JP2007041692A - Three-dimensional geographical data controller and three-dimensional geographical data control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a three-dimensional geographical display device having an LOD (Level Of Detail) function for more speedily plotting three-dimensional graphical data while keeping its display quality highly precise. <P>SOLUTION: This three-dimensional geographical data controller is provided with a three-dimensional graphical data reading part for reading three-dimensional graphical data, a three-dimensional graphical data storing part for storing the read three-dimensional graphical data, a significant geography designating means for designating a significant geographical structural part, a significant geographical information storing part for storing the designated significant geographical information, a scene control part for controlling the position of a visual point, the direction of the line of sight and the angle of field or the like automatically or by the operation of a user, a geographical LOD control part for generating a polygon to be plotted by selecting vertex data to be displayed by using a distance from the position of the visual point determined by the scene control part and the significant geographical information stored by the significant geographical information storing part and a three-dimensional geography plotting part for plotting the polygon generated by the geographical LOD control part into the three-dimensional geography by a computer graphics function. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a three-dimensional terrain data control method and a three-dimensional terrain data control apparatus for obtaining a three-dimensional terrain display image by computer graphics or the like in order to visualize three-dimensional terrain data.

  In general, as shown in Japanese Patent Laid-Open No. 61-148576 (Patent Document 1), a three-dimensional terrain display device is a ground surface in which altitude data corresponding to lattice coordinate points and distortion called an ortho image are corrected. A virtual terrain display is performed on a computer screen by a computer graphics function for drawing a texture image on a triangular polygon using an image.

  At this time, in order to give a more realistic feeling, a three-dimensional terrain display image similar to the real world is obtained by perspectively projecting a three-dimensional space viewed from a given viewpoint onto a projection plane. When perspective projection transformation is performed in which the image projected on the projection screen is displayed on the computer screen, objects close to the viewpoint are drawn large, and objects far away are drawn relatively small, as in perspective in painting. The If the line of sight is set vertically from the sky, the displayed ground surface distance will be almost uniform, but if the line of sight is set to be almost horizontal, it will be displayed from very close to far away. Become. Displaying far away requires calculation and display of more three-dimensional terrain data, resulting in an increase in processing load.

The workaround for this problem is to have a grid-like coordinate point data in a hierarchical structure for each grid size, using only coarser grid point data for distant coordinate data, and a fine grid for the neighborhood. A method using point data is known. In the above-mentioned patent document 1, there is a description of a method of increasing the number of grid points in the X and Y directions for each layer to make it multi-layered, and gradually roughening the layered terrain data.
A method of controlling the fineness of terrain data according to the distance from the viewpoint is a kind of computer graphics technology generally called LOD (Level Of Detail). This technique aims to reduce the drawing processing load while suppressing deterioration of drawing quality. The LOD technique in the three-dimensional terrain display technique includes an ortho image treated as a texture in addition to the terrain data. Japanese Patent Application Laid-Open No. 7-271999 (Patent Document 2) discloses one method for smoothly connecting a rough region and a fine region without gap when performing topographic data LOD.

In addition, when LOD hierarchical data is generated by spatially reducing the grid-like topographic data, there is a problem that the shape of the coastline, the top of the mountain, or the ridge is not maintained. In Japanese Patent Laid-Open No. 9-6941 (Patent Document 3), when the terrain is simplified by LOD using attribute types such as sea, land, lake, and mountaintop for each apex, the sea surface is pulled to the altitude on the land side. It is disclosed a method for calculating altitude data so that the height of the summit is not lowered.

  On the other hand, when a triangular polygon is represented based on grid-like topographic data, there is a characteristic that it is difficult to represent features that are continuous in directions other than 0 degrees, 90 degrees, 180 degrees, 270 degrees, 45 degrees, and 225 degrees. If the lattice size is reduced, the amount of data will increase rapidly, although it will be close to accurate representation. Japanese Patent No. 2875884 (Patent Document 4) discloses a method having data representing a characteristic portion separately from the grid-like topographic data in order to express a feature quantity continuous in an arbitrary direction.

JP-A-61-148576 Japanese Unexamined Patent Publication No. 7-271999 Japanese Unexamined Patent Publication No. 9-6941 Japanese Patent No. 2875884

In recent years, surveying accuracy has improved, and it has become possible to create a wide range of detailed 3D terrain data. In addition, display devices are rapidly becoming finer, and accordingly, a system for displaying a large amount of three-dimensional terrain data with higher speed and higher accuracy is required.
The conventional three-dimensional terrain display data control method has been able to realize the LOD function using grid-like terrain data. However, when handling terrain data with higher accuracy, the spatially uniform grid-like arrangement is used. Since the data amount is too large, it is necessary to use a more efficient three-dimensional terrain data format such as a TIN (Triangulated Irregular Network) format. In this case, there is a problem that the LOD function cannot be realized efficiently.

In the conventional three-dimensional terrain display, LOD control using continuity of the terrain is performed, and it cannot cope with a rapid change, resulting in deterioration of display quality. As the accuracy and level of detail of terrain data increase, relatively rapid changes and complex structures tend to increase.
The present invention has been made to solve the above-described problems, and is a three-dimensional terrain having an LOD function for rendering high-precision three-dimensional terrain data at a higher speed while maintaining display quality. The object is to provide a display device.

The three-dimensional landform data control apparatus related to this invention is
3D terrain data reading unit for reading 3D terrain data, 3D terrain data holding unit for holding the read 3D terrain data, and important for specifying important terrain structure parts from the stored 3D terrain data A terrain instruction means, an important terrain information holding unit for holding designated important terrain information, a scene control unit for controlling a display scene projected on the screen by a viewpoint position, a viewing direction, and an angle of view, and projecting on the screen The density of the 3D terrain data held by the 3D terrain data holding unit is controlled according to the size of the terrain LOD control unit for generating polygons, and the polygon generated by the terrain LOD control unit is a computer graphics function. A three-dimensional terrain drawing unit for drawing on the three-dimensional terrain, and the terrain LOD control unit includes a distance from the viewpoint position determined by the scene control unit, By using significant topographical information held in the main topographical information holding section, it is the arrangement for generating the polygons selected drawing vertex data of the three-dimensional topography data to be displayed.

In addition, the three-dimensional landform data control method according to the present invention is
A reading process for reading 3D terrain data in the 3D terrain data reading unit, a holding process for holding the read 3D terrain data in the 3D terrain data holding unit, and an important terrain structure part from the held 3D terrain data Important terrain instruction process that specifies the important terrain information holding process that holds the specified important terrain information in the important terrain information holding part, and the display scene projected on the screen is controlled by the viewpoint position, line-of-sight direction, and angle of view Generated by a scene control process, a terrain LOD (Level Of Detail) control process that controls the density of 3D terrain data in the 3D terrain data holding unit that draws according to the size projected on the screen, and a terrain LOD control process A three-dimensional terrain drawing process for drawing the polygons on the three-dimensional terrain by a computer graphics function. In the terrain LOD control process, And the distance from the viewpoint position determined by using the key terrain information stored in the key terrain information holding unit, and generates a polygon that selects the vertex data drawing to be displayed.

  According to the present invention, in LOD control for controlling the roughness of vertices for drawing high-precision three-dimensional terrain data to be drawn according to the distance from the viewpoint, information indicating a portion where the terrain structure is particularly desired to be retained is used. In addition, since the priority not to reduce the vertices corresponding to the part where you want to keep the terrain structure at the time of vertex data reduction, the important terrain structure can be accurately and quickly moved even if the viewpoint position is moved. It is possible to display. Therefore, when the present invention is applied to various simulation devices such as a flight simulator and a driving simulator, a display system for disaster prevention monitoring, and a computer game device, more realistic and accurate three-dimensional landform display can be performed at high speed.

Embodiment 1 FIG.
FIG. 1 shows the configuration of a three-dimensional terrain data control apparatus according to Embodiment 1 of the present invention. In FIG. 1, the 3D terrain data reading unit 200 receives 3D terrain data and ortho images represented in various formats from different files and the like. Conversion for holding in the terrain data holding unit 201 is performed in an internal format handled by the terrain data control device. The three-dimensional terrain data holding unit 201 manages and holds the terrain data shaped by the terrain data reading unit 200.

  In the field of map and terrain display, the edge of terrain and structures is called a break line, and is treated as a unique area on a continuous ground plane. A breakline information input unit 202 as an important terrain instruction means receives breakline information important as a terrain structure from the 3D terrain data held in the 3D terrain data holding unit 201 by the user, and this information holds the important terrain information. It is held in the break line information holding unit 203 as a unit. At this time, the input breakline information corresponds to the apex of the three-dimensional terrain data.

The scene control unit 204 determines a scene to be displayed on the screen based on parameters such as a viewpoint position and a viewing angle line-of-sight direction, automatically or by user input. The terrain LOD control unit 205 is based on the scene information generated by the scene control unit 204, and the three-dimensional terrain data held in the three-dimensional terrain data holding unit 201 according to the distance from the viewpoint position, that is, the size projected on the screen. Control the density of the three-dimensional terrain image to be drawn from, and use the important terrain information held in the breakline information holding unit 203, that is, the breakline information to select the vertex data to be displayed and display polygon data to be drawn Generate.
The polygon data generated by the terrain LOD control unit 205 is drawn as a terrain image by the three-dimensional terrain drawing unit 206.

FIG. 2 is a diagram for explaining the format of the three-dimensional terrain data. In the figure, 1 to 11 represent coordinate points and have real space coordinate data. The coordinate data is, for example, latitude, longitude, and altitude, or a combination of X, Y coordinates and altitude information.
In general, in computer graphics, a solid in a three-dimensional space is represented by a set of polygonal planes. In many cases, triangles (triangles) are used as polygons. One polygon 20 is defined by three vertices of coordinate points 1, 2, and 3. Similarly, the terrain is expressed by defining one polygon at coordinate points 1, 3, and 4 and one polygon at coordinate points 4, 3, and 10.

  An example of how to hold the 3D terrain data in the 3D terrain data holding unit 201 at this time is shown in FIG. The vertex buffer 100 holds coordinate point information. The index buffer 101 holds a set of coordinate points constituting the polygon as a list. One coordinate point is shared by a plurality of polygons. In the case of simple mesh data, with the exception of the end, one vertex (coordinate point) is used for six polygons, but there is no fixed value in the case of the TIN data format.

  FIG. 4 is a diagram for explaining the relationship between the break line and the terrain data according to the first embodiment of the present invention. A straight line connecting vertices indicated by 30 to 38 in the figure represents a specified break line. The break line information holding unit 203 associates the break lines that follow 30 and 31 with the vertex buffer 100 of the three-dimensional terrain data holding unit 201 and holds the information as the information that follows the vertex 1, vertex 4, and vertex 11. FIG. 5 shows an example of expressing the associated information. The break line list 102 manages the connection of continuous break lines in a list form, and allows a plurality of break line information to be managed.

In order to describe the LOD control operation according to the first embodiment of the present invention, FIG. 6 shows a conventional vertex reduction example that does not use breakline information. For example, it is assumed that the vertices 40, vertices 42, and vertices 44 expressed by white circles are selected by the vertex omission selection algorithm to reduce the number of drawn polygons and become vertices to be omitted. In such a case, when the vertex 40 and the vertex 42 are omitted, edges between polygons such as sides 41 and 43 are newly generated. However, in the example of this figure, there is no large positional shift. An algorithm for selecting a vertex to be omitted may employ a method of evaluating the distance between the omitted vertex and the polygon surface after the omission. In such a case, the influence of vertex reduction is small in the vicinity of the vertex 40 and the vertex 42. It can be said.
On the other hand, at the vertex 44, the break line 45 that is originally to be stored as information disappears, and completely different edges 46 to 48 are generated. In such a case, the effect of omission of vertices may greatly affect the image quality. For example, a phenomenon that a road or a track is bent and displayed is generated.

  FIG. 7 is a diagram for explaining LOD control using breakline information. LOD control omission by the vertex omission selection algorithm When selecting vertices, important terrain using breakline information important as the terrain structure specified by the breakline information input unit 202 and held in the breakline information holding unit 203 While maintaining the structure, the number of drawn polygons is reduced and high-speed display is performed. Although the total number of polygons is greatly reduced by the omitted vertices represented by white circles in the figure, the vertices of the break line portions of the sides 30 to 38 are omitted by the break line information held in the break line information holding unit 203. Therefore, when the terrain LOD control unit 205 generates polygon data, it is not affected by the reduction in the number of drawn polygons.

  As described above, according to the first embodiment of the present invention, in the LOD control process in which the terrain LOD control unit 205 reduces the number of drawn polygons far from the viewpoint position according to the viewpoint position, the break line information holding unit 203 Using the breakline information held in, the important terrain structure can be saved, and the display process can be improved while displaying highly accurate terrain data information.

Embodiment 2. FIG.
FIG. 8 shows the configuration of a three-dimensional landform data control apparatus according to Embodiment 2 of the present invention. This embodiment uses vector information different from three-dimensional terrain data as information for specifying an important terrain structure, and provides a vector information input unit 207 instead of the breakline information input unit 202 as an important terrain instruction means. is there. In the following description, the description of the same part as in FIG. 1 is omitted.

  In recent years, information relating to maps and terrain displays has been databased and filed in various formats and used for various uses. The vector information input unit 207 reads vector information of the same area as the 3D terrain data read by the 3D terrain data reading unit 200 from another file, and the user designates vector information of important terrain structure. For example, for roads, rivers, coastlines, lake shorelines, etc., the effect of omission of vertices greatly affects the image quality, and the omission of vertices causes such a phenomenon that they are bent and displayed as shown in FIG. Therefore, these are important terrain structures, and the vector information is converted by the vector information input unit 207 according to the coordinate system of the three-dimensional terrain data used in the three-dimensional terrain data control device. The vector information holding unit 208 holds the vector information read by the vector information input unit 207 and converted according to the coordinate system of the three-dimensional terrain data. The shape holding area determination unit 209 recognizes the space in the vicinity of the coordinates obtained from the vector information as the shape holding area, and determines that the degree of importance is high when the inquired vertex is within the shape holding area. Returns the result.

  The terrain LOD control unit 205 is based on the scene information generated by the scene control unit 204, and the three-dimensional terrain data held in the three-dimensional terrain data holding unit 201 according to the distance from the viewpoint position, that is, the size projected on the screen. The density to draw is controlled, and vertices to be omitted are selected. The selected retention target vertex is inquired of the shape holding area determination unit 209 about its importance, and if it can be determined that it can be omitted from the returned importance information, the vertex is omitted, and the display polygon data to be drawn is determined and displayed. Generate.

FIG. 9 is a diagram for explaining the vector information and the concept of the shape holding area according to the second embodiment of the present invention. The vector information 100, 101, 102 is specified by the vector information input unit 207. For each vector information, in the coordinate system of the three-dimensional terrain data, for the vector information 100, an area 110 is a shape holding area. For the vector information 101, the area 111 is a shape holding area, and for the vector information 102, 112 is a shape holding area. Vertex data information included in these areas, which is displayed as a double circle in the figure, is determined to have a high degree of importance, and vertices are less likely to be omitted.
9 may be directly input from the vector information input unit 207 by the user.

  As described above, according to the second embodiment of the present invention, in the LOD control process in which the number of drawn polygons in a portion far from the viewpoint position is reduced by the terrain LOD control unit 205 according to the viewpoint position, vector information is added to the important terrain information. Using the shape holding area information obtained from the vector information input by the input unit 207, it is possible to save the important terrain structure and improve the display performance while displaying the highly accurate terrain data information. Moreover, since vector information different from the three-dimensional terrain data is used, it becomes easy to input important terrain information.

  The present invention is applied to various simulation devices such as flight simulators and driving simulators, display systems for disaster prevention monitoring, and computer game devices, so that the applied devices can display more realistic and accurate three-dimensional terrain display at high speed. It becomes possible to do.

It is a block diagram of the three-dimensional landform display apparatus in Embodiment 1 of this invention. It is explanatory drawing of the three-dimensional terrain data format in Embodiment 1 of this invention. It is explanatory drawing of the three-dimensional terrain data holding part in Embodiment 1 of this invention. It is explanatory drawing of the break line information in Embodiment 1 of this invention. It is explanatory drawing of the break line information holding part in Embodiment 1 of this invention. It is explanatory drawing of the example of vertex reduction used as the subject in Embodiment 1 of this invention. It is explanatory drawing of LOD control in Embodiment 1 of this invention. It is an example of a structure of the three-dimensional terrain display apparatus in Embodiment 2 of this invention. It is explanatory drawing of LOD control in Embodiment 2 of this invention.

Explanation of symbols

  200; Terrain data reading unit, 201; Terrain data holding unit, 202; Breakline information input unit, 203; Breakline information holding unit, 204; Scene control unit, 205; Terrain LOD control unit, 206; 207: Vector information input unit 208; Vector information holding unit 209: Shape holding region determination unit.

Claims (4)

  3D terrain data reading unit for reading 3D terrain data, 3D terrain data holding unit for holding the read 3D terrain data, and important for specifying important terrain structure parts from the stored 3D terrain data Projection on the screen, a terrain instruction means, an important terrain information holding unit that holds designated important terrain information, a scene control unit that controls the display scene projected on the screen according to the viewpoint position, line-of-sight direction, and angle of view The density of the 3D terrain data held by the 3D terrain data holding unit is controlled according to the size of the terrain LOD (Level Of Detail) control unit for generating polygons, and the polygon generated by the terrain LOD control unit A 3D terrain rendering unit that renders a 3D terrain using a computer graphics function, and the terrain LOD control unit is the viewpoint position determined by the scene control unit. 3D terrain characterized by generating polygons by selecting vertex data of 3D terrain data to be displayed and using the distance of the key and the important terrain information held in the important terrain information holding unit Data control unit.   Breakline information specified by the corresponding vertex group of the 3D terrain data is used as an important terrain structure part, and the important terrain instruction means is configured by the breakline information input unit for inputting the vertex group specifying the breakline information. The three-dimensional landform data control apparatus according to claim 1, wherein   The important terrain instruction means is composed of a vector information input unit for designating an important terrain structure part from vector information inputted separately from the three-dimensional terrain data, and the important terrain information holding part is designated as an important terrain structure part. A shape information area determination unit that increases the selection priority for vertices in the vicinity of the position in the three-dimensional space specified by the vector of the important terrain structure part. The three-dimensional terrain data control device according to claim 1, comprising:   An import process for reading 3D terrain data in the 3D terrain data reading unit, a holding process for holding the read 3D terrain data in the 3D terrain data holding unit, and an important terrain structure part from the held 3D terrain data Important terrain instruction process that specifies the important terrain information holding process that holds the specified important terrain information in the important terrain information holding part, and the display scene projected on the screen is controlled by the viewpoint position, line-of-sight direction, and angle of view Generated by a scene control process, a terrain LOD (Level Of Detail) control process that controls the density of 3D terrain data in the 3D terrain data holding unit that draws according to the size projected on the screen, and a terrain LOD control process A 3D terrain drawing process for drawing the polygons on the 3D terrain by a computer graphics function. In the terrain LOD control process, And the distance from the viewpoint position determined in step, by using the key terrain information stored in the key terrain information storage unit, three-dimensional topography data control method of generating a polygon that selects the vertex data drawing to be displayed.

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