CN111899335B - DEM-based image generation method - Google Patents

Abstract

The application relates to an image generation method based on DEM, which comprises the steps of obtaining a target data file; obtaining an elevation data file or an error data file according to the format of the target data file; respectively constructing a regular grid model for displaying the first image and an irregular triangular grid model for displaying the second image according to the elevation data file; the method solves the problem that the traditional manual numerical value input is easy to make mistakes by reading the target data file, improves the working efficiency, and is convenient for a user to select different models to generate images according to the conditions by constructing a plurality of models to generate the image information of the target data file.

Description

Image generation method based on DEM

technical field

The present application relates to the technical field of image processing, specifically a DEM-based image generation method.

Background technique

The digital terrain model (DTM) is a vector sequence of finite items defined on a two-dimensional area, which uses discretely distributed planes to simulate continuously distributed terrain. And DEM, that is, digital elevation model, is a branch of DTM. It is a digital model that digitally simulates the terrain surface through limited known ground elevation data points, that is, it simulates by establishing a continuous function through different scattered data points on the surface. For the surface model, the elevation of any unknown point on the ground can be obtained by using the constructed function, which is essentially interpolation approximation or surface fitting. DEM can describe and simulate surface morphology in digital form, making it an integral part of spatial data infrastructure, modern surveying and mapping engineering production, quality control, accuracy assessment, and analysis applications. Therefore, the research and application of DEM has great significance. Practical significance. The elevation interpolation of DEM is a key step in generating DEM and plays a vital role in the construction and generation of DEM.

If the calculation of the elevation interpolation of the surface area is performed manually, it will be a boring and cumbersome, physical and intellectual labor with an extremely large workload.

Contents of the invention

(1) Solved technical problems

In order to solve the above problems, this application provides an image generation method based on DEM.

(2) Technical solutions

In order to achieve the above object, the present application provides the following technical solutions: a DEM-based image generation method comprising: obtaining a target data file; according to the format of the target data file, judging to obtain an elevation data file or an error data file; When the format of the target data file is judged to be an elevation data file: construct a regular grid model for displaying the first image and an irregular triangular mesh model for displaying the second image respectively according to the elevation data file; store the regular grid network model or irregular triangular network model.

Preferably, when it is judged according to the format of the target data file that it is an error data file, a warning is given.

Preferably, the elevation data file includes a plurality of discrete points, and each discrete point has plane coordinates (X _i , Y _i ) and elevation coordinates (Z _i ).

Preferably, constructing a regular grid model for displaying the first image according to the elevation data file includes: defining grid width and grid spacing according to the imported elevation data file; determining according to the coordinates of a plurality of discrete points and the grid width The grid area of the regular grid model, the grid area includes a plurality of grid points; determine the plane coordinates (X _i , Y _i ); generating the elevation coordinates (Z _i ) of the corresponding grid points according to the plane coordinates (X _i , Y _i ) of each grid point; generating the first image of the elevation data file.

Preferably, compare the plane coordinates (X _i , Y _i ) of multiple discrete points, and obtain the plane coordinates (X _min , Y _min ) of the smallest discrete point and the plane coordinates (X _max , Y _max ) of the largest discrete point; according to the grid The grid spacing, the plane coordinates (X _min , Y _min ) of the minimum discrete point and the plane coordinates (X _max , Y _max ) of the maximum discrete point obtain the number of rows and columns of the grid area; the plane coordinates of the minimum discrete point (X _min , Y _min ) as the base point, increase the number of rows and columns in turn to generate the plane coordinates (X _i , Y _i ) of each grid point.

Preferably, the elevation coordinate (Z _i ) of the discrete point is obtained by interpolation calculation according to the value of the plane coordinate (X _i , Y _i ) of any discrete point; in turn, according to the plane coordinate (X _i , Y The elevation coordinates (Z _i ) of each discrete point are calculated by numerical interpolation of _i ).

Preferably, the steps of constructing an irregular triangulation model for displaying the second image according to the elevation data file are as follows:

T01, construct a polygon covering all discrete points, and divide multiple initial triangles within the polygon;

T02, take a discrete point Q in the polygon;

T03, take an initial triangle from T01;

T04, judging whether the discrete point Q of T02 is within the circumcircle of the initial triangle, if the discrete point Q of T02 is not within the circumcircle of the initial triangle, repeat steps T03-T04;

T05, if the discrete point Q of T02 is within the circumcircle of the initial triangle, add the initial triangle to the queue of triangles to be split;

T06, judging whether the multiple initial triangles in T01 have been calculated, if not, repeat steps T03-T06;

T07, if the calculation is completed, split all triangles to be split into three sides, and remove duplicate sides;

T08, construct the final triangle with the unremoved split edges and the discrete points Q;

T09, judge whether all the discrete points have been calculated, if not, repeat steps T02~T09;

T10. After the calculation is completed, all the final triangles together constitute the second image of the elevation data file.

Preferably, the steps of constructing an irregular triangulation model for displaying the second image according to the elevation data file are as follows:

S01, connect the two discrete points with the smallest distance as the base edge E _i (P ₁ P ₂ );

S02, divide a plurality of discrete points into the left queue L on the left side of the base edge E _i (P ₁ P ₂ ) and the right queue R on the right side of the base edge E _i (P ₁ P ₂ );

S03, judging whether a triangle can be constructed to the left of the base edge E _i (P ₁ P ₂ ), if possible, generate a triangle to the left of the base edge E _i (P ₁ P ₂ );

S04, if the triangle cannot be constructed, then take a discrete point P _n in the left queue L, and calculate the distance sum D between the discrete point P _n and the two ends P ₁ P ₂ of the base edge E _i ;

S05, judging whether the distance sum D is less than the minimum record value, the initial value is infinity, if not less than the minimum record value, then repeat steps S04-S05;

S06, if it is less than the minimum record value, record the discrete point P _n ;

S07, judging whether all the discrete points of the left queue L have been compared, if not, repeat steps S04-S07;

S08, if the comparison is completed, then generate a triangle on the left of the base edge E _i (P ₁ P ₂ );

S09, repeating steps S03-S08 to generate a triangle on the right side of the base edge E _i (P ₁ P ₂ );

S10, the triangle on the left of the base edge E _i (P ₁ P ₂ ) and the triangle on the right of the base edge E _i (P ₁ P ₂ ) together constitute the second image of the elevation data file.

(3) Beneficial effects

Compared with the prior art, the beneficial effects of the present application are: the DEM-based image generation method includes obtaining the target data file; according to the format of the target data file, the elevation data file or the error data file is obtained; according to the elevation data file Constructing a regular grid model for displaying the first image and an irregular triangular network model for displaying the second image respectively; storing the regular grid model or the irregular triangular network model, the method solves the problem by reading the target data file The problem of error-prone traditional manual input values improves work efficiency, and the image information of the target data file is generated by building multiple models, which is convenient for users to choose different models to generate images according to the situation.

Description of drawings

The accompanying drawings are used to provide a further understanding of the application, and constitute a part of the description, and are used to explain the application together with the embodiments of the application, and do not constitute a limitation to the application. In the accompanying drawings:

Fig. 1 shows the flow chart of the image generation method based on DEM of the embodiment of the present application;

Fig. 2 shows the flowchart of forming the grid area according to the embodiment of the present application;

Fig. 3 shows the flowchart of forming grid points according to the embodiment of the present application;

Fig. 4 shows the flow chart that the embodiment of the present application generates grid point elevation value;

Fig. 5 shows the flowchart of generating the second image by the Thiessen polygon method in an embodiment of the present application;

Fig. 6 shows the flow chart of generating the second image by the shortest side length algorithm of the embodiment of the present application;

Fig. 7 shows the computer program of the embodiment of the application to extract the file interface diagram;

FIG. 8 shows an interface diagram of a computer program generating a regular grid according to an embodiment of the present application;

Fig. 9 shows the interface diagram of the TIN generated by the computer program of the embodiment of the present application;

Fig. 10 shows the interface diagram of the computer program preservation file of the embodiment of the present application;

Fig. 11 shows the vector cross product simple figure of the discrete point of the embodiment of the present application;

Fig. 12 shows the numerical arrangement of the elevation data file of the embodiment of the present application.

In the figure: first image 100, second image 200, DEM elevation interpolation interface 10, prompt interface 10a, grid width interface 10b, warning interface 10c, file button 11, open file button 11a, save interpolation file button 11b, Save grid button 11b-1, Save TIN button 11b-2, Generate DEM button 12, Generate Regular Grid button 12a, Generate TIN button 12b, Thiessen polygon method button 12b-1, Shortest distance algorithm button 12b-2, Shortest edge Long Algorithm 12b-3, Zoom In Button 13, Zoom Out Button 14, Display Mode Button 15, Display Shape Button 15a, Display Elevation Display Button 15c, Display Elevation & Shape Button 15b.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of this application.

Referring to accompanying drawing 1-accompanying drawing 12, the embodiment of the present application discloses a kind of image generation method based on DEM, this image generation method based on DEM comprises:

Obtain the target data file; according to the format of the target data file, determine the elevation data file or the wrong data file;

As shown in Figure 12, this method recognizes the internal text of the target data file using a numerical arrangement of N rows and four columns, and the first column is a serial number, and the remaining three columns are data combinations of coordinate values (X, Y, Z). It is judged as an elevation data file, otherwise it is judged as an error data file. When it is judged as an error data file according to the format of the target data file, relevant prompts and warnings can be given to the user so that the user can modify or replace the target data file. It is conducive to the rapid generation of images; among them, the elevation data file is the observation data of real surface points, and the amount of data is relatively large, so that the observation data are all saved in the form of files. This method does not require manual input by the user by reading the file, avoiding A manual input error resulted in the resulting image not being as expected.

When judged to be the elevation data file according to the format of the target data file, a regular grid model for displaying the first image and an irregular triangular network model for displaying the second image are respectively constructed according to the elevation data file;

Specifically, the English abbreviation of the regular grid model is grid, which is a data set of plane coordinates (X, Y) and elevation (Z) of a series of terrain points arranged at equal intervals in the X and Y directions on the Gaussian projection plane . The plane coordinates of any point can be calculated according to the row and column number i, j of the point in the DEM and the basic information stored in the head of the DEM file or the DEM auxiliary file. These basic information should include the coordinates X0, Y0 of the DEM starting point (usually the upper left corner). The interval X0 and Y0 of DEM in the X direction and the Y direction and the number of DEM rows and columns M, N, etc., among which, the X and Y values of the regular grid are realized by a general algorithm, and the elevation value Z is realized by weighted average method, moving surface fitting method, etc. Elevation value interpolation algorithm is realized, the regular grid has the advantages of being easy to use, and can quickly process data through computers, mobile phones and other carriers, and can be widely used in contour calculation, slope aspect calculation, hillside shadow calculation and automatic extraction watershed topography, etc.;

The English abbreviation of the irregular triangular network model is TIN, which is a method to represent the digital elevation model. The algorithm implementation method of the irregular triangular network model can choose the Thiessen polygon algorithm, the shortest side length algorithm, the closest distance algorithm, etc. The difference between the network model and the regular grid model is that the density of sampling points and the location of sampling points are changed according to the complexity of terrain fluctuations, so it can avoid data redundancy when the terrain is flat, and can Such as ridges, valley lines, terrain change lines, etc. represent digital elevation features; users can choose to build regular grid models or irregular triangular mesh models according to their own needs. When the amount of data is small, the user can choose to build a regular grid model; when the data volume of the elevation data file is large and the terrain is more complex, the user can choose to build an irregular triangulation model.

Store regular grid models or irregular triangular mesh models. After the regular grid or irregular triangulation model is constructed and the first image 100 or the second image 200 is displayed, the information of the first image 100 or the second image 200 can be stored in a file format for subsequent viewing and research .

It should also be noted that the first image 100 and the second image 200 are generated from the same elevation data file. Since the first image 100 and the second image 200 are generated in different ways, there are certain differences in structure and details .

Referring to accompanying drawing 7-accompanying drawing 10, in order to carry out above-mentioned method, present embodiment also provides a kind of computer program, this computer program realizes above-mentioned method through programming of computer language and algorithm, so that user can better process elevation data file , and then display the corresponding image information; if the user needs to use the computer program to generate an image, first click the "file" button 11 in the "DEM elevation interpolation" interface 10, and the "DEM elevation interpolation" interface 10 displays " Open File" button 11a and "Save Interpolation File" button 11b, if the user needs to import a new target data file, then click the "Open File" button 10a, and then import the target data file into the program, in the "DEM Height Interpolation" A "prompt" interface 10a will appear in the interface 10, to prompt the file to extract successfully; then click the "generate DEM" button 12 in the "DEM elevation interpolation" interface 10, and then in the "DEM elevation interpolation" interface 10, " Generate Regular Grid" button 12a and "Generate TIN" button 12b;

If the user needs to build a regular grid model to display the first image, he can click the "generate regular grid" button 12a, and if the target data file is a correct elevation data file, a "grid grid" will appear in the "DEM elevation interpolation" interface 10 Grid Width" interface 10b, the user sets the width of the regular grid according to the situation, and then the first image 100 will be displayed in the "DEM Height Interpolation" interface 10, at this time, the "DEM Height Interpolation" interface 10 will display There are "Zoom In" button 13, "Zoom Out" button 14 and "Display Mode" button 15, the user can zoom in on the first image 100 by clicking "Zoom In" button 13 or "Zoom Out" button 14, in addition, click "Display Mode" Button 15 can appear " display shape " button 15a, " display height and shape " button 15b and " display height display " button 15c in " DEM elevation interpolation " interface 10 , if click " display shape " button 15a, in " DEM The shape state of the first image 100 is displayed in the "elevation interpolation" interface 10. If the "display elevation display" button 15c is clicked, the elevation state of the first image 100 will be displayed in the "DEM elevation interpolation" interface 10. Elevation and shape" button 15b will display the elevation and shape state of the first image 100 in the "DEM elevation interpolation" interface 10; if the target data file is an error data file, "DEM elevation interpolation" interface 10 will appear " "Warning" interface 10c to prompt the user to check or replace the target data file.

If the user needs to build an irregular triangulation model to display the second image 200, then click the "generate TIN" button 12b, and then the "Tyson polygon method" button 12b-1, "the closest distance Algorithm" button 12b-2 and "Shortest Side Length Algorithm" button 12b-3, the user can choose to click the corresponding button according to the situation, because the operation mode of the second image 200 generated by this program is the same, only click " Thiessen polygon method "button 12b-1 for illustration, after clicking " Thiessen polygon method " button 12b-1, if the target data file is a correct elevation data file, it will be displayed in the "DEM elevation interpolation" interface 10 The second image 200, at this time, in the "DEM elevation interpolation" interface 10, a "zoom in" button 13, a "zoom out" button 14 and a "display mode" button 15 are displayed, and the user can click on the "zoom in" button 13 or " Zoom out" button 14 zooms the second image 200. In addition, clicking the "display mode" button 15 will appear a "display shape" button 15a, a "display elevation and shape" button 15b and a "DEM elevation interpolation" interface 100. Show elevation display" button 15c, if click " display shape " button 15a, in " DEM elevation interpolation " interface 10, show the shape state of the second image 200, if click " display elevation display " button 15c, will be in " DEM height interpolation " The elevation state of the second image 200 is displayed in the interpolation" interface 10, if the "display elevation and shape" button 15b is clicked, the elevation and shape state of the second image 200 will be displayed in the "DEM elevation interpolation" interface 10; if the The target data file is an error data file, and a "warning" interface 10c appears on the "DEM elevation interpolation" interface 10 to prompt the user to check or replace the target data file.

It should be noted that after the first image 100 or the second image 200 is displayed in the "DEM elevation interpolation" interface 10, the "file" button 11 can be clicked, and then the "save interpolation file" button 11b can be clicked. Click the "Save grid" button 11b-1 or the "Save TIN" button 11b-2 respectively to realize the storage of the first image 100 or the second image 200 of the target data file for subsequent viewing and research.

The elevation data file includes multiple discrete points, each discrete point corresponds to a serial number, and each discrete point has plane coordinates (X _i , Y _i ) and elevation coordinates (Z _i );

Constructing a regular grid model for displaying the first image 100 according to the elevation data file includes:

Define the grid width and grid spacing according to the imported elevation data file, the user can define the grid width by the value of each discrete point in the imported elevation data file, and then determine the grid spacing according to the grid width; according to the value of multiple discrete points Coordinates and grid width determine the grid area of the regular grid model, and the grid area includes multiple grid points;

Specifically, the elevation value of each discrete point is also called the elevation point. By finding the lower left point of all elevation points on a plane position, finding suitable points in turn and connecting them, a polygonal grid including all discrete points is finally generated. grid area, thereby ensuring the correctness of the calculation of the rectangular regular grid when interpolating the elevation value, and at the same time avoiding the calculation at a point far from the elevation point, which will cause the calculation value at this place to deviate too much from the real value, resulting in data distortion. In this embodiment, the generation process of the grid area is shown in Figure 2:

G01, traversing the discrete elevation points, looking for the bottom right corner point of the plane position as the baseline point;

G02, according to the sorting with the baseline point, take the first point and the baseline point and put them into the boundary point sequence;

G03, take out a point from the sequence of sorted discrete points;

G04, judge the positional relationship between this point and the upper two boundary points, and the judgment result is divided into "yes" and "no";

G05, if the judgment result is "Yes", then add this point to the sequence of boundary points;

G06, if the judgment result is "No", delete the previous boundary point from the sequence of boundary points, and repeat steps G04-G06;

Specifically, the positional relationship between this point and the upper two boundary points is judged by means of vector cross product. In this embodiment, the boundary point is based on the vector of the current latest two boundary points (baseline point p and first point a). It is judged by the steering of the line vector between the point b to be determined (the line vector between the baseline point p and the point a), as shown in Figure 11, if the vector pa to the vector pb is a left turn, then the judgment result is "no", and the The previous boundary point (the first point a) is deleted from the boundary point sequence, that is, the vector pa is removed, and the pending point b and the next pending point are judged. If the vector pa to the vector pb' turn right, the judgment result If it is "Yes", the pending point b' is added to the sequence of boundary points.

G07, whether all points are compared, if not, repeat steps G04~G07;

G08, when all points are compared, the sequence of boundary points is output,

G09, the output sequence of boundary points constitutes the grid area of the regular grid model.

After the grid area is determined, the plane coordinates of the grid vertices can be generated according to the plane coordinates of the discrete points and the grid spacing. As shown in Figure 3, each grid point of the grid area is determined according to the coordinates of multiple discrete points and the grid spacing The plane coordinates (X _i , Y _i ); compare the plane coordinates of multiple discrete points, and obtain the plane coordinates (X _min , Y _min ) of the smallest discrete point and the plane coordinates (X _max , Y _max ) of the largest discrete point; according to The grid spacing, the plane coordinates of the minimum discrete point (X _min , Y _min ) and the plane coordinates of the maximum discrete point (X _max , Y _max ) obtain the number of rows and columns of the grid area; the plane coordinates of the minimum discrete point ( X _min , Y _min ) as the base point, increase the number of rows and columns in turn to generate the plane coordinates (X _i , Y _i ) of each grid point.

After the plane coordinates (X _i , Y _i ) of the vertices of the regular grid are generated, the generated vertices can be regarded as unknown points, and the inverse distance weighting method is used to generate the grid vertex elevation (Z _i ) using discrete elevation points; Insert discrete points within a certain range, calculate the product of their weight and elevation, and the sum of all products is the elevation value of the desired point, so that all the points to be inserted in the grid area can be calculated in a loop, as shown in Figure 4 , according to the plane coordinates (X _i , Y _i ) of each grid point, the elevation coordinates (Z _i ) of the corresponding grid points are generated; the first image of the elevation data file is generated, and according to the plane coordinates (X _i , Y _i ) of any discrete point ) values are interpolated to obtain the elevation coordinates (Z _{i )} of the discrete points; in turn _, the elevation coordinates (Z _i ).

It should also be noted that the computer program is mainly programmed in C# language when implementing the regular grid model. Since the generation of the rectangular regular grid and the elevation interpolation are generally constructed at the same time, the same algorithm is also adopted in the programming of this program. At the same time, a rectangular regular grid is constructed and elevation interpolation is performed.

The algorithm runs the main program, method name: Generate

Divide the grid range according to the plane coordinates of the elevation points to generate a boundary polygon. Method name: MakeShell

Divide the plane in the area into grids, and interpolate the elevation value, method name: Divide

In this embodiment, the irregular triangular network model is mainly realized by the Thiessen polygon method, the nearest distance method and the shortest side length method, so that the computer program using this method can combine the efficiency and implementation cost of different algorithms, and then make the computer The program has more contrast and reference value when generating the second image.

Firstly, the Thiessen polygon method will be explained. Using the Thiessen polygon method to build an irregular triangulation model, firstly, according to the plane coordinates of the discrete points, two large triangles containing all discrete points are generated. The large triangle generally does not contain discrete points, and then Select discrete points one by one, and split the large triangle affected by the discrete points into multiple new triangles according to the geometric properties of the Dilony triangle, and so on until all points are calculated. Finally, the triangles irrelevant to the discrete points are eliminated, which is the TIN obtained for survival.

As shown in accompanying drawing 5, the specific construction steps of this irregular triangular network model are as follows:

T01, construct a polygon covering all discrete points, and divide multiple initial triangles within the polygon;

T02, take a discrete point Q in the polygon;

T03, take an initial triangle from T01;

T04, judging whether the discrete point Q of T02 is within the circumcircle of the initial triangle, if the discrete point Q of T02 is not within the circumcircle of the initial triangle, repeat steps T03-T04;

T05, if the discrete point Q of T02 is within the circumcircle of the initial triangle, add the initial triangle to the queue of triangles to be split;

T06, judging whether the multiple initial triangles in T01 have been calculated, if not, repeat steps T03-T06;

T07, if the calculation is completed, split all triangles to be split into three sides, and remove duplicate sides;

T08, construct the final triangle with the unremoved split edges and the discrete points Q;

T09, judge whether all the discrete points have been calculated, if not, repeat steps T02~T09;

T10, after the calculation is completed, all the final triangles together constitute the second image of the elevation data file.

In the computer program of the present embodiment, the programming of using the Thiessen polygon method to construct the irregular triangular network model is as follows:

The algorithm runs the main program, method name: VoronoiTIN

Create TIN according to the geometric properties of Dilony triangle, method name: CreateTriangle

From the triangles that have been generated, find out the unstable triangles affected by the discrete points according to the geometric properties (circumscribed circle) of the Dilony triangle. Method name: ToTmpList

Split and merge the triangles in the unstable triangle queue, and regenerate the triangles with the current affected discrete elevation points, method name: ReBuild

Because the logic of the shortest side length method and the shortest distance method are similar, only the shortest side length method is described in this embodiment, as shown in Figure 6, the steps of using the shortest side length method to construct an irregular triangular network model are as follows:

S01, connect the two discrete points with the smallest distance as the base edge E _i (P ₁ P ₂ );

S02, divide a plurality of discrete points into the left queue L on the left side of the base edge E _i (P ₁ P ₂ ) and the right queue R on the right side of the base edge E _i (P ₁ P ₂ );

S03, judging whether a triangle can be constructed to the left of the base edge E _i (P ₁ P ₂ ), if possible, generate a triangle to the left of the base edge E _i (P ₁ P ₂ );

S04, if the triangle cannot be constructed, then take a discrete point P _n in the left queue L, and calculate the distance sum D between the discrete point P _n and the two ends P ₁ P ₂ of the base edge E _i ;

S05, judging whether the distance sum D is less than the minimum record value, the initial value is infinity, if not less than the minimum record value, then repeat steps S04-S05;

S06, if it is less than the minimum record value, record the discrete point P _n ;

S07, judge whether all the discrete points of the left queue L have been compared, if not, repeat S04-S07;

S08, if the comparison is completed, then generate a triangle on the left of the base edge E _i (P ₁ P ₂ );

S09, repeating steps S03-S08 to generate a triangle on the right side of the base edge E _i (P ₁ P ₂ );

S10, the triangle on the left of the base edge E _i (P ₁ P ₂ ) and the triangle on the right of the base edge E _i (P ₁ P ₂ ) together constitute the second image of the elevation data file.

In the computer program of the present embodiment, the programming of using the shortest side length method to construct the irregular triangular network model is as follows:

The algorithm runs the main program, method name: ShortestDistance

Find the two points with the shortest distance as the growth base edge, method name: FindPrimeEdge

Starting from the initial side, generate a triangle with the remaining elevation points in turn, method name: MakeTriangle

Distinguish whether a point is on the left or right of a line segment, method name: JudgeRorL

The logic of the shortest distance algorithm is roughly the same as that of the shortest side length algorithm. The only condition for judging a point when generating a triangle is that the distance between the point and the straight line is the shortest. Therefore, the implementation code is roughly the same. The different codes can be expressed as:

It should be noted that the terminology used here is only for describing specific implementations, and is not intended to limit the exemplary implementations according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural, and it should also be understood that when the terms "comprising" and/or "comprising" are used in this specification, they mean There are features, steps, operations, means, components and/or combinations thereof.

The relative arrangements of components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present application unless specifically stated otherwise. At the same time, it should be understood that, for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. Techniques, methods and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods and devices should be considered part of the description. In all examples shown and discussed herein, any specific values should be construed as exemplary only, and not as limitations. Therefore, other examples of the exemplary embodiment may have different values. It should be noted that like numerals and letters denote like items in the following figures, therefore, once an item is defined in one figure, it does not require further discussion in subsequent figures.

Although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications and substitutions can be made to these embodiments without departing from the principle and spirit of the present application. and modifications, the scope of the application is defined by the appended claims and their equivalents.

Claims (2)

1. A DEM-based image generation method, characterized in that, comprising: Get the target data file; According to the format of the target data file, it is judged that the elevation data file or the error data file is obtained; the elevation data file includes a plurality of discrete points, and each discrete point has plane coordinates (X _i , Y _i ) and elevation coordinates ( Z _i ); When judging from the format of the target data file that it is an elevation data file: Constructing a regular grid model for displaying the first image and an irregular triangular network model for displaying the second image respectively according to the elevation data file; Determine the plane coordinates (X _i , Y _i ) of each grid point in the grid area according to the coordinates of multiple discrete points and the grid spacing; compare the plane coordinates of multiple discrete points to obtain the plane coordinates of the smallest discrete point (X _min , Y _min ) and the plane coordinates of the largest discrete point (X _max , Y _max ); according to the grid spacing, the plane coordinates of the smallest discrete point (X _min , Y _min ) and the plane coordinates of the largest discrete point (X _max , Y _max ) The number of rows and columns of the grid area; take the plane coordinates (X _min , Y _min ) of the smallest discrete point as the base point, increase the number of rows and columns in turn, and generate the plane coordinates (X _i , Y _i ) of each grid point, According to the value of the plane coordinates (X _i , Y _{i )} of any discrete point, the elevation coordinate (Z _{i )} of the discrete point is calculated by interpolation; Numerical interpolation calculates the elevation coordinates (Z _i ) of each discrete point, and generates the first image of the elevation data file; The irregular triangular network model is mainly realized by the Thiessen polygon method, the nearest distance method and the shortest side length method; Using the Thiessen polygon method to construct an irregular triangular network model, the steps of constructing an irregular triangular network model for displaying the second image according to the elevation data file are as follows: T01, construct a polygon covering all discrete points, and divide multiple initial triangles within the polygon; T02, take a discrete point Q in the polygon; T03, take an initial triangle from T01; T04, judging whether the discrete point Q of T02 is within the circumcircle of the initial triangle, if the discrete point Q of T02 is not within the circumcircle of the initial triangle, repeat steps T03-T04; T05, if the discrete point Q of T02 is within the circumcircle of the initial triangle, add the initial triangle to the queue of triangles to be split; T06, judging whether the multiple initial triangles in T01 have been calculated, if not, repeat steps T03-T06; T07, if the calculation is completed, split all triangles to be split into three sides, and remove duplicate sides; T08, construct the final triangle with the unremoved split edges and the discrete points Q; T09, judge whether all the discrete points have been calculated, if not, repeat steps T02~T09; T10, after the calculation is completed, all the final triangles together constitute the second image of the elevation data file; Using the shortest side length method to build an irregular triangular network model, the steps of constructing an irregular triangular network model for displaying the second image according to the elevation data file are as follows: S01, connect the two discrete points with the smallest distance as the base edge E _i (P ₁ P ₂ ); S02, divide a plurality of discrete points into the left queue L on the left side of the base edge E _i (P ₁ P ₂ ) and the right queue R on the right side of the base edge E _i (P ₁ P ₂ ); S03, judging whether a triangle can be constructed to the left of the base edge E _i (P ₁ P ₂ ), if possible, generate a triangle to the left of the base edge E _i (P ₁ P ₂ ); S04, if the triangle cannot be constructed, then take a discrete point P _n in the left queue L, and calculate the distance sum D between the discrete point P _n and the two ends P ₁ P ₂ of the base edge E _i ; S05, judging whether the distance sum D is less than the minimum record value, the initial value is infinity, if not less than the minimum record value, then repeat steps S04-S05; S06, if it is less than the minimum record value, record the discrete point P _n ; S07, judging whether all the discrete points of the left queue L have been compared, if not, repeat steps S04-S07; S08, if the comparison is completed, then generate a triangle on the left of the base edge E _i (P ₁ P ₂ ); S09, repeating steps S03-S08 to generate a triangle on the right side of the base edge E _i (P ₁ P ₂ ); S10, the triangle on the left of the base edge E _i (P ₁ P ₂ ) and the triangle on the right of the base edge E _i (P ₁ P ₂ ) together constitute the second image of the elevation data file; Store regular grid models or irregular triangular mesh models. 2. A method for generating an image based on DEM according to claim 1, characterized in that, when the format of the target data file is judged to be an error data file, a warning is given.

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