JPH05290148A - Generating method and displaying method for topography model in artificial visual field generation - Google Patents

Abstract

PURPOSE:To generate no gap between adjacent triangles by dividing a triangle into two rectangular equilateral triangles when an approximation error is less than a permissible error and continuously dividing the triangle until the error becomes less than the permissible error. CONSTITUTION:The approximation error between the divided rectangular equilateral triangles concerns up to the rectangular equilateral triangle which is circumscribed with the respective sides of the triangles and includes the sides as its oblique side, and the approximation error of the triangle contacting those triangles is set below it, thereby modeling topography with an irreducible number of triangles. Further, errors are calculated as for slave nodes in order until an apparent angel error is not within a specific apparent angle permissible range, the approximation error of a triangle corresponding to a next slave node is obtained. Further, the size of the triangle is corrected corresponding to the difference between a specific apparent angel and the apparent angle of the triangle corresponding to the next slave node. Thus, when a view point moves away from the topography, a display is made without making any discontinuous variation in a process of variation in detail level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to generation of a simulated terrain model for generating a visual field using a computer and a method of displaying the generated terrain model.

[0002]

2. Description of the Related Art When a simulated visual field of a computer graphics is generated, an assumed three-dimensional scene is displayed on a screen as a two-dimensional image viewed from a designated viewpoint. There are, for example, the following three methods of creating a terrain model in a scene.

(A) Mountains and hills are approximated as a set of polyhedra (FIG. 9 (a)).

(B) The topography is approximated as a set of irregular triangles (FIG. 9 (b)).

(C) The terrain is approximated by a regular triangle having grid points as vertices (FIG. 9 (c)).

These polyhedrons and triangles are arranged along the surface of the terrain formed by mountains and hills for approximation.
At this time, as shown in FIG. 10, a predetermined position of the surface 101 formed by a polyhedron or a triangle, for example, the surface 1 of the terrain simulated as the center of gravity.
An interval 103 is generated between this and 02, and this is treated as an approximation error. At this time, the space 103 is taken with respect to the terrain surface 102 in the direction normal to the surface 101, but the space 104 may be taken when it is lowered from the surface 101 perpendicularly to the horizontal plane of the earth. A value obtained by dividing the approximation error by the distance 106 from the viewpoint 105 to the polyhedron or the triangle is defined as the view angle error.

[0007]

Each of the above approximation methods has the following drawbacks.

Regarding (a), the production efficiency is poor, it is difficult to optimize to a predetermined allowable error, and automatic leveling (to optimize to a predetermined allowable angle of view error) is difficult. There are drawbacks.

The method (b) has drawbacks such as difficulty in prioritization, difficulty in automatic leveling, and large amount of data.

Regarding (c), there are drawbacks such as many triangles and difficulty in automatic leveling.

When leveling is performed, a plurality of models having different degrees of detail are prepared in advance, and the models are switched according to the distance from the viewpoint. In that case,
There is a drawback that the image on the screen may change discontinuously due to a gap between the ridgelines of each polyhedron or triangle. As a method of avoiding discontinuous changes in the image, there is a method in which two adjacent models of detail are displayed at the same time and the transparency is changed continuously by mixing the two models. There is a drawback to making it larger.

The problem to be solved by the present invention is to provide a method of creating a terrain model and a method of displaying the terrain model, which solve the above-mentioned drawbacks.

[0013]

In order to solve the above-mentioned problems, the method of creating a terrain model of the present invention divides a given simulated coverage area of a square into two diagonal lines in the modeling of the terrain relating to the generation of the simulated visual field, The topography is approximated by two right-angled isosceles triangles, and the approximation error e of each right-angled isosceles triangle
Let ε0 be the maximum distance from the triangle to the topographic surface, and let ε1, ε2, and ε3 be the circumscribed triangle errors of an isosceles right triangle circumscribing each side of the triangle and using that side as the hypotenuse (circumscribing triangle The error εi is the maximum distance εi0 from the triangle to the topographic surface, and the circumscribed triangle errors εi1 and εi2 of the isosceles triangle that circumscribes the sides that sandwich the right angle of the triangle.
The maximum value of), the maximum value of ε0, ε1, ε2 and ε3, and if the approximation error e when approximating the terrain with the triangle is within the specified tolerance, the triangle division is terminated. However, if the approximation error e is not within the allowable error, the triangle is divided into two right-angled isosceles triangles and the divided triangles are divided until the approximation error e is within the allowable error.

Further, in the method of displaying the terrain model, the approximation error of each right-angled isosceles triangle relating to the terrain model created above is made to correspond to the node of the binary tree by division, and the assumed viewpoint in the simulated field of view is set. On the other hand, starting from the root of the binary tree, its child nodes are sequentially obtained from the child nodes closer to the viewpoint, and the angle of view error is defined as the approximation error divided by the distance from the viewpoint to the triangle.
The view angle error is sequentially calculated for the child nodes until the view angle error is within a predetermined view angle allowable error, and the simulated view generation display processing is performed using the terrain data of the triangle at that time.

In the above method of displaying the terrain model, when the view angle error is not within the predetermined view angle allowable error, the approximation error of the triangle corresponding to the next child node is obtained and the predetermined view angle and the next child are obtained. The vertices of the triangle corresponding to the child node may be corrected and displayed according to the difference from the angle of view of the triangle corresponding to the node.

[0016]

In the method of creating a terrain model configured as described above, the approximation error of the divided right-angled isosceles triangle is circumscribed not only on the triangle itself but also on each side of the triangle and the side is defined as a hypotenuse. It recursively targets up to those in the isosceles right triangle, and the approximation error of the triangles tangent to them is guaranteed to be less than them, and the terrain is modeled with the minimum number of triangles within the allowable error.

Further, in the method of displaying the terrain model, the view angle error is sequentially calculated for the child nodes until the view angle error is within the predetermined view angle allowable error, and no gap is generated between the triangles.

Further, when the view angle error is not within the predetermined view angle allowable error, the approximation error of the triangle corresponding to the next child node is obtained and the view angle of the triangle corresponding to the predetermined view angle and the next child node is obtained. The size of the triangle corresponding to the child node is corrected according to the difference between and, and it is displayed without causing discontinuous changes in the process of changing the level of detail when the viewpoint approaches the topography.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1A is a flowchart of a process of generating a terrain model. A given square modeling area or a block (simulated coverage area) obtained by dividing it into a lattice shape is divided into two by diagonal lines, and the terrain is approximated by two right-angled isosceles triangles. Step P11 is a step of calculating an approximation error of the given triangle (FIG. 2) with respect to the terrain,
The maximum value of the approximation error of the triangle sharing the hypotenuse is defined as the approximation error e of the triangle. Step P12 is the approximation error e
Is written in the corresponding node (indicated by a circle in FIG. 2), step P13 evaluates the approximation error e and ends the process for that node if it is within the tolerance, step P14 allows the approximation error e If it is not within the error, the step of dividing the triangle into two, step P15, recursively processes one of the two child triangles formed by the division, for example, the left child triangle, that is, step P11 to step P13 or The step P14 represents a step of performing the same processing as step P14, and the step P16 represents a step of recursively processing the right child triangle, for example. Here, the triangle has its apex rotated counterclockwise, and only the hypotenuse thereof is noted and represented by an isosceles right triangle. For example, the triangle in FIG.
1, R2), the left child triangle that is a split of the left child triangle is (RR, R1), and the right child triangle is (R2, R2).
R). Therefore, e (R1, R2) is the approximation error of the parent triangle (R1, R2) before division in FIG.
(R2, R1) is an approximation error of the other right-angled isosceles triangle that forms a pair with the triangle (R1, R2) formed when the square is divided into two by diagonal lines.

The approximation error of each right-angled isosceles triangle is the distance (error) e1 between its own surface and the topographic surface approximated, and each side circumscribing each side sandwiching the right angle of the triangle and making that side a hypotenuse. It is defined as the maximum value among the respective errors e2 and e3 of the isosceles right triangle. The approximation error of the isosceles right triangle is defined as the maximum value of the approximation errors of the two isosceles triangles sharing the hypotenuse.

FIG. 1B is a flow chart for calculating the approximation error of each triangle for the approximation error calculation of step P11 in FIG. 1A. In the figure, step P
Step 20 is a step of determining whether the triangle is a terminal triangle, or if it is not a terminal triangle, go to Step P21,
Step P21 is a step of calculating an approximation error e1 between the terrain directly covered by the triangle and the triangle, and Step P22.
Is a step of calculating an approximation error e2 of a triangle circumscribing one side of a right angle of the triangle and a group of triangles circumscribing the triangle, and step P23 is tangent to a triangle circumscribing the other side of the triangle intersecting the right side of the triangle. The step of calculating the approximation error e3 of a group of triangles, step P24 represents the step of setting the maximum value of e1, e2, e3 calculated in steps P21 to P23 as the approximation error of the triangle. Step 25 is a step of setting the error to 0 when the triangle is at the end. FIG. 2B shows a set of triangles for evaluating the error when the target triangles are R1, R2, and R3. These calculations are performed off-line in advance before the operation of generating the simulated visual field of the computer graphic and stored in the memory.

FIG. 3 is an example of a plan view display when the terrain is displayed using the above terrain model.
The four blocks of BCFE, DEHG, and EFIH are displayed using the isosceles right triangle divided as described above.

FIG. 4 is a binary tree of the terrain model generated by the processing according to the terrain model generation flowchart. In FIG. 4A, the node N1 is a root node, and is a square area ABCD to be modeled (see FIG.
(B)), the node N2 is the area ABC by the diagonal line AC.
Of the right-angled isosceles triangles formed by dividing D into two, the left triangle ACD and the node N3 represent the right triangle of the diagonal line AC.

In the following, as shown in FIG. 4 (c), the node Ni generally represents an isosceles right triangle (R1, R2) (FIG. 4 (d)), and the node Ni + 1 is a triangle formed by a perpendicular line drawn from RR to R1R2. Left triangle (RR, R1) of right-angled triangles formed by dividing (R1, R2) into two
The note Ni + 2 represents the right triangle (R2, RR).

The error attached to each node represents the error when the triangle represented by the node and the group of triangles in contact with the sides of the triangle approximate the terrain.

FIG. 5 is a flowchart showing the processing for displaying the terrain model. In the figure, step P31 is a step of calculating the view angle error of a given triangle. Here, the view angle error is defined as a value obtained by dividing the approximation error by the distance r from the viewpoint to the triangle. Step P32 is a step of evaluating the view angle error. The view angle error is calculated by the fact that when the viewpoint moves in the assumed space, the degree of detail of the terrain surface that can be observed from the viewpoint should change in inverse proportion to the distance r from the viewpoint to the triangle. This is because it is for determining whether the view angle from the position, that is, the size of the displayed triangle is suitable for the error of the triangle. Step P33 is a step of displaying a triangle when the view angle error is within the allowable error, and Step P34 is whether the distance r to the triangle is within the transition zone (FIG. 6) when the view angle error is not within the allowable error. This is a determination step. The transition zone is an area within the range of βRth ≦ r <Rth in FIG. However, Rth is a threshold distance,

Rth = e (R1, R2) / δ

Where e (R1, R2) is the approximation error of the triangle, and δ is the allowable viewing angle error. Step P35 is a step of correcting the triangle according to the equation (1) when it is within the transition zone. That is,

[0029]

[Equation 1]

It is For example, << Ri >> represents a three-dimensional vector, and points on the ground surface << Ri >> = (x _i , y _i ,
z _i ). In addition, in this specification, the vector notation is used in combination with the case where it is << and the case where it is thick. << r _i >> represents a two-dimensional vector, and points on the ground surface are projected perpendicularly to the horizontal plane, << r _i >> = (x _i , y _i ).
Is. h (<< r _i >>) is the altitude at the position r _i (<< r _i >>), and h (<< r _i >>) = zi. This correction is performed to prevent discontinuity in switching the detail level of the terrain surface because the view angle is not within the allowable error in step P34 in the transition zone. Correction rate α (0 <α <1; α = (r−βRth) according to the distance r to the triangle
/ (Rth-βRth)) is defined. The state of this correction is shown in the perspective views of FIGS. FIG. 7A shows a parent triangle, and FIG. 7B shows a child triangle. The correction rate α is larger as the distance r from the viewpoint to the triangle is larger in the transition zone. While it is in, even if the detail level is switched, it keeps approaching the parent triangle for a while and the discontinuous change of the terrain is not felt.

Step P36 is a step of determining which side of the viewpoint is the child triangle formed by dividing the triangle into two equal parts, and step P37 is the step where the viewpoint is the left child note (triangle).
Recursively processing the left child node if it is on the side,
Step P38 is a step of recursively processing the right child node after step P37 when the viewpoint is also on the left child node side, and step 39 is recursing the right child node when the viewpoint is on the right child node side. Process, step 3
Reference numeral 10 denotes a step of recursively processing the left child node subsequent to step P39 when the viewpoint is also on the right child node side.

FIG. 8 is a block diagram of an apparatus used in the above method. In this device, a visual object is numerically modeled and simulated as a combination of polygons, polygonal surfaces (polygons) and light spots. In FIG. 8, the field-of-view calculation device 81 stores information such as the positions of all the visual objects included in the assumed three-dimensional scene, the positions of the vertices forming the surface, and the color. For example, in the case of an airplane simulator, a visual object within the field of view is selected according to the viewpoint information such as the direction and height of the airplane, the viewpoint position of the pilot, and the like, and is sent to the geometric calculation device described later and the coordinates used by the geometric calculation device. Calculate the matrix for conversion. Further, the database generation device 811 creates a database off-line, that is, creates the data of the terrain model created by the above method and stores it in the memory 812. The terrain model data is read from the memory in order to respond to the terrain change due to the change of the viewpoint.

The geometrical calculation device 82 gives priority to the visual objects sent from the visual field calculation device 81 in the order closer to the visual point according to the positional relationship with the visual point. Calculation of perspective view of the visual object from a specified viewpoint, brightness of each surface when illuminated by a specified light source, calculation of haze, perspective projection of polyhedron edge defining visual object Geometric calculation such as calculation as to whether or not the line (edge) on the figure represents the outline of the visual object is performed. Further, coordinate conversion, perspective conversion, calculation of intersection brightness, and the like regarding the light spot are performed, and the result is output together with the priority order to a video signal generator described later.
Also, parameters such as coordinate conversion for mapping the texture pattern to polygons are calculated and transferred to the video signal generation circuit. Further, the geometric calculation device 82
The terrain data read from the visual field calculation device 81 is judged whether the triangle has a predetermined allowable error, and if it is within the allowable error and further correction is necessary, the correction is performed by the above method.

The video signal generator 83 is a geometric calculator 8
The position of the intersection of the scanning line and the edge, the brightness and the degree of haze (fade) at the intersection, based on the signal output from 2
Brightness and fade calculations and hidden surface removal are performed to generate a video signal, which is displayed on the display device 84 in color.

[0035]

As described above, according to the present invention, it is assured that two right-angled isosceles triangles sharing a hypotenuse have the same approximation error, and the approximation error of a triangle tangent thereto is less than that. Therefore, there is no gap between adjacent triangles. Further, since the triangle is recursively divided while evaluating the error, it is possible to model the terrain with the minimum number of triangles within the allowable error.

Further, the approximation error calculated as described above is written in each node of the binary tree, and the triangle is divided so that the value obtained by dividing the approximation error by the distance from the viewpoint is equal to or less than the allowable viewing angle error. Since it is displayed, the terrain can be model-displayed with the minimum number of triangles.

When the viewpoint moves away from or approaches the triangle and the level of detail changes, the detail level is switched and is kept close to the parent triangle for a while, so that discontinuous change in the terrain is not felt.

Further, the calculation amount is small because only one model is displayed, not the method of displaying two models having different details in a mixed manner.

Further, as described above, the triangulation is performed by recursively dividing the triangulation into two by a straight line, so that it is easy to prioritize the concealment of the triangle, and the hidden surface can be easily erased. Further, as described above, since the process of creating and displaying the terrain model is simple, it is suitable for automatic creation of the terrain model by a computer and real-time display.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention, which is a flowchart of a process for generating a terrain model, a diagram illustrating a given triangle, and a flowchart for calculating an approximation error of the triangle.

FIG. 2 is a diagram illustrating a given triangle.

FIG. 3 is an example of a plan view displayed using the generated terrain model.

FIG. 4 is a binary tree of a terrain model generated by processing according to a terrain model generation flowchart.

FIG. 5 is a flowchart showing a process of displaying a terrain model.

FIG. 6 is a diagram illustrating a transition zone.

FIG. 7 is a perspective view illustrating correction in a transition zone. The figure (a) shows a parent triangle, and the figure (b) shows a child triangle.

FIG. 8 is a block diagram of an apparatus used in the method of the present invention.

FIG. 9 is a diagram illustrating the creation of a conventional terrain model.

FIG. 10 is a diagram illustrating an approximation error and a perspective angle error.

[Explanation of symbols]

 81 Visibility calculation device 82 Geometric calculation device 83 Video signal generation device 84 Display device

Claims (3)

[Claims] 1. In modeling of terrain related to generation of simulated visual field, a given simulated coverage area of a square is divided into two by diagonal lines, terrain is approximated by two right-angled isosceles triangles, and an approximation error e of each right-angled isosceles triangle. Let ε0 be the maximum distance from the triangle to the topographic surface, and let ε1, ε2, and ε3 be the circumscribed triangle errors of an isosceles right triangle circumscribing each side of the triangle and using that side as the hypotenuse (circumscribing triangle Error εi
Is the maximum value of the maximum distance εi0 from the triangle to the topographical surface and the circumscribed triangle errors εi1 and εi2 of the isosceles triangle circumscribing the sides of the triangle at right angles), ε0,
Set the maximum value of ε1, ε2, and ε3, and if the approximation error e when approximating the terrain with the triangle is within the specified tolerance, the triangle division is terminated and the approximation error e must be within the tolerance. For example, a method of creating a terrain model in the generation of a simulated visual field, characterized in that the triangle is divided into two right-angled isosceles triangles and the triangles after the division are divided until an approximate error e falls within an allowable error. 2. In modeling of terrain concerning generation of simulated visual field, a given simulated coverage area of a square is divided into two by diagonal lines, terrain is approximated by two right-angled isosceles triangles, and an approximation error e of each right-angled isosceles triangle. Let ε0 be the maximum distance from the triangle to the topographic surface, and let ε1, ε2, and ε3 be the circumscribed triangle errors of an isosceles right triangle circumscribing each side of the triangle and using that side as the hypotenuse (circumscribing triangle Error εi
Is the maximum value of the maximum distance εi0 from the triangle to the topographical surface and the circumscribed triangle errors εi1 and εi2 of the isosceles triangle circumscribing the sides of the triangle at right angles), ε0,
Set the maximum value of ε1, ε2, and ε3, and if the approximation error e when approximating the terrain with the triangle is within the specified tolerance, the triangle division is terminated and the approximation error e must be within the tolerance. For example, the triangle is divided into two right-angled isosceles triangles, and the triangles after the division are divided until the approximation error e falls within a permissible error. For the hypothesized viewpoint in the simulated field of view, start from the root of the binary tree and obtain the approximation error in order from the child node closer to the viewpoint, The value is divided by the distance from the viewpoint to the triangle, and the angle-of-view error is calculated for each child node in sequence until the angle-of-view error is within the specified angle-of-view tolerance. Display method of terrain models in simulated vision generation, characterized by simulated vision generation display process using the chromatography data. 3. In modeling of a terrain related to generation of a simulated visual field, a given simulated coverage area of a square is divided into two by diagonal lines, and the terrain is approximated by two right isosceles triangles, and an approximation error e of each right isosceles triangle. Let ε0 be the maximum distance from the triangle to the topographic surface, and let ε1, ε2, and ε3 be the circumscribed triangle errors of an isosceles right triangle circumscribing each side of the triangle and using that side as the hypotenuse (circumscribing triangle Error εi
Is the maximum value of the maximum distance εi0 from the triangle to the topographical surface and the circumscribed triangle errors εi1 and εi2 of the isosceles triangle circumscribing the sides of the triangle at right angles), ε0,
Set the maximum value of ε1, ε2, and ε3, and if the approximation error e when approximating the terrain with the triangle is within the specified tolerance, the triangle division is terminated and the approximation error e must be within the tolerance. For example, the triangle is divided into two right-angled isosceles triangles, and the triangles after the division are divided until the approximation error e falls within a permissible error. For the hypothesized viewpoint in the simulated field of view, start from the root of the binary tree and obtain the approximation error in order from the child node closer to the viewpoint, The value is divided by the distance from the viewpoint to the triangle, and the angle-of-view error is calculated for each child node in sequence until the angle-of-view error is within the specified angle-of-view tolerance. In addition to performing a simulated visual field generation display process using the data, when the view angle error is not within the predetermined view angle allowable error, an approximate error of the triangle corresponding to the next child node is obtained and the predetermined view angle and the next child are obtained. A method for displaying a terrain model in simulated visual field generation, which comprises correcting and displaying the vertices of the triangle corresponding to the child node according to the difference from the angle of view of the triangle corresponding to the node.