A method for constructing a three-dimensional expression form basic geographic entity considering morphological constraints

Abstract

The application discloses a kind of three-dimensional expression form basic geographic entity construction method considering morphological constraint, it is related to electronic information technical field, including the following steps: the vertex of the ground plot in land class map is based on elevation data acquisition elevation information, and according to the set elevation difference and slope threshold reservation geographic entity two-dimensional graph element within the point that shows topographic feature, the present application fully integrates land class map and elevation data, uses triangulation method to obtain the triangle net information of the basic geographic entity body graph element, is stored in three-dimensional model data format, material library is the rendering material of basic geographic data, more close to actual, realizes the stereoscopic of basic geographic entity, entity and semantic, simultaneously, this method solves the problem that topographic feature is simple to construct multiple types of basic geographic data, saves the tedious artificial modeling procedure, realizes that stock data is quickly converted into three-dimensional expression form basic geographic entity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electronic information technology, and in particular to a method for constructing a three-dimensional expression form basic geographic entity considering morphological constraints. BACKGROUND

[0002] The basic geographic entity is a geographic entity collected and expressed by basic surveying and mapping, including two-dimensional expression form and three-dimensional expression form basic geographic entities, wherein the three-dimensional expression form basic geographic entity is different from the traditional two-dimensional model and has characteristics such as semanticization, structurization, and entity. The three-dimensional expression form basic geographic entity production method can be divided into two types: one is from geographic scene to geographic entity, that is, producing basic geographic entity data based on collected data; the other is from existing basic geographic information data to geographic entity, that is, converting stock data to produce basic geographic entity data. The method from geographic scene to geographic entity includes tilt photography three-dimensional model generation and laser point cloud generation. These two methods are based on high-precision geographic scene data, respectively use deep learning model and point cloud segmentation method, and automatically identify basic geographic entity data based on geographic scene. The method from existing basic geographic data to geographic entity is mainly artificial modeling, which uses traditional three-dimensional modeling software such as 3DSMax and Sketch Up for artificial modeling, and then pastes textures on the three-dimensional model, which has the disadvantages of large workload, time-consuming and laborious, high production cost, and low efficiency.

[0003] In addition, at present, there is a method for constructing a building entity based on building plot and floor information using ArcGIS software. This method is only applicable to buildings in basic geographic entities. The building plot can be used to constrain the coordinate information of the body graph element in the building entity, and the floor information can be used to constrain the elevation information of the body graph element in the building entity. However, this method is not applicable to geographic entities with complex terrain features. Therefore, a method for constructing a three-dimensional expression form basic geographic entity considering morphological constraints is needed to solve the above problems. SUMMARY

[0004] The present application aims to provide a method for constructing a three-dimensional expression form basic geographic entity considering morphological constraints to solve the problems existing in the prior art mentioned in the background.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0006] A method for constructing a three-dimensional expression form basic geographic entity considering morphological constraints, comprising the following steps:

[0007] S1: (1) Obtain the coordinate information of the body graph element boundary in the geographic entity based on the land plot, and obtain the elevation information of the geographic entity based on the elevation data;

[0008] (2) Obtain the serial number and attribute information of the two-dimensional surface graph element of the geographic entity in the land type plot, traverse the serial number of the two-dimensional surface graph element, and obtain the vertex coordinates (x, y, z) and attribute information of the top surface boundary of the volume graph element in combination with the elevation data, which are used to constrain the boundary of the geographic entity;

[0009] (3) Calculate the elevation difference and slope within a single two-dimensional graph element, and filter the elevation feature points within the two-dimensional graph element according to the elevation information threshold m, including the elevation points and the slope points, which are used to constrain the morphological characteristics of the geographic entity;

[0010] (4) Summarize the vertex coordinates of the volume graph element boundary and the elevation feature points to obtain the vertex information of the volume graph element top surface, including the vertex category, the vertex serial number, the vertex coordinates (x, y, z) and the vertex attribute information X;

[0011] (5) If the bottom height of the basic geographic entity volume graph element is h, summarize the vertex information of the volume graph element bottom surface, including the vertex category, the vertex serial number, the vertex coordinate information (x, y, h) and the vertex attribute information X;

[0012] (6) Summarize the top surface vertex and the bottom surface vertex of the volume graph element to form the vertex information of the basic geographic entity volume graph element;

[0013] S2: (1) Based on the coordinate information (x, y, z) of the summarized surface graph element vertex and the elevation feature points in S1, a triangular mesh set A is generated to construct the top surface and the bottom surface of the basic geographic entity volume graph element by a polygon triangulation method;

[0014] (2) Based on the vertex coordinates of the volume graph element top surface boundary and the bottom surface boundary, a triangular mesh set B is generated to construct the side surface of the basic geographic entity volume graph element;

[0015] S3: The basic geographic entity volume graph element includes a top surface, a side surface and a bottom surface. According to the coordinate information (x, y, z) of the geographic entity surface graph element boundary vertex and the elevation feature points, the triangular mesh set and the land type attribute information X, the vertex information, the triangular mesh information, the material type and the texture coordinate information and other information are stored in the OBJ data format to generate a three-dimensional expression form of the basic geographic entity.

[0016] Preferably, the specific steps of S1 are:

[0017] (1) The land type plot includes the space and attribute information of the geographic entity. The serial number and attribute information of the two-dimensional graph element in the land type plot are obtained by using a geographic spatial data processing package. The boundary vertex coordinates and attribute information of the two-dimensional surface graph element of the geographic entity in the basic land type plot are obtained in combination with the elevation data. The recorded information includes the vertex category, the vertex serial number, the vertex coordinates and the vertex attribute information of the two-dimensional surface graph element;

[0018] (2) Obtain all elevation points or digital elevation model data in the two-dimensional graph element of the plot, calculate the maximum elevation difference and slope; if the elevation difference is large or the plot undulation is large, elevation feature points need to be supplemented in the plot to restore the elevation features of the land class, and the class, serial number, vertex coordinate and vertex attribute information of the elevation feature points are recorded; when screening the elevation feature points, set the maximum height difference and slope threshold;

[0019] (3) Collect the top surface vertex information of the volume element, including vertex class, vertex serial number, vertex coordinate information and vertex attribute information, and the vertex coordinate information contains elevation information, to obtain the vertex information set;

[0020] (4) The top surface vertex of the volume element combines with the bottom height of the volume element to obtain the bottom surface vertex information of the volume element, including vertex class, vertex coordinate and vertex attribute, and the vertex serial number is the vertex serial number plus the number of top surface vertices.

[0021] Preferably, the specific steps of S2 are:

[0022] According to the vertex information set collected in step S1, the triangular mesh information required by the volume element is obtained using the triangular subdivision method, and the triangular mesh records the vertex serial number;

[0023] (1) According to the vertex type, the vertices are divided into two groups, q group includes outer ring vertices, inner ring vertices and elevation feature points, and p group includes inner ring vertices;

[0024] (2) If the outer ring and the inner ring of the polygon do not have concave angles, directly proceed to (3), if the outer ring and the inner ring of the polygon have concave angles, from a certain point, the polygon outer ring or inner ring concave angle is supplemented to a convex angle in the clockwise or counterclockwise direction, and the triangular vertex of the concave angle supplement is recorded, the triangular mesh set for supplementing the concave angle of the outer ring polygon is denoted as c, and the triangular mesh set for supplementing the concave angle of the inner ring polygon is denoted as d;

[0025] (3) Triangular subdivision is performed on the q group vertices and the p group vertices using the triangular subdivision method, to obtain triangular mesh set a and triangular mesh set b respectively;

[0026] (4) Finally, the triangular mesh set of the outer ring polygon should be a-c set, and the triangular mesh set of the inner ring polygon should be b-d set, and the triangular mesh set of the top surface and the bottom surface of the volume element is (a-c)-(b-d), that is, (a-c-b+d) set;

[0027] (5) Two vertices of adjacent top surfaces and two vertices of the same position bottom surface form a rectangular side surface, the rectangular side surface is composed of two triangles, one triangle has two top surface vertices and one bottom surface vertex, and the other triangle has two bottom surface vertices and one top surface vertex; the top surface boundary vertices of the geographic entity volume element are traversed to obtain the side surface triangular mesh set of the volume element.

[0028] Preferably, the specific steps of S3 are:

[0029] (1) Group name (g) is used to construct the land class block group, and the land class information is added in the form of "# land class" in front of the group. If there are multiple land blocks of the same type, the mth land class and the nth block can be recorded as "# land class m_n";

[0030] (2) The attribute information of the two-dimensional expression form of the basic geographic entity is stored in the form of "# attribute";

[0031] (3) The top surface, side surface and bottom surface information of the basic geographic entity is stored in turn;

[0032] (4) Top surface: store the top surface vertex coordinate information (x, y, z) of the nth block land class, including the outer ring vertex, the inner ring vertex and the elevation vertex, the vertex storage order refers to the vertex serial number of step S2, the set (a-c-b+d) is a triangular net list set, and the top surface triangular net information is stored in the form of face (Face, f);

[0033] (5) Bottom surface: the elevation of the top surface vertex is changed to the bottom surface elevation z0, the bottom surface vertex coordinate information (x, y, z0) of the nth block land class is stored, the vertex storage order refers to the vertex serial number of step S2, the vertex serial number is "top vertex serial number+vertex number", and the top surface triangular net information is stored in the form of face (Face, f);

[0034] (6) Side surface: the side surface triangular net information obtained in step S2 is stored in the form of face (Face, f);

[0035] (7) The normal vector information, map information and material file of the top surface, bottom surface and side surface are defined;

[0036] (8) The data of the basic geographic entity is stored in the OBJ format, and the data is opened and viewed by using a three-dimensional model software.

[0037] Compared with the prior art, the beneficial effects of the present application are:

[0038] The present application fully integrates land class map patches and elevation data, uses a triangular subdivision method to obtain triangular net information of a basic geographic entity body graph element, stores in a three-dimensional model data format, uses a material library to render materials for basic geographic data, is more in line with reality, realizes stereoscopic, entity and semantic of the basic geographic entity, solves the problems of simple terrain characteristics of multiple types of basic geographic data, saves the complicated manual modeling procedure, and realizes fast conversion of stock data into three-dimensional expression form basic geographic entity. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The total flow chart for constructing the geographic entity of the present application.

[0040] Figure 2 Flow chart for step S1 of the present application.

[0041] Figure 3 Class diagram and elevation data diagram for the present application.

[0042] Figure 4 Basic geographic entity diagram vertex and elevation feature point diagram for the present application.

[0043] Figure 5 Polygon concave corner supplement schematic diagram for the present application.

[0044] Figure 6 Polygon triangulation schematic diagram for the present application.

[0045] Figure 7 Side triangular net schematic diagram for the present application.

[0046] Figure 8 Flow chart for step S3 of the present application.

[0047] Figure 9 OBJ format file screenshot of the three-dimensional expression form of the basic geographic entity of the present application.

[0048] Figure 10 Three-dimensional expression form of the basic geographic entity and detail diagram for the present application. DETAILED DESCRIPTION

[0049] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application will be further described below in conjunction with specific embodiments.

[0050] Please refer to Figures 1-10 The present application provides the following technical solutions:

[0051] A three-dimensional expression form basic geographic entity construction method considering shape constraints, comprising the following steps:

[0052] S1: (1) Based on the land class diagram patch, the coordinate information of the body diagram vertex boundary in the geographic entity is obtained, and the elevation data is used to obtain the elevation information of the geographic entity;

[0053] (2) Obtain the serial number and attribute information of the two-dimensional surface diagram element of the geographic entity in the land class diagram patch, traverse the serial number of the two-dimensional surface diagram element, and combine the elevation data to obtain the vertex coordinates (x, y, z) and attribute information of the top surface boundary of the body diagram element, which is used to constrain the boundary of the geographic entity;

[0054] (3) Calculate the elevation difference and slope within a single two-dimensional element, filter the elevation feature points within the two-dimensional element according to the elevation information threshold m, including the elevation points and the slope points, to constrain the morphological characteristics of the geographic entity; the smaller the elevation information threshold m, the more elevation feature points, and the higher the elevation precision of the basic geographic entity;

[0055] (4) The vertex coordinates and elevation feature points of the body element boundary are summarized to obtain the vertex information of the top surface of the body element, including the vertex category, vertex serial number, vertex coordinates (x, y, z) and vertex attribute information X;

[0056] (5) If the bottom height of the basic geographic entity body element is h, the bottom surface vertex information of the body element is summarized, including the vertex category, vertex serial number, vertex coordinate information (x, y, h) and vertex attribute information X;

[0057] (6) The top surface vertex and the bottom surface vertex of the body element are summarized to form the vertex information of the basic geographic entity body element;

[0058] The specific steps of S1 are:

[0059] (1) The land parcel includes spatial and attribute information of the geographic entity, and the serial number and attribute information of the two-dimensional element in the land parcel are obtained by using a geographic spatial data processing package (such as GeoPandas). The two-dimensional surface element of the basic land parcel is traversed, and the boundary vertex coordinates and attribute information of the two-dimensional surface element are obtained in combination with the elevation data. The recorded information includes the vertex category, vertex serial number, vertex coordinates and vertex attribute information of the two-dimensional surface element;

[0060] (2) Obtain all the elevation points or digital elevation model data in the land parcel two-dimensional element, calculate the maximum elevation difference and slope, and the maximum elevation difference represents the elevation difference of the land parcel, and the slope represents the relief degree of the land parcel; if the elevation difference is large or the land parcel relief degree is large, the elevation feature points need to be supplemented to restore the land class elevation feature, and the category, serial number, vertex coordinates and vertex attribute information of the elevation feature points are recorded; When filtering the elevation feature points, set the maximum elevation difference and slope threshold; the smaller the threshold, the more the supplemented elevation feature points, and the higher the elevation information precision; the larger the threshold, the fewer the supplemented elevation points, and the lower the elevation information precision. The threshold can be set according to the demand;

[0061] (3) Collecting the top surface vertex information of the body graph element, including vertex category, vertex serial number, vertex coordinate information and vertex attribute information, the vertex coordinate information contains elevation information, and obtaining vertex information set; (a) the vertex category includes the outer ring vertex of the two-dimensional surface graph element, the inner ring vertex of the two-dimensional surface graph element and the elevation feature point; (b) the vertex serial number provides important index information for subsequent triangular index, and the recording order is outer ring vertex, inner ring vertex and elevation feature point, and the serial number increases in turn; (c) the vertex coordinate information (containing elevation information) records spatial information, which is an important parameter of geographical entity; (d) the vertex attribute information includes but is not limited to land attribute, and the land attribute is used for material rendering of basic geographical entity and land class grouping;

[0062] (4) The bottom surface vertex information of the body graph element is obtained by combining the top surface vertex of the body graph element with the bottom height of the body graph element, including vertex category, vertex coordinate and vertex attribute, and the vertex serial number is the vertex serial number plus the number of top surface vertices.

[0063] S2: (1) Based on the coordinate information (x, y, z) of the vertex and the elevation feature point of the surface graph element in S1, a triangular mesh set A is generated by a polygon triangulation method to construct the top surface and the bottom surface of the body graph element of the basic geographical entity; the polygon in the surface graph element has three types, including simple convex polygon, simple concave polygon and complex polygon. The simple concave polygon can be directly triangulated; the simple concave polygon is first supplemented with a concave angle, and the triangulation is performed on the convex polygon after the supplement and the triangular index for supplementing the concave angle is removed; the complex polygon first obtains the triangular index of all vertices and the inner ring polygon triangular index, and then removes the inner ring polygon triangular index in the triangular index of all vertices;

[0064] (2) Based on the vertex coordinate of the top surface boundary and the bottom surface boundary of the body graph element, a triangular mesh set B is generated to construct the side surface of the body graph element of the basic geographical entity;

[0065] The specific steps of S2 are as follows:

[0066] According to the vertex information set collected in step S1, the triangular mesh information required by the body graph element is obtained by using the triangulation method, and the triangular mesh records the vertex serial number;

[0067] (1) According to the vertex type, the vertex is divided into two groups, q group includes outer ring vertex, inner ring vertex and elevation feature point, and p group includes inner ring vertex;

[0068] (2) If the polygon outer ring and inner ring do not have concave angle, directly perform (3), if the polygon outer ring and inner ring have concave angle, from a certain point, the polygon outer ring or inner ring concave angle is supplemented to convex angle in clockwise or counterclockwise direction, and the triangular vertex of the concave angle supplement is recorded, the triangular mesh set for supplementing the concave angle of the outer ring polygon is recorded as c, and the triangular mesh set for supplementing the concave angle of the inner ring polygon is recorded as d;

[0069] (3) Using the triangulation method to triangulate q sets of vertices and p sets of vertices, respectively obtaining triangle mesh set a and triangle mesh set b;

[0070] (4) The triangle mesh set of the last outer ring polygon should be a-c set, the triangle mesh set of the inner ring polygon is b-d set, and the triangle mesh set of the top and bottom surfaces of the body graph element is (a-c)-(b-d), that is, (a-c-b+d) set;

[0071] (5) Two vertices of the adjacent top surface and two vertices of the same position bottom surface form a rectangular side surface, the rectangular side surface is composed of two triangles, one triangle has two top surface vertices and one bottom surface vertex, and the other triangle has two bottom surface vertices and one top surface vertex. The top surface boundary vertices of the geographic entity body graph element are traversed to obtain the side surface triangle mesh set of the body graph element.

[0072] S3: The basic geographic entity body graph element includes a top surface, a side surface and a bottom surface. According to the coordinate information (x, y, z) of the geographic entity surface graph element boundary vertex and the elevation feature point, the triangle mesh set and the land class attribute information X, the vertex information, the triangle mesh information, the material type and the texture coordinate information and other information are stored in the OBJ data format to generate a three-dimensional expression form basic geographic entity. The coordinate information (x, y, z) and the triangle mesh set constitute the basic geographic entity body graph element, the land class attribute information X realizes the semantic characteristics of the basic geographic entity, and the material and texture make the basic geographic entity more realistic.

[0073] The specific steps of S3 are:

[0074] The basic geographic entity body graph element includes a top surface, a side surface and a bottom surface. The elevation of the top surface is the real elevation of the geographic entity, and the elevation of the bottom surface can be set according to the demand, but the elevation of the bottom surface should be less than the lowest elevation of the top surface vertex. Assuming that the bottom surface elevation is z0, the land class graph spot vertex information is stored in the OBJ format.

[0075] (1) Use group (Group name, g) to construct a land class block group, and add land class information in the form of “#land class” in front of the group. If there are multiple same land blocks, the mth and nth land classes can be recorded as “#land class m_n”;

[0076] (2) Store the attribute information of the two-dimensional expression form basic geographic entity in the form of “#attribute”;

[0077] (3) Store the top surface, side surface and bottom surface information of the basic geographic entity in turn;

[0078] (4) Top surface: store the top surface vertex coordinate information (x, y, z) of the nth block of land class, including the outer ring vertex, the inner ring vertex and the elevation vertex, the vertex storage order refers to the vertex serial number of step S2, the set (a-c-b+d) is a triangular net list set, and the top surface triangular net information is stored in a face (Face, f) storage mode;

[0079] (5) Bottom surface: change the elevation of the top surface vertex to the bottom surface elevation z0, store the bottom surface vertex coordinate information (x, y, z0) of the nth block of land class, the vertex storage order refers to the vertex serial number of step S2, the vertex serial number is "top vertex serial number + vertex number", and the top surface triangular net information is stored in a face (Face, f) storage mode;

[0080] (6) Side surface: store the side surface triangular net information of the volume element obtained in step S2 in a face (Face, f) storage mode;

[0081] (7) Define the normal vector information, map information and material file of the top surface, the bottom surface and the side surface;

[0082] (8) Store the data of the basic geographic entity in an OBJ format, and open and view the data using a three-dimensional model software.

[0083] Embodiment 1

[0084] S1: (1) Input the land class plot and elevation data, judge the data type, the land class plot is vector data, and the elevation data is raster data, if the original data type does not meet the requirements, adjust the data format, and the input data refers to the attached Figure 3 ;

[0085] (2) Use a geographic spatial data processing tool to obtain the serial number and attribute of the two-dimensional surface element of the land class plot, a single geographic entity corresponds to a two-dimensional surface element, traverse the two-dimensional surface element of the geographic entity in the land class plot, obtain the polygon outer ring, inner ring vertex coordinate information (x, y) and attribute information of the geographic entity surface element, and the surface element vertex coordinate information is used to constrain the boundary of the basic geographic entity volume element;

[0086] (3) Use a geographic spatial data processing tool to obtain the vertex elevation information (z) obtained in S2;

[0087] (4) Calculate the elevation difference and slope in a block of geographic entity, if the elevation difference and slope are less than the set elevation information threshold, no elevation information point is added; if the elevation difference or slope is less than the elevation information threshold, the point with the maximum value and the slope greater than the threshold is recorded as an elevation feature point, and the coordinate and attribute information of the elevation feature point are recorded, the smaller the set elevation information threshold, the higher the terrain fineness of the basic geographic entity, and the elevation feature point is used to constrain the terrain features of the basic geographic entity;

[0088] (5) Collect the spatial information (x, y, z) and attribute information of the top vertices and the elevation feature points of the top surface of the geographic entity, and the attribute information of the elevation feature points is consistent with the attribute information of the vertices, which constitute the vertices of the top surface triangulation network of the basic geographic entity. Refer to the attached Figure 4 .

[0089] S2: (1) Organize the vertex information collected in S1. For example, for a complex polygon, the vertex categories include outer polygon vertices, inner polygon vertices, and elevation feature points. The vertex order starts with a vertex of the polygon, and is sorted in a clockwise (counterclockwise) direction. The set of top surface vertices is P 顶 (a1, a2, ···, a m b1, b2, ···, b n c1, c2, ··· c o ), where a is an outer ring point, m is the number of outer ring points, b is an inner ring point, n is the number of inner ring points, c is an elevation feature point, and o is the number of elevation feature points. The total number of vertices is (m+n+o). If the polygon has multiple inner rings, the vertices are recorded in order of the inner rings.

[0090] (2) The bottom vertices of the basic geographic entity body element inherit all information of the top vertices except the sequence number and elevation. The bottom vertex recording order should be consistent with the top vertex recording order. Assuming that the height of the bottom surface of the basic geographic entity is h (in the display example, the height of the bottom surface is 1m), the set of bottom vertices P 顶 is obtained from the set of top vertices P 底 (a1, a2, ···, a m b1, b2, ···, b n c1, c2, ··· c o ). The spatial information is (x, y, h), and the bottom vertex sequence number is the same as the top vertex sequence number plus the total number of top vertices (m+n+o).

[0091] (3) Supplement the concave angles of the outer and inner polygons, and record the triangle set of the supplemented concave angles. The method for supplementing the concave angles is described in the attached Figure 5 .

[0092] (4) Use the triangulation method to obtain the triangle set of all points (outer ring, inner ring, and elevation feature points), and remove the triangles used to supplement the concave angles of the outer polygon in (3) to obtain the triangle set List_T 外 .

[0093] (5) Use the triangulation method to obtain the triangle set of the inner ring vertices, and remove the triangles used to supplement the concave angles of the inner polygon in (3) to obtain the triangle set List_T 内If a polygon has multiple inner rings, then multiple sets of triangles are generated.

[0094] (6) Remove the triangle collection List_T 外 List_T 内 The set of triangles contained within is used to obtain the set of triangles that constitute the geographic entity surface primitives, and this set is stored as a triangulation list Q. 顶 For a list of top-plane triangulation meshes, please refer to the attached document. Figure 6 ;

[0095] (7) Set Q 顶 Adding the vertex indices of the triangles to the numbers (m+n+o) gives the triangulation list Q. 底 , as a list of base triangular meshes;

[0096] (8) Traverse the triangular network list Q 顶 Elements, with a step size of 2, select two vertices at a time, then select the list Q. 底 Using two vertices of the same geographical location, construct a quadrilateral with the four vertices, resulting in two triangles. (See attached diagram.) Figure 7 ;

[0097] (9) Compile a list of all lateral triangular meshes based on (8) Q 侧 ;

[0098] (10) Calculate the transformation coefficients of the vertex coordinates (x,y,z) and material coordinates (u,v) of the basic geographic entity, and use them as texture coordinate points;

[0099] (11) Calculate the normal vector of the triangulation of the basic geographic entity so that the front of the triangulation of the top surface of the basic geographic entity faces upward, the front of the triangulation of the side surface of the basic geographic entity faces outward, and the front of the triangulation of the bottom surface of the basic geographic entity faces downward.

[0100] S3: (1) Create a text file, store data line by line, and use the "#" character at the beginning of the sentence to comment on the content of the same line, record data attributes, number and other information, and facilitate data management;

[0101] (2) Write the material library storage location "#material library file", the material library file includes terrain texture materials;

[0102] (3) Enter the land category name, for example, "g road_3", which represents the road with the serial number 3;

[0103] (4) Write the vertex coordinate information, for example, "v 1 1 1", which represents the vertex with coordinates (1,1,1). Write each vertex coordinate into the top face vertex coordinate set P one by one. 顶 The order in which elements and vertices are written is referenced to set P. 顶 The order;

[0104] (5) In the same way as (4), write the bottom vertex coordinate set P row by row 底 , the vertex writing order refers to the order of set P 底 ;

[0105] (6) Write the top triangular mesh information, for example, "f 1 2 3", which represents a triangle formed by vertices with serial numbers 1, 2 and 3, write the triangular mesh list row by row as set Q 顶 ;

[0106] (7) In the same way as (6), write the bottom triangular mesh list Q row by row 底 ;

[0107] (8) In the same way as (6), write the side triangular mesh list Q row by row 侧 ;

[0108] (9) Write the normal vector information and the texture coordinate points row by row, S17-S25 refer to the attached Figure 9 ;

[0109] (10) Return to (2) in step S1, until all the basic geographic entities in the geographic patch are traversed;

[0110] (11) Modify the file format suffix to ".obj", store the ".obj" file and the material library file together to obtain the basic geographic entity in the three-dimensional expression form, which can be directly opened and viewed by using the "3D viewer" of the computer, and the basic geographic entity obtained by the method has rich terrain features.

[0111] Although the embodiments of the present application have been shown and described, it can be understood by those of ordinary skill in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for constructing basic geographic entities in a three-dimensional representation that takes into account morphological constraints, characterized in that, Includes the following steps: S1: (1) Obtain coordinate information of volume element boundaries in geographic entities based on land type patches, and obtain elevation information of geographic entities from elevation data; (2) Obtain the sequence number and attribute information of the two-dimensional surface elements of the geographic entities in the land cover, traverse the sequence number of the two-dimensional surface elements, and combine the elevation data to obtain the vertex coordinates of the top boundary of the volume element. x, y, z ) and attribute information, used to constrain the boundaries of geographic entities; (3) Calculate the elevation difference and slope within a single two-dimensional primitive, and filter the elevation feature points within the two-dimensional primitive according to the elevation information threshold m, including elevation points and slope points, to constrain the morphological characteristics of geographic entities; (4) Summarize the vertex coordinates and elevation feature points of the volume primitive boundary to obtain the vertex information of the top surface of the volume primitive, including vertex type, vertex number, vertex coordinates ( x , y , z ) and vertex attribute information X; (5) If the bottom height of the basic geographic entity is h, summarize the bottom vertex information of the entity, including vertex type, vertex number, and vertex coordinate information. x , y , h ) and vertex attribute information X; (6) The top and bottom vertices of the aggregated geometric elements constitute the vertex information of the basic geographic entity geometric elements; S2: (1) Based on the coordinate information of the vertices and elevation feature points of the summary surface primitives in S1 ( x , y , z Using the polygon triangulation method, a set of triangular meshes A is generated to construct the top and bottom surfaces of basic geographic entity primitives; (2) Based on the vertex coordinates of the top and bottom boundaries of the volume primitive, generate a triangular mesh set B that constructs the side of the basic geographic entity volume primitive; S3: Basic geographic entity primitives include top, side, and bottom surfaces, based on the coordinate information of the boundary vertices and elevation feature points of the geographic entity surface primitives ( x , y , z The triangular mesh set and land type attribute information X are stored in OBJ data format, including vertex information, triangular mesh information, material type and texture coordinates, to generate a basic geographic entity in a three-dimensional representation.

2. The method for constructing basic geographic entities in a three-dimensional representation form considering morphological constraints according to claim 1, characterized in that, The specific steps of S1 are as follows: (1) Land cover features include spatial and attribute information of geographic entities. The sequence number and attribute information of two-dimensional elements in land cover features are obtained by using geospatial data processing packages. The two-dimensional surface elements of geographic entities in basic land cover features are traversed. The boundary vertex coordinates and attribute information of two-dimensional surface elements are obtained by combining elevation data. The recorded information includes vertex category, vertex sequence number, vertex coordinates and vertex attribute information of two-dimensional surface elements. (2) Obtain all elevation points or digital elevation model data in the two-dimensional primitives of the plot, and calculate the maximum elevation difference and slope; If there are large elevation differences or large undulations in the land parcel, it is necessary to add elevation feature points within the land parcel to restore the land type elevation characteristics, and record the category, serial number, vertex coordinates and vertex attribute information of the elevation feature points; when filtering elevation feature points, set the maximum elevation difference and slope threshold. (3) Summarize the top vertex information of the body primitive, including vertex category, vertex number, vertex coordinate information and vertex attribute information. The vertex coordinate information includes elevation information, and obtain the vertex information set; (4) The bottom vertex information of the volume primitive is obtained by combining the top vertex of the volume primitive with the bottom height of the volume primitive, including vertex type, vertex coordinates and vertex attributes. The vertex number is the vertex number plus the number of top vertices.

3. The method for constructing basic geographic entities in a three-dimensional representation form considering morphological constraints according to claim 1, characterized in that, The specific steps of S2 are as follows: Based on the vertex information set summarized in step S1, the triangulation method is used to obtain the triangulation information required for the volume primitive. The triangulation records the vertex sequence number. (1) Based on the vertex type, the vertices are divided into two groups: group q includes outer ring vertices, inner ring vertices and elevation feature points, and group p includes inner ring vertices; (2) If there are no concave angles in the outer and inner rings of the polygon, proceed directly to (3). If there are concave angles in the outer and inner rings of the polygon, start from a certain point and proceed clockwise or counterclockwise to supplement the concave angles of the outer or inner rings of the polygon into convex angles, and record the vertices of the triangles supplemented by the concave angles. The set of triangles used by the outer ring polygon to supplement the concave angles is denoted as c, and the set of triangles used by the inner ring polygon to supplement the concave angles is denoted as d. (3) Use the triangulation method to triangulate the vertices of group q and group p to obtain triangulation set a and triangulation set b respectively; (4) Finally, the triangular mesh set of the outer ring polygon should be set ac, the triangular mesh set of the inner ring polygon should be set bd, and the triangular mesh set of the top and bottom surfaces of the representation primitive should be (ac)-(bd), that is, (ac-b+d) set; (5) Two adjacent top vertices and two bottom vertices at the same position form a rectangular side face. The rectangular side face is composed of two triangles. One triangle vertex is two top vertices and one bottom vertices. One triangle vertices are two bottom vertices and one top vertices. Traverse the top boundary vertices of the geographic entity volume primitive to obtain the volume primitive side triangle mesh set.

4. The method for constructing basic geographic entities in a three-dimensional representation considering morphological constraints according to claim 1, characterized in that, The specific steps of S3 are as follows: (1) Use a group (Group name, g) to construct a land type block group, and add land type information before the group in the form of "#land type". If there are multiple land types of the same type, the m-th type and the n-th land type can be recorded as "#land type m_n"; (2) Store the attribute information of basic geographic entities in two-dimensional representation using the format "#attribute"; (3) Store the top, side, and bottom information of the basic geographic entity in sequence; (4) Top surface: Stores the coordinate information of the vertex of the top surface of the nth land parcel. x , y , z The set includes outer ring vertices, inner ring vertices, and elevation vertices. The vertex storage order refers to the vertex sequence number in step S2. The set (ac-b+d) is the triangulation list set, and the top triangulation information is stored in the face (Face, f) storage method. (5) Bottom surface: Replace the elevation of the top vertex with the elevation of the bottom surface. z 0, Stores the coordinates of the vertices of the bottom surface of the nth land parcel ( x , y , z 0), the vertex storage order refers to the vertex number in step S2, the vertex number is "top vertex number + number of vertices", and the top face triangulation information is stored in face (Face, f) storage mode; (6) Side view: Store the side view triangular mesh information of the volume primitive obtained in step S2 in the face (Face, f) storage method; (7) Define the normal vector information, texture information and material files for the top, bottom and side surfaces; (8) Store the data of basic geographic entities in OBJ format and open and view the data using 3D modeling software.

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