data for display is created for the divided grid. A method is also possible. Further, in the first means, when the graphic data for display is generated, firstly, an area obtained by dividing the inside of the grid by the ridge line is obtained, and secondly, the area is used as a unit to divide into triangles. A method of creating topographical data using the triangle as a display graphic is also conceivable. In addition, in the first means, a portion in which a side of a certain figure is in contact with a vertex of another figure is detected as a T-vertex, and the T-vertex becomes a vertex of the triangle so that a triangle is created. A method of creating terrain data that allocates necessary vertices and creates graphic data for display is also conceivable.

As an apparatus for implementing the above method, the following means can be considered, for example. In a terrain data display device including an input means, a display means, an arithmetic processing means, and a data storage means, the storage means stores ridge line data which is data of a portion where the altitude change of the terrain becomes discontinuous. A device for creating topographical data, which is a means for doing so, can be considered.

[0008]

[Operation] The operation will be described below. The mesh data can represent the rough shape of the terrain. The mesh data is
The elevation value data of the terrain is stored and created in correspondence with the intersections of the grid obtained by dividing the two-dimensional plane into a grid at regular intervals. Next, the ridge line data is added to the portion where the topographical altitude changes become discontinuous, and the ridge line data is added to the mesh data. Ridge line data is used to represent characteristic parts of the terrain.

Therefore, by combining both the mesh data and the ridge line data, the display data which enables a good terrain display is created. In addition, since the ridge line data is the data that holds the elevation value linearly, it is mesh data,
The amount of data increases less than the reduction of the grid spacing.

The topography may be displayed based on the above data.

Further, the size of the grid, which has intersections storing the mesh data, projected on the screen is calculated, and the size of the grid is larger than a preset value. In order to create the mesh data and the ridge line data, it is possible to use a process of repeatedly dividing the grid until the size becomes equal to or smaller than a predetermined size and generating graphic data for display on the divided grid. By this processing, the grid is divided finely in the area close to the viewpoint and large in the area far from the viewpoint, so that the terrain display matching the human interval can be performed. Further, it is possible to suppress the increase in the number of data in the area far from the viewpoint. The actual graphic display process is performed as follows, for example. That is, when the graphic data for display is generated, first, an area obtained by dividing the inside of the grid by the ridge line is obtained, and secondly, the area is divided into triangles to display the triangle. It suffices to perform a process for forming a figure.

Since the addition of the ridge line data causes a new T-vertex, it is necessary to process it. The "T vertex" means a portion where a side of a certain figure is in contact with a vertex of another figure, and if appropriate processing is not applied to this, a gap is generated between the figures. In this case, the T vertex is detected, and the T vertex becomes a vertex of the triangle.
All that is necessary is to allocate the vertices necessary for creating the triangle and perform processing so as to create the graphic data for display. By performing the above processing, it is possible to suppress the amount of data and display the terrain with high accuracy.

[0013]

First, an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows ridge line data 2 as an outline of the present invention.
Is added to display data 3 together with mesh data 1.
Is created. The mesh data is data of elevation values of the terrain recorded at regular intervals. In the figure, the two-dimensional plane is divided into grids, and at each grid point, the altitude at that point is stored as data. I shall. On the other hand, the "ridge line data" is expressed by connecting discontinuous portions of altitude change with a line, and corresponds to a so-called mountain ridge. Of course, similarly, it is possible to define a portion corresponding to a valley as a valley line, but since it is not necessary to distinguish between a ridge and a valley in the following processing, in the present invention, the ridge line including the valley line is included. I will call it. Further, it is assumed that the ridge line data also records the data of the elevation value at a predetermined point through which the ridge line passes.
Further, as a condition for defining the ridge line, it is assumed that the ridge lines do not intersect with each other. As a method of inputting data regarding the ridge line, for example, a method in which an operator recognizes and defines the ridge line from a stereo photograph by aerial survey is considered. In the present invention, the ridge line data is added to the mesh data, and the terrain is represented by these data. Then, the display data to be displayed on the display or the like will be finally expressed by an aggregate of “triangles”. At this time, a process for assigning triangles is performed so that the ridge lines become the edges of the triangle and the ridge line shape appears.

Next, the processing according to the present invention will be described in detail with reference to the flow chart 1 of FIG. First, step 10
1 inputs altitude data. Details of the processing in this step are shown in the flowchart 2 of FIG. In FIG. 3, first, in step 1011, mesh data is input. For example, the process of inputting the data of the elevation value on the grid point from a data file or the like is performed. Step 101
In 2, the ridge line data is input, and the plane position of the ridge line, the elevation value data, and the like are input from a file or the like. In step 1013, the ridge line data is “mesh corrected”.
This correction method is shown in FIG. The points indicated by black triangles in the figure are
At the point where the elevation data of the ridge line is input, it usually does not match the mesh interval of the mesh data. Therefore, in order to facilitate the subsequent processing, the plane position that crosses the mesh grid is calculated, and this point is defined as the ridge point. Similarly, the altitude value is also obtained by linear interpolation of the altitude value data at the front and back points, for example. The ridge line data after "mesh correction" is obtained by connecting the ridge points thus obtained, and this data will be used thereafter. In step 102 of FIG.
It shows that the following steps are repeated for each viewpoint position. In the conventional CG (Computer Graphics) technology, when displaying a complicated shape, a method is known in which necessary minimum display data is held by adapting to display conditions. For example,
When a certain curved surface is displayed, it is divided into a set of quadrilaterals and approximated, and the quadrilaterals are used as three-dimensional display data.

In the field of computer graphics,
These display data are projected on a two-dimensional screen to generate an image. At the time of projection, the display data is sampled at the position of each pixel on the screen to determine the figure to be displayed. At this time, if the curved surface is divided so that each quadrangle has a size of, for example, 1/2 pixel or less on the screen, the Nyquist limit at the time of sampling (the minimum necessary division for reproducing the original continuous figure) Since the size is larger than, the perfect curved surface can be expressed even by using the quadrilateral approximation. The method of changing the division degree of the display figure according to the size projected on the screen is referred to as "adaptive division", and more specifically, for example, ACM Computer Graphics Vol.21, No.4. , 1987 7
Issued monthly (ACM Computer Graphics, Vokume 21, Number
4, July 1987) page 97, etc. That is, C
When a G (Computer Graphic) animation is produced, every time the viewpoint position is changed, the following process of mesh (lattice) division is performed. Details of the mesh division processing in step 103 will be described in the flowchart 3 of FIG.
And shown in FIG. First, in step 1031 of FIG. 4, it is shown that the mesh division is repeated on the screen until the mesh becomes sufficiently small. As shown in FIG. 9, the mesh data is finally perspective-projected and displayed on the screen of the display. However, in the figure, for the sake of explanation, the figure is such that altitude data is ignored. Here, if the viewpoint position is as shown in the same figure, in perspective projection, a portion close to the viewpoint is displayed large and a portion far from the viewpoint is displayed small. Therefore, even those that appear small on the screen,
It is not necessary to prepare the display data with the same accuracy. Therefore,
In a region far from the viewpoint, mesh points are thinned out to prepare a so-called "adaptive division" mesh data corresponding to the viewpoint change. Similarly, for ridge line data, ridge points far from the viewpoint are thinned out. Step 10 of FIG.
In 32, one mesh (lattice) is subdivided into four. This is "Q in the field of image processing.
This is the same as the division method of the image description method called "uad Tree", and is a method of recursively dividing the mesh into four at midpoints in the x and y directions. Step 1033 shows a process of perspectively projecting the positions of the mesh points at the four corners of the mesh onto the screen. This perspective projection transformation equation is generally well known, and x '= x / z and y' = y / as shown in, for example, "Applied Graphics" (published by ASCII Corporation, P64). The conversion process is performed using the expression z. Where x ′ and y ′ are
The position on the screen, x, y, z represents the position where the grid point is defined in space. Since the position where the grid point is projected on the screen can be known by such conversion, in the next step 1034, the size of the mesh projected is calculated. Here, the size of the mesh may be determined by calculating the value of the length of the diagonal line of the projected mesh points, for example. When this value is larger than the threshold value specified by the user in advance, the division into four is performed again. Step 104 in FIG. 2 indicates that the processes performed in the following steps are repeated for each mesh (lattice) after mesh division. FIG. 5 shows details of the processing in the vertex detection step of step 105.
4 and FIG. 10. First, in step 1051 of FIG. 5, the coordinates of mesh points are detected.
For example, from the information obtained when the mesh is divided, the mesh is x = x1, x = x2, y = y1, and y = y2.
It is assumed that the area is surrounded by. Next, the elevation value data corresponding to the four mesh points is also extracted from the already input mesh data. Next Step 10
At 52, the coordinates of the ridge point are detected. As for the ridge line, it is possible to specify the ridge line that passes through the above-mentioned region from the x and Y coordinate values thereof, so that the data of the elevation value is similarly extracted. Next, in step 1053, the coordinates of the so-called T vertex are detected. The “T vertex” is a portion where the side of a polygon (polygon) is in contact with the vertices of another polygon. As is well known, if such T vertices are directly converted into display data such as triangles, a gap may occur between the triangles at the time of display due to an error at the time of scan conversion, and the figure may become distorted. In order to avoid this phenomenon, the T-vertex is not a so-called polygonal corner point, but must be treated as a vertex. In the case like the present invention, there are two types of causes of the T vertex. The first is by mesh division, and the second is by addition of ridge line data. Here, FIG. 11 shows a pattern of T vertex generation by mesh division. At the time of mesh division,
When the meshes have different degrees of division between adjacent meshes, T vertices occur. For example, at a certain division level, among the four meshes to be further subdivided,
T vertices occur in the case where only one to three meshes are subdivided. There are four patterns of occurrence as shown in FIG. Therefore, the coordinates of the T vertex can be detected by examining the structure when the mesh is divided. On the other hand, FIG. 8 shows a case where the T vertex is generated by adding the ridge line data. That is, at the start and end points of the ridge line, T vertices are generated for adjacent meshes (lattices). Therefore,
On the adjacent mesh, the starting point of the ridge line, or
The coordinates of the T vertex can be detected by checking the presence or absence of the end point.

In step 106 of FIG. 2, a process of dividing each mesh (lattice) into polygons is performed. Details of the processing are shown in the flowchart of FIG. 6 and FIG. In step 1061 of FIG. 6, it is determined whether or not a ridge line exists in the mesh. If there is no ridge line, no special processing is done. Step 1062 indicates that the polygon division process is repeated for the ridge lines in the mesh. The term "polygon" in the present invention refers to a region divided in the mesh by a ridge line. Therefore, generally, the vertices of these polygons are not on the same plane and are not true polygons. A polygon division processing method will be described with reference to FIG. 12 by taking as an example a case where two ridge lines pass through the mesh. Step 106
In step 3, the polygon is redivided into two regions for each ridge line. First, considering the case where only the ridge line 1 passes, the inside of the mesh is divided into two regions, polygon 1 and polygon 2. Next, ridge line 2
Is passed, only the inside of the polygon 2 is subdivided into two, and is divided into a polygon 2-1 and a polygon 2-2. In the subsequent processing, it is necessary to check the vertices belonging to each polygon, so that processing is performed in step 10.
At 64. In this method, it is determined by checking which of the two regions the vertex is divided by the ridge line. For example, in the example of FIG. 12, the mesh point 1 and the mesh point 3 are on the same side of the ridge line 1 as the origin in the x and y coordinates. That is, it is the apex of polygon 1. Also,
Mesh point 2, mesh point 4, ridge point 3, ridge point 4, and T vertex 1 are the vertices of polygon 2 because they are on the opposite side of the origin. Furthermore, ridge point 1 and ridge point 2
Is a point on the ridge line 1 and is therefore the vertex of both polygon 1 and polygon 2. In this way, the mesh can be divided into polygons and the vertices belonging to them can be determined.

Step 107 in FIG. 2 means that the processing in the following steps is repeated for each polygon. In step 108, each polygon is divided into triangles for display. Details of this processing are shown in the flowchart 6 of FIG. 7 and FIG. Figure 7
Step 1081 is a process of determining the presence / absence of a T vertex for the polygon. Since all the vertices belonging to the polygon have already been calculated, T
Detect vertices. Like polygon 2-1 in FIG. 13, T
If a vertex exists, this T vertex is set as a starting point in step 1082. If there is no T-vertex like polygon 1, step 1083 is performed.
At, processing is performed with the ridge point or mesh point as the starting point. Next, in step 1084, vertices other than two adjacent points on the left and right of the start point are set as end points. Further, step 10
At 85, division processing into triangles is performed by connecting the start point and all end points. Here, since the ridge lines have a condition that they do not intersect with each other, the generated polygon is a so-called convex polygon. In a convex polygon, a certain vertex is the starting point, and the remaining vertices except the adjacent points are the ending points,
Triangulation is possible by connecting all the start points and end points. However, when there is a T vertex, this is preferentially used as the starting point. If such a process is not performed, for example, when a point adjacent to the T vertex is selected as a starting point, a triangular vertex is not assigned to the T vertex, which causes a problem such as a gap when displaying the terrain.

Step 109 in FIG. 2 means that the processing in the following steps is repeated for each divided triangle. In step 110, a rendering process for displaying the generated triangle data on the display is performed. For example, as is commonly done,
It is possible to display the terrain data on the display by performing the hidden surface processing of the triangle by the Z-buffer algorithm.

The above-mentioned various processing methods are carried out, for example, by the following hardware.

For example, a terrain data display device having an input means, a display means, an arithmetic processing means, and a data storage means, wherein the input means is a portion where the altitude change of the terrain becomes discontinuous. Is a means for inputting ridge line data, mesh data, various commands, processing programs, etc.,
Further, the data storage means is a device which is means for storing ridge line data, mesh data, a processing program, a processing result and the like. Such an apparatus can be realized by a commercially available workstation, personal computer or the like. As described above, according to the present invention, by newly using ridge line data, it is possible to realize highly accurate topographical display while suppressing a significant increase in data. In addition, by adaptively performing mesh and ridge line division in response to a change in viewpoint, display data can be reduced, and display processing can be speeded up.

[0021]

[Effects of the Invention] Even if the intervals of mesh data are rough, ridge lines and valleys can be faithfully reproduced by the ridge line data, so that there is an effect that realistic terrain expression can be expressed with a small amount of data.
In addition, there is an effect that the mesh and ridge line division are adaptively performed in response to the change of the viewpoint to reduce the display data and speed up the display processing.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of mesh data with ridge lines.

FIG. 2 is a flow chart for explaining an embodiment of the present invention.

FIG. 3 is a flow chart for explaining an embodiment of the present invention.

FIG. 4 is a flow chart for explaining an embodiment of the present invention.

FIG. 5 is a flow chart for explaining an embodiment of the present invention.

FIG. 6 is a flow chart for explaining an embodiment of the present invention.

FIG. 7 is a flow chart for explaining an embodiment of the present invention.

FIG. 8 is an explanatory diagram of mesh data and ridge line data.

FIG. 9 is an explanatory diagram of adaptive division processing of mesh data.

FIG. 10 is an explanatory diagram of types of vertices.

FIG. 11 is an explanatory diagram of a pattern of T vertex generation by mesh division.

FIG. 12 is an explanatory diagram of polygon division processing.

FIG. 13 is an explanatory diagram of triangulation processing.

[Explanation of symbols]

1 ... Mesh data, 2 ... Ridge line data, 3 ... Display data

Claims (6)

[Claims] 1. Terrain elevation value data is stored in correspondence with intersections of a grid obtained by dividing a two-dimensional plane into a grid at regular intervals to create mesh data, and the terrain is displayed on a display screen based on the mesh data. In the computer graphics display method for displaying, the ridge line data is defined as the portion where the altitude change of the terrain becomes discontinuous, and the ridge line data is added to the mesh data,
A method of creating terrain data, characterized by generating graphic data for terrain display. 2. Terrain elevation value data is stored corresponding to intersections of a grid obtained by dividing a two-dimensional plane into a grid at regular intervals to create mesh data, and the terrain is displayed on a display screen based on the mesh data. In the computer graphics display method for displaying, the part where the altitude change of the terrain is discontinuous is defined as ridge line data, and the display line segment created based on the ridge line data is displayed as a graphic for display. A method of creating topographical data, characterized in that graphic data for display is generated so that the edge portion of the data of (1) is assigned. 3. The method of creating terrain data according to claim 1, wherein a grid constituted by intersections storing mesh data is projected on a display screen, and the size is calculated. However, in order to create mesh data and ridge line data for a portion larger than a preset value, the grid is repeatedly divided until the size becomes equal to or smaller than a predetermined size, and the divided grid is used as a target for display. A method for creating topographical data, characterized by generating graphic data. 4. The method for creating topographical data according to claim 1, wherein when generating graphic data for display, first, an area obtained by dividing the inside of the grid by a ridge line is obtained, and secondly, the area is divided. A method for creating topographical data, characterized by dividing a triangle into units and using the triangle as a display figure. 5. The method of creating terrain data according to claim 1, wherein a portion in which a side of a certain figure is in contact with a vertex of another figure is detected as a T vertex, and the T vertex is a vertex of a triangle. A method of creating topographical data, characterized by allocating the vertices necessary for creating triangles and creating graphic data for display. 6. A terrain data display device comprising an input means, a display means, an arithmetic processing means and a data storage means, wherein the storage means is data of a portion where the altitude change of the terrain becomes discontinuous. An apparatus for creating topographical data, characterized by being means for storing ridge line data.