JP3270535B2 - How to create and display terrain models including objects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modeling a state in which a three-dimensional object is arranged on the ground surface in computer graphics and a method for displaying the state.

[0002]

2. Description of the Related Art In computer graphics, it is very important to delete a portion of an object image that is hidden by a nearer object. As representative methods of this processing, a depth buffer method and a BSP (binary
space partitioning) method.

In the depth buffer method, the color and depth of an object image are calculated for each pixel, and written in a frame buffer. When a new object image is calculated, the depth is also calculated and the object image is already written in the frame buffer. If the depth is smaller than the current depth value, the color and depth value of the frame buffer are rewritten to the value of the new object.

[0004] In the BSP method, a space is recursively divided into two parts, represented by a binary tree, and images are calculated in order from an object located in a space close to the viewpoint and written into a frame buffer. At this time, if a video has already been written, a new video is not calculated.

[0005]

As described above, the depth buffer method and the BSP method have the following drawbacks.

The depth buffer method requires a large amount of calculation because the depth of each pixel is calculated and compared. If the depth value is large, the calculated video and depth value are wasted.

Although the BSP method requires a small amount of calculation and can perform high-speed drawing, it has disadvantages such as the need to shift the separate plane or divide the object when the separate plane that divides the space crosses the object. In particular, when the object is a moving object, it is necessary to perform the above processing online.

An object of the present invention is to provide a method of creating and displaying a terrain model that realizes concealment processing with improved processing efficiency.

[0009]

A method for creating and displaying a terrain model including an object to solve the above-mentioned problem is described in a terrain modeling relating to generation of a simulated view using a computer. The area is divided into two by a diagonal line, the terrain simulated by two right-angled isosceles triangles is approximated, and the approximation error e between each right-angled isosceles triangle and the simulated terrain surface is calculated from the triangle to the simulated terrain surface. Is the maximum distance of δ, and the circumscribed triangle errors of a right-angled isosceles triangle circumscribing each side of the triangle and the hypotenuse are ε1, ε2, and ε3, respectively (the circumscribed triangle error εi Δ1, ε1, ε2, the maximum distance to the surface δi and the circumscribed triangle errors εi1 and εi2 of the isosceles triangle circumscribing the sides of the triangle.
If the approximation error e when approximating the terrain simulated by the triangle is within the specified tolerance, the division of the triangle 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 divided triangles are divided until the approximation error e is within an allowable error, thereby generating terrain model data. In relation to the object above the terrain surface, if the object is completely contained within the triangle, write a pointer to the object in the triangle, and if there are multiple objects above the triangle, Connect the objects with a chain or divide the triangle further so that one triangle contains only one object and write a pointer to the object in the triangle, and If you are across the square,
A pointer pointing to the object is written in all the triangles on which the object is hung, a flag indicating whether or not the object has been displayed is prepared, and the approximation error of each of the divided right-angled isosceles triangles is divided into two. For a hypothetical viewpoint in the simulated field of view, an approximation error is obtained for the assumed viewpoint in the simulated field of view, starting from the root of the binary tree and descending from the child node closer to the viewpoint in order. Is the value obtained by dividing the approximation error by the distance from the viewpoint to the triangle, and successively calculating the prospective angle error for the child nodes until the prospective angle error is within a predetermined prospective angle tolerance, and within the tolerance. When performing a simulated view generation and display process using the terrain data for a triangle, when an object is present on the terminal triangle and the displayed flag is reset, It sets the display flag to display the body, after displaying all objects in a triangle, in which so as to display the triangle.

[0010]

[Function] The approximation error of the divided right-angled isosceles triangle is recursively targeted not only for the triangle itself but also for a right-angled isosceles triangle that circumscribes each side of the triangle and sets the side as the hypotenuse. The approximation error of the triangles in contact with them is guaranteed to be less than them, and the terrain is modeled with the minimum number of triangles within the tolerance.

[0011] It is checked which triangle the object on the terrain is on, and the following processing is performed according to the positional relationship between the triangle and the object.

(A) When the object is completely contained inside the triangle: A pointer to the object is written in the triangle, and the triangle is associated with the object. If there are multiple objects in the triangle, connect all the objects with a chain, or divide the triangle further so that one triangle contains only one object, and then Write.

(B) When the object straddles two or more triangles: A pointer pointing to the object is written in all the triangles on which the object spans.

Further, when displaying a triangle, an approximation error of the divided triangle is made to correspond to a node of the binary tree obtained by the division. The approximation error is obtained in order from the node closer to the viewpoint, and the calculation of the prospective angle error is sequentially performed on the child nodes until the prospective angle error falls within a predetermined prospective angle allowable error. A triangle closest to the viewpoint within a predetermined permissible angle tolerance is selected and displayed from a node closer to the viewpoint. The object has a flag indicating whether it has been displayed or not, and if the object exists on the triangle, the displayed flag of the object is checked first, and if the flag is reset, the object is displayed, Set the displayed flag and display the triangle. When a plurality of objects exist on one triangle, the objects are displayed in order from the one closer to the viewpoint.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 4A is a flowchart of a process for generating a terrain model. A given square modeling area or a block (simulated coverage area) obtained by dividing the modeling area into a grid is divided into two parts 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. 5) 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 into a corresponding node (indicated by a circle in FIG. 5), a step P13 evaluates the approximation error e, and if the error is within an allowable error, the process for the node is terminated. If the error is not within the error, a step of dividing the triangle into two, step P15 is to recursively process one of the two child triangles formed by the division, for example, the left child triangle, that is, step P11 to step P13 or , And step P16 represents a step of recursively processing, for example, the right child triangle. Here, it is assumed that the triangle turns its vertex in a counterclockwise direction, and that only its hypotenuse is described to represent a right-angled isosceles triangle. For example, the triangle in FIG.
1, R2), and the left child triangle obtained by dividing it is (RR, R1), and the right child triangle is (R2, R2).
R). Therefore, ep (R1, R2) refers to the partial error ε of the parent triangle (R1, R2) before division in FIG. 5, and ep (R2, R1) refers to the triangle (R1) formed when the square is divided into two diagonal lines. , R2) is the partial error ε of the other right-angled isosceles triangle.

The partial error of each right-angled isosceles triangle is the distance (error) δ between its own surface and the approximated terrain surface, and It is defined as the maximum value among the partial errors ε1, ε2 of the right-angled isosceles triangle. The approximation error of the right-angled isosceles triangle is defined as the maximum value of the partial errors of the two right-angled isosceles triangles sharing the hypotenuse.

FIG. 4B is a flowchart for calculating the approximate error of each triangle for calculating the approximate error in step P11 in FIG. 4A. In the figure, step P
20 is a step of judging whether or not the triangle is a terminal triangle, and if not, 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 the triangle at a right angle and a group of triangles circumscribing the triangle. Step P23 is in contact with a triangle circumscribing the other side of the triangle at a right angle. A step of calculating an approximation error e3 of a group of triangles, and step P24 represents a step of setting the maximum value of e1, e2, and e3 calculated in steps P21 to P23 as an approximation error of the triangle. Step P25 is a step of setting the error when the triangle is at the end to 0. FIG. 5B shows a set of triangles for evaluating an error when the target triangle is R1, R2, and R3. These calculations are performed in advance off-line before operation of generating a simulated view of computer graphics, and stored in a memory.

FIG. 6 shows a binary tree of the terrain model generated by the processing according to the terrain model generation flowchart. In FIG. 6A, a node N1 is a root node, and a square area ABCD to be modeled (FIG.
(B)), the node N2 is connected to the area ABC by a 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.

Hereinafter, as shown in FIG. 6C, the node Ni generally represents a right-angled isosceles triangle (R1, R2) (FIG. 6D), and the node Ni + 1 is formed by a perpendicular drawn from RR to R1R2. Left triangle (RR, R1) among right-angled triangles formed by dividing (R1, R2) into two
And the note @ Ni + 2 represents the right triangle (R2, RR).

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

FIG. 7 is a flowchart showing a process for displaying a terrain model. In the figure, step P31 is a step of calculating a prospective angle error of a given triangle. Here, the estimated 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 estimated angle error. The reason for calculating the perspective angle error is that when the viewpoint in the assumed space moves, the approximation error 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. Because. Step P33 is a step of displaying a triangle when the estimated angle error is within the allowable error.
34 is a step of determining whether or not the distance r to the triangle is within the transition zone (FIG. 8) when the expected angle error is not within the allowable error. The transition zone is denoted by β in FIG.
It is an area in the range of Rth ≦ r <Rth. Where R
th is the threshold distance,

Rth = e (R1, R2) / θ

Where e (R1, R2) is the approximation error of the triangle and θ is the allowable expected angle error. Step P35 is a step of correcting the triangle in accordance with the equation (1) when it is within the transition zone. That is,

[0024]

(Equation 1)

## EQU1 ## For example, "Ri" represents the three-dimensional vector, a point on the ground _{"Ri" = (x i,} y i,
z _i ). Note that, in this specification, vector notation is used in both cases where <<>> is used and when it is thick. "R _i" represents a two-dimensional vector, a point obtained by projecting perpendicularly the point on the earth's surface to the horizontal _{surface, "r i" = (x} i, y i)
It is. h ( "r _i") is an elevation in the position _{r i ( "r i")} , h ( "r i") is a = zi. This correction is performed in order to prevent discontinuity when switching the degree of detail of the terrain surface because the estimated 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 distance r to triangle
/ (Rth-βRth)) is defined. The state of this correction is shown in the perspective views of FIGS. 9 (a) and 9 (b). FIG. 9A shows a parent triangle, and FIG. 9B shows a child triangle. The correction rate α is larger as the distance r from the viewpoint to the triangle in the transition zone is larger, so for a while after the viewpoint is closer to the triangle and within the threshold distance Rth, that is, in the transition zone, While in, even if the degree of detail is switched, it is close to the parent triangle for a while and does not feel discontinuous change in terrain.

Step P36 is a step of determining which side is the viewpoint among the child triangles obtained by bisecting the triangle. Step P37 is a step of determining whether the viewpoint is on the left child node (triangle) side. Step P38 is a step of recursively processing the right child node following step P37 if the viewpoint is also on the left child node side, and step P39 is a viewpoint being on the right child node side. In this case, the step of recursively processing the right child node, step P310 shows the step of recursively processing the left child node following step P39 when the viewpoint is also on the right child node side.

According to the present invention, in the above-described method for creating and displaying a terrain model, a state in which an object is arranged on the ground surface is modeled and displayed. FIG. 1A is a plan view illustrating the state of a modeled terrain and an object, and FIG. 1B is a data structure diagram for modeling the terrain including the object. The binary tree representing the terrain is generated as described above. In FIG.
Squares U, V, W, and X represent objects, and a plurality of objects U,
V is included in the same triangle DAE, a pointer of the object U is written in a node corresponding to the triangle DAE, and the object V is connected to the object U by a chain. The case where the object W is completely included inside the triangle CDE is shown, and the object W is connected by a pointer. Further, the object X extends over two triangles, the triangle CEG and the triangle GEH, and a pointer pointing to the object X is written in both triangles. It should be noted that a flag is provided for an object that spans a plurality of triangles, indicating whether the object has already been displayed.

FIG. 2 is a processing flow for associating an object with a triangle representing the terrain by a pointer, that is, a processing flow for arranging an object in a triangle terrain model obtained by the above-described division. A routine called "allocate" processes nodes recursively with information on an object (obj).
obj is information indicating the position and size of the object, node
Is information representing a node of the terrain model. S (1) is a step for checking whether a node represents a terminal triangle, S
(2) a step of linking the triangle and the object by a pointer when the node is a terminal triangle, and a step of checking whether the object is on the left or right triangle when the node is not the terminal triangle, S (3) (4) processing the left node if the object is completely on the left triangle; S (5) processing the right node if the object is completely on the right triangle; S (6) ), S (7) represent the steps of processing both nodes when the object straddles the left and right triangles.

FIG. 3 is a processing flow for displaying the terrain including the object shown in FIG. Process nodes recursively,
When the terminal triangle is reached, the objects on which the displayed flag is not set are displayed in order from the viewpoint closest to the viewpoint, and the triangle is processed after the displayed flag is set. T (1) is a step of checking whether the node is a terminal triangle or a node representing a triangle having a sufficiently small angle error. If the node is a triangle representing a terminal, T (2) finds an object existing on the triangle. T (3) is a step of examining the displayed flag of the object and displaying an object for which the flag is not set;
(4) setting a displayed flag, T (5) displaying a triangle, T (6) checking if the viewpoint is on the left or right triangle if the node is not the terminal triangle, T (7) is a step of processing the left node when the viewpoint is on the left triangle, and T (8) is a step of processing the right node when the viewpoint is on the right triangle.

FIG. 10 is a block diagram of an apparatus used in the above method. In this device, a visual object is simulated by numerical modeling as a combination of a polygon, a polygonal surface (polygon), and a light spot. In FIG. 10, the visibility calculation device 101
Stores information such as the positions of all visual objects included in the assumed three-dimensional scene, the positions of vertices constituting a surface, colors, and the like. For example, in the case of an airplane simulator, a visual object in the field of view is selected according to viewpoint information such as the direction, height of the airplane, and the viewpoint position of a pilot, and is sent to a geometry calculation device described later, and coordinates used by the geometry calculation device are used. Calculate matrix for conversion. In addition, a database is created offline by the database generation apparatus 1011, that is, data of the terrain model and the three-dimensional object created by the above method are created and stored in the memory 1012. The terrain model data and the object data are read from the memory in order to cope with the change of the terrain and the appearance of the object due to the change of the viewpoint.

The geometric calculator 102 is a view calculator 101
Priorities are assigned to the visual objects sent from the order from the viewpoint in accordance with the positional relationship with the viewpoint. Geometric calculations such as calculation of a perspective view of the visual object from a specified viewpoint, calculation of the brightness of each surface when illuminated by a specified light source, and calculation of haze are performed. Further, coordinate conversion, perspective conversion, intersection luminance calculation, and the like for the light point are performed, and the result is output to a video signal generator described later together with the priority. Also, parameters such as coordinate transformation for mapping the texture pattern to the polygon are calculated and transferred to the video signal generation circuit. Further, the geometric calculation device 10
2 judges whether the triangle of the terrain data read from the visibility calculation device 101 has a predetermined allowable error, and if the triangle is within the allowable error and further correction is necessary, the correction is performed by the above method.

The video signal generator 103 calculates the position of the intersection of the scanning line and the edge, the brightness and haze (fade) at the intersection, the calculation of the brightness and fade, and the hidden based on the signal output from the geometric calculator 102. The surface is erased, a video signal is generated, and the video signal is displayed on the display device 104 in color.

[0033]

As described above, according to the present invention, BS
In the P method, priorities can be assigned to properties on a separate plane, and calculation and comparison of the depth for each pixel are not required, and processing efficiency is significantly improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a data structure for modeling a terrain including an object.

FIG. 2 is a diagram illustrating a processing flow for associating an object with a terrain model.

FIG. 3 is a diagram showing a processing flow for displaying a terrain including the object shown in FIG. 1;

FIG. 4 is a flowchart of processing for generating a terrain model,
FIG. 4 is a diagram illustrating a given triangle and a flowchart illustrating an approximation error of the triangle.

FIG. 5 is a diagram illustrating a given triangle.

FIG. 6 is a binary tree of a terrain model generated by a process according to a terrain model generation flowchart.

FIG. 7 is a flowchart illustrating a process of displaying a terrain model.

FIG. 8 is a diagram illustrating a transition zone.

FIG. 9 is a perspective view illustrating correction in a transition zone. FIG. 3A shows a parent triangle, and FIG. 3B shows a child triangle.

FIG. 10 is a block diagram of an apparatus used in the method of the present invention.

[Explanation of symbols]

 Reference Signs List 101 View calculation device 102 Geometric calculation device 103 Video signal generation device 104 Display device

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-75682 (JP, A) JP-A-4-500878 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G06T 17/50 G06T 15/00 JICST file (JOIS)

Claims (1)

(57) [Claims] In the modeling of terrain relating to the generation of a simulated field of view using a computer , (a) a simulated area covered by a square is divided into two by a diagonal line, and the terrain simulated by two right-angled isosceles triangles is approximated. Approximate error e between each right-angled isosceles triangle and the terrain surface to be simulated is defined as the maximum distance from the triangle to the simulated terrain surface as δ, a right angle circumscribing each side of the triangle and defining that side as the hypotenuse. Let the partial errors of the isosceles triangle be ε1 and ε, respectively.
2, ε3 (partial error εi of a right-angled isosceles triangle
Is the maximum value of the maximum distance δi from the triangle to the terrain surface and the partial errors εi1 and εi2 of the isosceles triangle circumscribing the right and left sides of the triangle), δ, ε1, ε2
If the approximation error e when approximating the shape simulated by the triangle is within the specified tolerance, the division of the triangle is terminated, and the approximation error e becomes data of terrain model by splitting the triangles after if not within tolerance divides the triangle into two right-angled isosceles triangle divided up approximation error e is within the tolerance
Generate, (b) in relation to the triangle to be approximated to the simulated view viewpoint terrain surface above the object as seen in, (b1-1) if the object is completely contained in the interior of the triangle, the object to triangles (B1-2) When there are a plurality of objects above the triangle, all the objects are connected by a chain, or the triangle is further divided to form one object in one triangle. (B2) If the object straddles two or more triangles, write a pointer pointing to the object in all the triangles on which the object is placed, and The object is provided with a flag indicating whether or not the object has been displayed. (C) The approximation error of each of the divided right-angled isosceles triangles is made to correspond to the node of the binary tree obtained by the division. For the viewpoint to be determined, starting from the root of the binary tree, obtain the approximation error of the child nodes in order from the child node closer to the viewpoint, and divide the expected angle error by the approximation error divided by the distance from the viewpoint to the triangle. When calculating the prospective angle error for the child nodes sequentially until the prospective angle error falls within the predetermined prospective angle allowable error, and performing the simulated view generation display process using the terrain data for the terminal triangle, the terminal When the object is present on the triangle and the displayed flag is reset, the objects are displayed in order from the viewpoint closest to the viewpoint, after displaying all the objects within the triangle, the displayed flag is set, and the triangle is displayed. A method for creating and displaying a terrain model including an object characterized by the following .