CN109410332B - Three-dimensional space geometric virtual model detail level cutting method based on point, line and surface - Google Patents

Abstract

The invention discloses a method for cutting a three-dimensional space geometric virtual model based on a point line surface. Firstly, separating the attribute of a three-dimensional space geometric virtual model from an integral structure, searching the structures of vertexes, lines and surfaces with shared properties in the model, sharing positions to texture, marking the vertexes in data processing, and acquiring adjacent triangular mesh information of the model through surrounding triangles neighboring the vertexes after the vertexes finish mapping processing of the associated triangles; and calculating each weight index by means of model global grid information to obtain the importance of the point-line surface of the region in the global grid model. The less important regions are deleted or simplified and the more important regions are retained. The method can limit the layer times and complexity of cutting, namely, the visual observation effect is not influenced, meanwhile, the system can be ensured to normally carry out the model construction function, and the effectiveness and the stability of the model rendering process are considered.

Description

Level-of-detail clipping method of three-dimensional geometric virtual model based on point, line and surface

technical field

The invention belongs to the technical field of three-dimensional space modeling, and more specifically relates to a level-of-detail cutting method of a three-dimensional space geometric virtual model based on points, lines and planes.

Background technique

3D space model rendering is not to design exactly the same on the machine from the inside to the outside according to the entity itself. Generally speaking, we design the same-shaped wireframe of the object, and attach texture, material and texture on its surface, whether it is Color, lighting or pattern are all expressed on the model in this way. Textures, materials, and maps are essentially the same as pictures, but they are designed specifically for 3D models, where pixels can be projected onto pixels in screen space, making it as realistic as pasting an image onto it.

From the moment the 3D modeling technology was born, the problem of how to draw and render faster has followed. From the efficient calculation of the central processing unit (Central Processing Unit, CPU) and graphics processing unit (Graphics Processing Unit, GPU) of the underlying hardware, to the graphics rendering algorithm of the middle-level graphics program, to the various rendering technologies of the top-level application software, there are extremely Large space for performance optimization can be adapted to different computer configurations, different rendering algorithms, and different scene rendering.

In addition to the above-mentioned vertical optimization factors at the computer graphics level, the horizontal optimization of the project development timeline is also one of the important factors. Performance optimization cannot be performed after the 3D spatial geometric virtual model modeling and animation effects are completed, because this will cause a large amount of work to be backlogged in the optimization program. It takes too much time to get up. Small optimizations that follow each step of the project, as well as large optimizations that enable final scene synthesis must be proposed.

At present, commonly used 3D space geometry virtual model clipping algorithms include edge shrinkage level-of-detail algorithm, quadratic error measurement algorithm, CPU+GPU cooperative clipping algorithm, etc.

The edge shrinkage level of detail algorithm uses vertex weights to represent the importance of vertices. The vertex weights are sorted according to the degree of influence on the appearance of the model from large to small, and the clipping is controlled within a range with less influence; the weights of vertices are stored in a In the ordinal array, the array order is not only the order of clipping vertices, the advantage is that the algorithm is easy to implement and the execution speed is fast. The limitation of the edge shrinkage level of detail algorithm is that only the vertices are considered, and the whole model is composed of points, lines and surfaces. Only considering the vertices to crop can only better preserve the edge features of the model, which is very important for the overall observability of the model. be greatly affected.

The quadratic error measurement algorithm is based on the improvement of the edge shrinkage level of detail algorithm. The error evaluation is considered in the process of vertex merging. This evaluation is mainly based on the mechanism of boundary constraints and surface normal vectors. The error matrix is used to store the error value. The advantage is that it considers In many aspects of the model attributes, it can achieve better operation results. The limitation of the quadratic error measurement algorithm is that it takes a very long time to calculate the error matrix, and it needs to perform multiple high-dimensional matrix multiplication and matrix inversion operations with high time complexity, which takes a long time for model rendering.

The CPU+GPU cooperative cutting algorithm is completed by the cooperation of the CPU and the GPU. Adjusting the data processing volume of the CPU and the GPU to achieve load balance can maximize the effectiveness of the two. To realize the heterogeneous parallelism of CPU+GPU, it is necessary to coordinate the clock cycle, computing power, storage capacity, thread management, etc. of the two. The advantage is that it has cluster-level parallel support and the unified computing device architecture (CUDA, Compute Unified Device Architecture) provides node-level parallel support. The overall computing performance of the system is greatly improved, and at the same time, it can ensure good running results. The limitation of the CPU+GPU collaborative clipping algorithm is that it needs to be written on the CPU and GPU architecture, and the algorithm logic is very complex and difficult to implement. At the same time, because the algorithm involves underlying hardware calculations, it is often affected by the type of platform hardware and does not have a wide range of applications. supportive.

Contents of the invention

None of the above methods can well coordinate the problems of speed, effect, cross-platform and easy implementation in 3D space model rendering. In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a three-dimensional geometric virtual model level-of-detail clipping method based on points, lines and planes. The transformation, combined with the improved LOD clipping method, was successfully applied to the LOD clipping problem of three-dimensional geometric virtual models.

The level of detail algorithm describes that when the object is far away from the camera, a lower-resolution model can be used, that is, the complexity is lower than that of the prototype, but due to the longer distance, the difference is subtle and invisible. How to reduce the complexity of the 3D model without affecting the visual effect has always been the focus of the level of detail algorithm. Since the model is simplified, the rendering speed of the model will be improved to a certain extent, and the number of vertices and triangles rendered will be reduced.

The present invention is based on the three-dimensional space geometric virtual model level of detail cutting method based on point, line and plane, and the specific method is as follows:

(1) Split grid attributes and create an ordered index list

By separating the original mesh vertex attributes, vertex normal attributes, grid texture attributes, grid color attributes, and triangles, the triangle arrays corresponding to different materials are obtained, and each triangle array is merged into different sub-grid arrays. In order to quickly and efficiently perform the subsequent double-vertex search, an ordered index list needs to be established, and the ordered vertex index list is finally arranged in order of xyz from small to large. The ordered vertex index list is finally arranged with the three-dimensional coordinate values of the vertices, according to the priority order of x, y, and z coordinates, from small to large; for example, a(2,5,7) and b(2,8,4) are The coordinate value of a is less than b, because a.y<b.y.

(2) Find the position sharing attribute vertex and the texture sharing attribute vertex

The main basis for this system to simplify vertices is to remove similar vertices and retain independent vertices or important vertices. If there are common vertices in multiple sub-grids, it means that the vertices are shared by multiple materials and belong to important vertices. To find them, By traversing each vertex of the triangle array, find the coexisting vertices of the sub-grid; by passing the vertex coordinates to be searched into the ordered index list for traversal, find the same vertex index. Here, the sub-grid coexisting vertex and the common index in the ordered list are the position sharing attribute vertex and the texture sharing attribute vertex.

(3) Establish associative triangle array and adjacent triangle array

Each vertex is shared by many triangles. Obtaining these triangles plays a key role in the subsequent algorithm. The triangle array value is the index of the vertex, and the same index can be merged.

Since the three corners of each triangle have many adjacent triangles, the above method only associates each vertex with the subscript of the relevant triangle, but does not extract the specific triangle array according to the vertices. This method is an improvement on the previous method As a supplement, for each vertex, by comparing the x, y, z coordinate values, when the coordinate values of a certain vertex of two triangles are equal, it means that the two are adjacent triangles; so you can get the triangle with all the same values by the vertex Array to get all the adjacent triangles, which will be used later when calculating the vertex angle sum and stretching the texture.

Split the three vertices of the current triangle, get the triangle group associated with the first vertex, add the group to the empty adjacent triangle array, then add the group to the traversed triangle group, and set Unique group number, get the triangle group associated with the second and third vertices, if the triangle array has been traversed, discard the currently obtained triangle, if not, add it to the adjacent triangle array, add this group to the traversed triangle Group, set a unique group number for this group of adjacent triangle groups.

(4) Calculate vertex angles and weights

Each vertex in the mesh is actually shared by many adjacent triangles, and the sum of the angles of these shared vertices determines the unique position of the vertex in the mesh. If the sum is 0 degrees, it belongs to the simplified vertex; if the sum is 180 degrees, the vertex is on the edge of the mesh; if the sum is 360 degrees, the vertex is inside the mesh. Adjacent edges are created using the vector difference of two vertices. Using the previous adjacent triangles, sum all the angles to get the total degree, and the weight can be calculated by the following formula:

Vertex_Weight = Sub_Vertex_Weight + 1

Side_Weight+=Vertex_Weight*Area

Side_Weight+＝Angle*Side_Length

Side_Weight+＝Total_Angle*Area

Side_Weight+＝(New–Old)*Total_Angle*Area

Among them, Vertex_Weight represents the weight of the coordinate value, Sub_Vertex_Weight represents the weight of the sub-vertex, Side_Weight represents the weight of the side, Area represents the area of the triangle corresponding to the side, Angle represents the angle of the vertex on the side, Side_Length represents the length of the side, and Total_Angle represents the angle and sum of the triangle corresponding to the side , New and Old indicate the change of the triangle before and after edge folding (referring to the change of the coordinate values of the three points of the triangle, causing changes in the angle and area of the triangle and other changes such as textures).

(5) Calculate the weight of the triangle center distance

Vertex center distance refers to the distance between the vertex and the center of the grid bounding box. Usually, we use it to determine whether the mesh surface is offset. The triangle center distance is equal to the distance from the three vertices to the center. In order to facilitate comparison before and after edge folding The center distance difference of the vertex will not be empty due to a folded vertex. This system uses the average center distance of the triangles related to the vertex to replace the center distance value of the vertex itself. The weight can be calculated by the following formula :

Weight1=(New–Old)*Normal

Weight2=(New–Old)*Total_Center_Distance

Side_Weight+＝Weight1*Weight2

Among them, Weight1 represents the normal weight, Normal represents the triangle normal value, Weight2 represents the center distance weight, Total_Center_Distance represents the center distance value, and the meanings of other parameters with the same name are the same as those described above.

(6) Calculate the weight based on the texture and area change

The subscript of the texture array split in the grid is the index of the vertex. When we simplify the grid, it will inevitably cause the deformation of the texture, but to minimize the deformation, get the three vertices of the triangle, read Take the UV array to obtain the texture coordinates of the three vertices, find the area of the triangle and the area of the texture, and loop through the detection of the changes in the area of the triangle and the area of the texture when the three vertices are merged in pairs, and record the values of the areas before and after. You can use the following formula to calculate the weights:

Side_Weight+＝Weight+(New–Old)*Area

Side_Weight+＝Weight+(New–Old)*UV_Area

Among them, Weight represents the original weight of the folded edge, UV_Area represents the texture area, and the meanings of other parameters with the same name are the same as those described above.

(7) Clipping importance selection

The first is edge folding processing. Edge folding is to select the least important edge in a triangle for folding, which will result in the merging of two vertices. In order to simplify the calculation, it will eventually be merged into one of the vertices instead of recalculating a new vertex. coordinate of. According to the definition of the three sides of the triangle and the forward and reverse directions, there are a total of six folding methods, that is, ∠1→∠2 (the first corner is folded to the second corner), ∠2→∠1, ∠1→∠3, ∠3→∠1, ∠2→∠3, ∠3→∠2.

After the edge folding is completed, a new grid should be recreated, and all attribute data of the new grid should be created at the same time, a new vertex array and data such as normal, texture, and color in the vertex attributes should be created, and the new vertices should be recorded. If loop traversal Determine whether each vertex is folded, add the folded vertex array to the vertex array of the new grid, add the folded texture coordinates to the new grid texture coordinates, and add the folded vertex color array to The vertex color array of the new mesh, which records the vertices added to the new mesh.

According to the relationship between triangles and vertices in the old mesh, it is corresponding to the new mesh. The triangles of the three-dimensional geometric model mesh carry the connection between vertices. If triangles are not created, elements such as model textures cannot work normally. The addition of vertices will cause grid confusion. Extract each triangle of the old triangle array and change its corresponding sub-grid subscript to determine whether all three vertices have been added to the new grid (edge Fold), if true, add the triangle to the new triangle array, set the new group number and add the group number to the new triangle group number list, fill the last part of the subgrid to form a complete subnetwork grid array.

Remove the folded triangles with an area of 0 to simplify the mesh complexity. At the same time, remove their corresponding grid subscripts, record the removed triangles, and save their corresponding vertices, texture coordinates, and vertex color data. Remove them together and update the vertex index corresponding to the new triangle array.

When clipping a higher level, the camera is very far away from the model itself, and the subtle changes in the mesh cannot be noticed, but the small area in the mesh often occupies a large proportion, removing the effect on the number of rendered triangles will be much lower. Too much removal often affects the visual effect, so it is not merged with the method of removing empty triangles. Before simplifying, the parameter of this value needs to be set separately. According to the incoming value, the high-level weight is calculated, and the new triangle array is traversed. Calculate the area of each triangle taken out, the total area of the triangle group, the number of triangles, determine the maximum area to be removed according to the input value, traverse the new triangle array, remove all triangles smaller than the maximum area, and remove all the triangles The corresponding subgrid index.

Create a new grid: Unify the new data generated above for grid drawing, the new vertex array covers the model vertex array, the new normal array covers the model normal array, the new vertex color array covers the model vertex color array, and the new sub-grid subscript array Override model sub-grid subscript array.

Aiming at the rendering characteristics of the three-dimensional geometric virtual model, the invention solves the rendering problem of the three-dimensional geometric virtual model based on three different levels of point, line and surface. Compared with the traditional geometric model rendering optimization method, the method proposed in this invention achieves the unity of ease of implementation and high efficiency. All calculations are simply calculated on the basic attributes of the distance, area and length of the model itself, and the To achieve a realistic effect, the simplified geometric model cut out is closer to the appearance of the original model. The method of the present invention performs weight calculation based on the most basic point, line, and surface attributes of three-dimensional space geometry. The calculation is simple, easy to implement, and has high execution efficiency. The underlying hardware computing can be used across platforms without modification.

Description of drawings

Fig. 1 is the flow chart of the present invention's level-of-detail clipping method based on point-line-surface three-dimensional geometric virtual model;

Fig. 2 is the three-dimensional space geometry virtual model prototype of the present invention;

Fig. 3 is the three-dimensional space geometry virtual model grid prototype of the present invention;

Fig. 4 is an example of the texture sharing mark of the three-dimensional geometric virtual model of the present invention;

Fig. 5 is an example of the location sharing mark of the three-dimensional geometric virtual model of the present invention;

Fig. 6 is the cutting effect diagram of the first layer of the three-dimensional space geometry virtual model of the present invention;

Fig. 7 is the second layer cutting effect diagram of the three-dimensional space geometry virtual model of the present invention;

Fig. 8 is the cutting effect figure of the third layer of the three-dimensional space geometry virtual model of the present invention;

Fig. 9 is a cutting effect diagram of the fourth layer of the three-dimensional geometric virtual model of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

The present invention is based on the three-dimensional space geometric virtual model level of detail cutting method based on points, lines and planes. The flow chart of the method is shown in Figure 1, and its specific implementation steps are as follows:

Step 1: Separate the original mesh vertex attributes, vertex mid-normal attributes, grid texture attributes, grid color attributes and original triangle sets of the geometric model; create a sorted array for the extracted vertex sets, and create a sequence index list;

The second step: through the triangle set in the first step, find and mark the vertices with texture sharing properties in the original mesh of the model; through the ordered index list in the second step, find the vertices with the position in the original mesh of the model Share attribute vertices and mark them;

Step 3: Through the set of marked triangles in the second step, according to the original vertex coordinates, establish an array of associated triangles of the model mesh; through the previous associated triangle array, establish an array of adjacent triangles of the model mesh according to shared vertices or edges ;

The fourth step: through the adjacent triangle array in the third step, according to the calculation formula in (4), calculate the angle sum of each vertex and calculate the weight;

The fifth step: through the adjacent triangle array in the third step, according to the calculation formula in (5), calculate the center distance of each triangle and calculate the weight;

Step 6: By judging the changes in texture and triangle area before and after folding, calculate the relevant edge weights according to the calculation formula in (6);

Step 7: Add all the above weights in the form of vectors. If the calculation of the entire model is completed, the loop ends, otherwise jump to the fourth step; The area is reserved, and the unimportant or unimportant area is cropped to complete the simplification of the entire complex model.

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

In order to make the effect of the clipping method representative, the number of vertices in the selected three-dimensional space geometric virtual model is more than ten thousand, and it has multiple sub-grids at the same time. The original model is shown in Figure 2.

Step 1: Through the meshing operation of the original model, as shown in Figure 3, the original mesh vertex attributes of the geometric model, the normal line attributes in the vertices, the grid texture attributes, the grid color attributes and the original triangle collection can be extracted and separate out;

The second step: through the triangle set in the first step, find the vertices with texture sharing attributes in the original mesh of the model, as shown in Figure 4, and mark them; through the ordered index list in the second step, find the original model The vertices in the grid with the position sharing attribute, as shown in Figure 5, are marked;

Step 3: Through the set of marked triangles in the second step, according to the original vertex coordinates, establish an array of associated triangles of the model mesh; through the previous associated triangle array, establish an array of adjacent triangles of the model mesh according to shared vertices or edges ;

Step 4: Through the array of adjacent triangles in the third step, calculate the angle sum of each vertex and calculate the weight. Since the model has 24222 vertices, 19712 triangles, and 6 subgrids, Vertex_Weight, Angle and Total_Angle are arrays with a length of 24222; Sub_Vertex_Weight has an array with a length of 6; Side_Weight and Area are the lengths of the matching triangles The sequence of:

Vertex_Weight[24222]=Sub_Vertex_Weight[6]+1

Side_Weight[19712*3]+＝Vertex_Weight[24222]*Area[19712]

Side_Weight[19712*3]+＝Angle[24222]*Side_Length[19712*3]

Side_Weight[19712*3]+＝Total_Angle[24222]*Area[19712]

Side_Weight[19712*3]+＝(New–Old)*Total_Angle[24222]*Area[19712]

Step 5: Through the array of adjacent triangles in the third step, calculate the center distance of each triangle and calculate the weight. Both Normal and Total_Center_Distance are related to the total number of triangles:

Weight1=(New–Old)*Normal[19712]

Weight2=(New–Old)*Total_Center_Distance[19712]

Side_Weight[19712*3]+＝Weight1*Weight2

Step 6: Determine the texture and triangle area changes before and after folding, and calculate the relevant edge weights. UV_Area is also related to the total number of triangles:

Side_Weight[19712*3]+＝Weight+(New–Old)*Area[19712]

Side_Weight[19712*3]+＝Weight+(New–Old)*UV_Area[19712]

Step 7: Add all the above weights in the form of vectors. If the calculation of the entire model is completed, the loop ends, otherwise jump to the fourth step; The area is reserved, and the non-important or unimportant area is cropped.

By observing the distance of the model, the degree of simplification of the model can be divided into 4 levels, that is, there are 4 distances of the observation model. As the distance becomes farther and farther, the complexity of the rendering model is reduced accordingly. Generally speaking, the 4 levels are A more appropriate value, the final effect is shown in Figure 6-9, and the simplified operation of the entire complex model is completed.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (8)

1. A three-dimensional space geometric virtual model detail level cutting method based on a point line surface is characterized by comprising the following steps:

the first step is as follows: separating the original mesh vertex attribute, vertex normal attribute, lattice surface map attribute and lattice surface color attribute of the geometric model from the original triangle set, establishing a sequencing array for the extracted vertex set, and establishing a sequencing index list;

the second step is that: searching the vertex with the texture sharing attribute in the original mesh of the model through the separated triangle set, and marking; searching a vertex with a position sharing attribute in the original mesh of the model through the ordered index list, and marking;

the third step: establishing a model mesh association triangle array according to the original vertex coordinates through the triangle set containing the marks; establishing an adjacent triangle array of the model mesh according to the shared vertex or edge through the associated triangle array;

the fourth step: calculating the angle sum of each vertex and calculating the weight through the adjacent triangle array;

the fifth step: calculating the center distance of each triangle and calculating the weight through the adjacent triangle arrays in the third step;

and a sixth step: calculating the weight of the related side by judging the area changes of the map and the triangle before and after folding;

the seventh step: and adding all the weights in a vector form, comparing the importance of the regions according to the height of the weights, reserving the regions with high importance, and cutting the regions which are not important or unimportant to finish the simplification operation of the whole model.

2. The method for clipping detail levels of a three-dimensional space geometric virtual model based on a point, a line and a surface as claimed in claim 1, wherein the step four includes calculating the sum of angles of each vertex and calculating the weight: using the adjacent triangles, summing all angles to obtain a total number of degrees, and calculating the weight by the following formula:

Vertex_Weight＝Sub_Vertex_Weight+1

Side_Weight+＝Vertex_Weight*Area

Side_Weight+＝Angle*Side_Length

Side_Weight+＝Total_Angle*Area

Side_Weight+＝(New–Old)*Total_Angle*Area

wherein, vertex _ Weight represents the coordinate value Weight, sub _ Vertex _ Weight represents the Sub-Vertex Weight, side _ Weight represents the Side Weight, area represents the Area of the triangle corresponding to the Side, angle represents the Angle of the Vertex on the Side, side _ Length represents the Side Length, total _ Angle represents the Angle sum of the triangle corresponding to the Side, and New and Old represent the triangle change before and after the Side is folded.

3. The method for clipping detail levels of a three-dimensional space geometric virtual model based on a point, a line and a surface as claimed in claim 2, wherein the step five is to calculate the center distance of each triangle and calculate the weight as follows: the average center distance of the triangle related to the vertexes is calculated to replace the center distance value of the vertexes, and the weight is calculated through the following formula:

Weight1＝(New–Old)*Normal

Weight2＝(New–Old)*Total_Center_Distance

Side_Weight+＝Weight1*Weight2

wherein Weight1 represents the Normal Weight, normal represents the triangle Normal value, weight2 represents the Center Distance Weight, and Total _ Center _ Distance represents the Center Distance value.

4. The method for clipping the detail level of the three-dimensional space geometric virtual model based on the point, line and surface as claimed in claim 3, wherein the calculating the relevant edge weight in the sixth step specifically comprises: obtaining three vertexes of a triangle, reading a mapping array to obtain mapping coordinates of the three vertexes, solving the area of the triangle and the area of the mapping, circularly detecting the change of the area of the triangle and the change of the area of the mapping when the three vertexes are combined in pairs, recording the front area value and the rear area value, and calculating the weight through the following formula:

Side_Weight+＝Weight+(New–Old)*Area

Side_Weight+＝Weight+(New–Old)*UV_Area

where Weight denotes the folding edge original Weight and UV _ Area denotes the tile Area.

5. The method for clipping the detail level of the three-dimensional space geometric virtual model based on the point line surface as claimed in claim 1 or 2, wherein the first step is specifically as follows:

the method comprises the steps of obtaining triangular arrays corresponding to different materials by separating vertexes, normals, maps, vertex colors and triangles, combining all the triangular arrays into different sub-grid arrays, and in order to enable double-vertex searching to be conducted quickly and effectively, an ordered index list needs to be established, and the ordered vertex index list is finally arranged from small to large according to the priority sequence of x, y and z coordinates by the three-dimensional coordinate values of the vertexes.

6. The method for clipping the detail level of the three-dimensional space geometric virtual model based on the point line surface as claimed in claim 1 or 2, wherein the second step is specifically as follows:

removing similar vertexes, reserving independent vertexes or important vertexes, if common vertexes in a plurality of sub-grids can exist, indicating that the vertexes have multiple material shares and belong to the important vertexes, finding out the important vertexes, and finding out the vertex where the sub-grids coexist by traversing each vertex of the triangular array; and (3) introducing vertex coordinates to be searched into the ordered index list for traversal, and finding out the same vertex index, wherein common indexes in the coexisting vertex of the sub-mesh and the ordered list are the vertex of the position sharing attribute and the vertex of the texture sharing attribute.

7. The point-line-surface based three-dimensional space geometric virtual model detail level cutting method according to claim 1 or 2, characterized in that the third step is specifically:

splitting three vertexes of a current triangle, obtaining a triangle group associated with a first vertex, adding the group into an empty adjacent triangle array, then adding the group into a traversed triangle group, setting a unique group number for the adjacent triangle group, obtaining triangle groups associated with a second vertex and a third vertex, discarding the currently obtained triangle if the triangle array has been traversed, adding the group into an adjacent triangle array if the triangle array has not been traversed, adding the group into the traversed triangle group, and setting a unique group number for the adjacent triangle group.

8. The point-line-surface based three-dimensional space geometric virtual model level of detail clipping method according to claim 1 or 2, wherein the seventh step of clipping the model specifically comprises:

firstly, edge folding is carried out, wherein edge folding is to select the edge with the lowest importance degree in a triangle for folding, so that two vertexes are merged, and in order to simplify calculation, the edge folding is finally merged to one vertex instead of recalculating the coordinates of a new vertex;

after the edge folding is completed, a new grid is created again, all attribute data of the new grid are created at the same time, a new vertex array and normal line, chartlet and color data in vertex attributes are created, the new vertex is recorded, the loop traversal is used for judging whether each vertex is folded or not, the vertex array after the folding is completed is added to the vertex array of the new grid, the chartlet coordinate after the folding is completed is added to the chartlet coordinate of the new grid, the vertex color array after the folding is completed is added to the vertex color array of the new grid, and the vertex added into the new grid is recorded;

according to the relation between a triangle and a vertex in an old grid, the triangle is corresponding to a new grid, the triangle of a three-dimensional space geometric model grid bears the relation between the vertex and the vertex, each triangle of an old triangle array is extracted, the subscript of a sub-grid corresponding to the triangle is changed, whether the three vertices are added into the new grid or not is judged, if the three vertices are true, the triangle is added into the new triangle array, a new group number is set and added into a new triangle group number list, and the last part of the sub-grid is filled to form a complete sub-grid array;

removing the triangle with the folded area of 0, simplifying the complexity of the grid, simultaneously removing the subscript of the corresponding grid, recording the removed triangle, removing the vertex, the chartlet coordinate and the vertex color data corresponding to the triangle, and updating the vertex index corresponding to the new triangle array;

setting parameters of the values before simplification for small areas in the grids, calculating high-level weights according to the input values, traversing a new triangle array, solving the area, the total area and the number of triangles of each triangle group, determining the removed maximum area according to the input values, traversing the new triangle array, removing all triangles smaller than the maximum area, and removing sub-grid subscripts corresponding to the triangles;

creating a new grid: and uniformly drawing the grids of the new data generated in the previous step, wherein the new vertex array covers the model vertex array, the new normal array covers the model normal array, and the new vertex color array covers the model vertex color array, and the new sub-grid subscript array covers the model sub-grid subscript array.

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