CN108830929A - Multi-resolution Terrain pyramid model generation method and system based on database - Google Patents

Abstract

The invention discloses a method and system for generating a multi-resolution terrain pyramid model based on a database. Through the three steps of data acquisition-model generation-data storage, the existing pyramid model method is greatly improved, greatly reducing The time of data search and positioning and the number of I/O times make the data shareable and improve the rendering speed; at the same time, the model data is stored in the database according to the preset rules, which can reduce data redundancy and reduce data preprocessing and storage time , to improve roaming response speed.

Description

Method and system for generating multi-resolution terrain pyramid model based on database

technical field

The invention relates to the field of three-dimensional GIS, in particular to a method and system for generating a multi-resolution terrain pyramid model based on a database.

Background technique

3D terrain visualization is an application technology involving computer graphics, multimedia and geographic information science. It is a process of multi-resolution organization, modeling and rendering of terrain data within a certain area. At present, large-scale 3D terrain visualization technology is widely used in various fields. For example, military simulated combat systems, 3D games, street view navigation, urban planning, etc.

With the continuous development of computer graphics, computer graphics hardware technology and computer storage hardware level, computer simulation and visualization technology is becoming more and more mature, which also gives new impetus to the in-depth development of 3D terrain visualization technology. But even so, for large-scale terrain data of the order of GB or even TB, it will bring great challenges to the real-time rendering of 3D terrain, whether it is in the organization and storage of data or in the calculation and scheduling of data.

In the prior art, the method of constructing a multi-resolution terrain pyramid model is based on DEM (Digital Elevation Model, digital elevation model) data, but it does not consider the ability of computer rendering equipment, and it has rigidity for the width and height of the original data Requirements, that is, the width and height dimensions must be 2 ^N × 2 ^N , but the width and height dimensions of the original data in a certain region cannot just meet the requirements. At the same time, the storage method of terrain data is mainly based on files or folders. This method needs to create a lot of files or folders, and its data organization structure is not compact, the index number is complicated, the data update is slow, and it does not support multi-users in the network environment. operate.

Therefore, in combination with the rapid development of 3D terrain visualization and based on the current situation of our country, designing an operable and cost-effective method is of great significance to the development of 3D GIS field.

Contents of the invention

The present invention is aimed at the challenges brought by the high storage of big data to the real-time rendering of the current 3D terrain in the prior art, and provides a method and system for generating a multi-resolution terrain pyramid model based on a database. Through data acquisition-model generation- The three steps of data warehousing have greatly improved the existing pyramid model method, greatly reducing the time of data search and positioning and the number of I/O times, making the data shareable and improving the rendering speed; at the same time, the model data is Preset rules are stored in the database, which can reduce data redundancy, reduce data preprocessing and storage time, and improve roaming response speed.

In order to achieve the above object, the technical solution adopted in the present invention is: a method for generating a multi-resolution terrain pyramid model based on a database, comprising the steps of:

S1, obtain the original terrain data and perform format conversion to obtain DEM data and DOM data;

S2, using the DEM data and DOM data obtained in S1 to generate a multi-resolution DEM pyramid model and a multi-resolution DOM pyramid model respectively according to the video memory limitation;

S3, storing the data of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model into the database according to preset rules.

As an improvement of the present invention, the step S2 includes:

S21, reading DEM data and DOM data;

S22, determining the number of model layers of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model according to the DEM data and DOM data obtained in S21;

S23. Determine the terrain block size of the DEM data and the DOM data respectively according to the number of model layers and the video memory limit;

S24, performing invalid data filling processing on the DEM data and DOM data;

S25, the DEM data and the DOM data after S24 invalid data filling processing are respectively divided into blocks according to the terrain block size in S23;

S26, calculating the roughness value of each DEM block;

S27, resampling the DEM data and DOM data after block by bilinear interpolation method to generate upper layer data;

S28, repeat steps S25 to S27, until the number of model layers of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model in S22 is reached.

As an improvement of the present invention, in the step S22, the number k of DEM blocks contained in the DOM data is calculated according to the following formula:

k=max(RasterXSize, RasterYSize)/(max(col, row)-1);

Among them, max(RasterXSize, RasterYSize) is the larger value of DOM data width and height, and max(col, row) is the larger value of row and column in DEM data;

The number of model layers n of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model is calculated according to the following formula:

k×2 ⁿ ∈ [512, 1024], calculate the smallest positive integer n.

As another improvement of the present invention, in the step S23, the DEM block size is calculated according to the following formula:

( ²ⁿ +1)×( ²ⁿ +1);

According to the optimal single image size supported by video memory, use the following formula to calculate the DOM block size:

max(RasterXSize, RasterYSize)/(max(col, row)-1)×2 ⁿ

Among them, max(RasterXSize, RasterYSize) is the larger value of DOM data width and height, max(col, row) is the larger value of row and column in DEM data, and n is the multi-resolution DEM pyramid model and the number of model layers for the multi-resolution DOM pyramid model.

As another improvement of the present invention, the step S24 includes: taking the upper left corner of the original terrain data as the origin, performing invalid data filling processing on the original terrain data, so that the rows and columns of the DEM data are both 2 ^N + 1, The width and height of the DOM data are both 2 ^N , where N is the smallest positive integer that enables the filled data to just surround the original terrain data.

As another improvement of the present invention, in the step S26, the terrain roughness value is calculated in advance and stored in the database, and the roughness value of each DEM block is calculated according to the following formula:

Among them, d is the side length of the DEM block, e ₁ ~ e ₆ are the error values of the 6 vertices of the terrain block node, and e ₇ ~ e ₁₀ are the error values of the 4 child nodes of the terrain block node.

As another improvement of the present invention, in the step S27, resampling of every 2×2 data blocks is performed on the original terrain data after the invalid data filling process and block, if every 2×2 data blocks If both original terrain data and invalid filling data are included, the invalid filling data is changed to a value of 0, and then resampling calculation is performed; if only invalid filling data is included in each 2×2 data block, resampling is not performed calculate.

As a further improvement of the present invention, the step S3 includes:

S31, calculate the index number of each DEM block in the multi-resolution DEM pyramid model and the index number of each DOM block in the multi-resolution DOM pyramid model according to the coordinates of the terrain block and the number of layers in the pyramid model number, using the index number as the primary key index;

S32, creating a project in the database, and establishing a multi-resolution DEM pyramid model data table and a multi-resolution DOM pyramid model data table in the project;

S33. Store the data of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model in the form of binary BLOB into the multi-resolution DEM pyramid model data table and the multi-resolution DOM pyramid model data table respectively.

As a further improvement of the present invention, in the step S33, the boundary data of each DEM block is repeatedly stored in the multi-resolution DEM pyramid model data table, and one row is added in the multi-resolution DOM pyramid model data table Record, used to store the original size information and block size information of DOM data.

In order to achieve the above object, the present invention also adopts a kind of technical scheme is: the multi-resolution terrain pyramid model generation system based on database, comprising:

Data acquisition module: acquire the original terrain data and perform format conversion to obtain DEM data and DOM data;

Model generation module: according to the memory limit, use the DEM data and DOM data obtained in the data acquisition module to generate a multi-resolution DEM pyramid model and a multi-resolution DOM pyramid model respectively;

Data storage module: store the data of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model into the database according to preset rules.

Compared with the prior art, the beneficial effect of the present invention is that the present invention abandons the traditional file storage method and adopts the database storage method, which can greatly reduce the time of data search and location and the number of I/O times, and make the data shareable ;The establishment of the model considers the display performance of the video memory, which can make full use of the performance of the computer hardware and improve the rendering speed; store the model data in the database according to the preset rules, which can reduce the redundancy of data, reduce the time of data preprocessing and storage , to improve roaming response speed.

Description of drawings

Fig. 1 is the database-based multi-resolution terrain pyramid model generation method flowchart that the embodiment of the present invention provides;

Fig. 2 is the determination schematic diagram of terrain roughness in the embodiment of the present invention;

Fig. 3 is the schematic diagram of DEM border data storage principle in the embodiment of the present invention;

FIG. 4 is a block diagram of a database-based multi-resolution terrain pyramid model generation system provided by an embodiment of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

Example 1

A database-based multi-resolution terrain pyramid model generation method, as shown in Figure 1, comprises the following steps:

S1. Obtain the original terrain data and perform format conversion to obtain DEM data and DOM data; you can download the original terrain data that needs to be visualized in 3D from LocalSpaceViewer, and use the [Raster to ASCII] function of the ArcToolbox conversion tool in the ArcMap software to convert The downloaded topographic elevation data file in TIFF (Tag Image File Format, tag image file format) format is converted into regular grid DEM data; DOM (Digital Orthophoto Map, digital orthophoto) data remains in the same TIFF format when downloaded.

It should be noted that the regular grid DEM data is generally a text file with the suffix .asc, which contains 6 lines of header information and several lines of elevation data values. In the header information, ncols and nrows represent the number of columns and rows of regular grid terrain data respectively, xllcorner and yllcorner represent the coordinates of the lower left corner of the grid, and cellsize refers to the size of the cell, that is, each grid The size of the unit, NODATA_value means invalid data, and the rest is the elevation data of the corresponding coordinates.

S2, using the DEM data and DOM data obtained in S1 to generate a multi-resolution DEM pyramid model and a multi-resolution DOM pyramid model respectively according to the video memory limitation;

S3, storing the data of the multi-resolution DEM pyramid model and the data of the multi-resolution DOM pyramid model in the database according to the preset rules, the Oracle database can be selected, and the data of the multi-resolution DEM pyramid model and the multi-resolution DOM The data of the pyramid model is stored in the Oracle database according to the preset rules, which is convenient and quick.

Example 2

The difference between this embodiment and Embodiment 1 is that step S2 includes:

S21, reading DEM data and DOM data, such as the number of rows and columns of DEM data, DOM image size, etc. For regular grid DEM data, obtain the larger value max(col, row) of both rows and columns in the DEM data. For DOM data, use the GDAL (Geospatial Data Abstraction Library, spatial data conversion library) function to obtain the larger value max(RasterXSize, RasterYSize) of the width and height of the DOM data.

S22, determine the number of model layers of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model according to the DEM data and DOM data obtained in S21; by formula k = max(RasterXSize, RasterYSize) / (max(col, row)- 1 ) Calculate the number of DEM blocks that can be included in the DOM data. On the premise of the best single image size supported by video memory, that is, the condition k× 2 ⁿ ∈ [512, 1024], the minimum positive integer n is calculated to obtain the number of multi-resolution pyramid layers n .

S23. Determine the terrain block size of the DEM data and the DOM data respectively according to the number of model layers and the video memory limit, and calculate the DEM block size according to the following formula;

( ²ⁿ +1)×( ²ⁿ +1);

According to the optimal single image size supported by video memory, use the following formula to calculate the DOM block size;

max(RasterXSize, RasterYSize)/(max(col, row)-1)×2 ⁿ .

Since the size of the DEM block and DOM block is calculated based on the optimal single image size supported by the video memory and the corresponding relationship between the DEM and DOM data ranges, it can ensure that the computer hardware is fully considered for the original terrain data of any size. It can give full play to the rendering and drawing performance of the video memory, and the rendering and drawing are very smooth. If the optimal single image range supported by the video memory changes, it is only necessary to modify the defined constant value in the program. At the same time, the number of layers of the pyramid model does not need to be set in advance in the program, nor does it need to limit the size of the topmost data in the golden model data. This calculation method can freely control the number of hierarchical layers of the pyramid and the size of the top pyramid model data (not necessarily 2 ⁿ × 2 ⁿ ).

S24, perform invalid data filling processing on the DEM data and DOM data, if the invalid data filling processing is not performed, for the boundary data, if the size does not meet the size requirements of each block when performing the block operation, then For terrain blocks that meet the requirements, it is necessary to calculate how many rows and columns of data should be added and the location of these data, which is not conducive to the terrain block. In this embodiment, padding the original data with invalid data can speed up the terrain block process and avoid repeated calculations at boundaries.

Taking the upper left corner of the original terrain data as the origin, the original terrain data is filled with invalid data, so that the rows and columns of the DEM data are both 2 ^N + 1, and the width and height of the DOM data are both 2 ^N , where N is The smallest positive integer that can make the filled data just surround the original terrain data.

In this way, the invalid data-9999 can be defined to fill the original terrain data with invalid data so that its size meets the requirement.

S25, the DEM data and the DOM data after S24 invalid data filling processing are respectively divided into blocks according to the terrain block size in S23;

S26, calculate the roughness value of each DEM block; calculate the roughness data of the terrain data in advance, which can reduce the time-consuming determination of the required terrain data level in the data scheduling process and calculate the terrain subdivision in the terrain triangulation drawing degree of time-consuming.

As shown in Figure 2, the roughness value of each DEM block can be calculated according to the following formula;

Among them, d is the side length of the DEM block, e ₁ ~ e ₆ are the error values of the 6 vertices of the terrain block node, and e ₇ ~ e ₁₀ are the error values of the 4 child nodes of the terrain block node.

S27, resampling the DEM data and DOM data after block by bilinear interpolation method to generate upper layer data;

The conventional terrain pyramid generation method is: DEM data is sampled every other row and column, and DOM data is sampled by three times convolution method. Due to the different sampling methods of DEM data and DOM data in this method, the image texture (DOM) will be stretched when the texture mapping operation is performed during the terrain visualization process, the quality of the terrain visualization effect is low, and the simulation effect is unreal. At the same time, although the cubic convolution method has high precision and has the function of enhancing the edge, its disadvantages are that the calculation amount is large and the speed is slow, and it takes too much time to use this method to sample large-scale terrain data. In this embodiment, the bilinear interpolation method is used for resampling, which has moderate accuracy and calculation amount, and has its own low-pass filtering function. The edge of the resampled image is relatively smooth and has an average filtering effect. Both DEM data and DOM data use bilinear interpolation, so that they are consistent in the law of data change, and texture stretching will not occur during texture mapping operations.

The resampling process in this step also involves the redefinition of invalid data at the edge of the original terrain data: the original terrain data that has been filled with invalid data and divided into blocks is resampled every 2×2 data blocks, if Each 2×2 data block includes both original terrain data and invalid filling data, then change the invalid filling data to a value of 0, and then perform resampling calculation; if each 2×2 data block only includes invalid If the data is filled, no resampling calculation is performed.

In this way, the invalid data value is not directly defined as 0, but the invalid data value is firstly defined as -9999, and then changed to 0, in order to avoid the inability to accurately determine the original terrain when there are a large number of 0 values in the terrain edge data range, while adding too much redundant data.

S28, repeat steps S25 to S27, until the number of model layers of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model in S22 is reached.

Example 3

The difference between this embodiment and Embodiment 1 is that step S3 further includes:

S31, according to the coordinates of the terrain block and the number of layers in the pyramid model, calculate the index number of each DEM block in the multi-resolution DEM pyramid model and the data of each DOM block in the multi-resolution DOM pyramid model An index number, using the index number as a primary key index;

Calculate the index number of each DEM block data and DOM block data in the multi-resolution pyramid model according to the formula ID =ix*total_row+iy*total*col+lev ; among them, ix and iy are the horizontal and vertical of the current terrain block Coordinates, total_row and total_col are the number of rows and columns of the entire original data, and lev is the resolution level of the current terrain block.

In this embodiment, all the information of the data is fully used in obtaining the serial number. This makes it possible to calculate the layer number of the terrain block in the pyramid model when the number and row number of the terrain block are known. For example, for different layers of data with the same row and column position, the layer number can be known according to the number value.

S32, creating a project in the database, and establishing a multi-resolution DEM pyramid model data table and a multi-resolution DOM pyramid model data table in the project;

In this embodiment, an Oracle database is used to create a project in the database, and a multi-resolution DEM pyramid model data table and a multi-resolution DOM pyramid model data table are established in the project. Store the obtained multi-resolution DEM pyramid model data and multi-resolution DOM pyramid model data in the Oarcle database according to certain rules, and set the terrain block number as the primary key index at the same time, which can reduce data redundancy and data preprocessing and storage time, improving the response speed when roaming the scene.

S33. Store the data of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model in the form of binary BLOB into the multi-resolution DEM pyramid model data table and the multi-resolution DOM pyramid model data table respectively.

In this embodiment, the table named GEO_DATA (that is, the multi-resolution DEM pyramid model data table) is used to store multi-resolution DEM pyramid model data, and the column names are GEO_ID, LEV, GEO, and NORMAL, which are used to store DEM respectively Pyramid model data index ID, hierarchical level lev , elevation value and terrain roughness value; at the same time, for DEM data, because its data volume is much smaller than DOM data volume, so, for the boundary data of each DEM block, in the database In repeated storage, as shown in Figure 3.

The table named TIFF_DATA (that is, the multi-resolution DOM pyramid model data table) is used to store the multi-resolution DOM pyramid model data, and the column names are TIFF_ID, LEV, TIFF, which are used to store the index ID and level of the DOM pyramid model data respectively Level lev , the RGB value of the image; at the same time, add a row to this table to store the original size information and block size information of the DOM data.

Use the OCI (Oracle Call Interface) of the Oracle database to store the model data in the form of binary BLOB into the multi-resolution DEM pyramid model data table and the multi-resolution DOM pyramid model data table respectively, which can speed up the data access process .

In the process of data storage, for DEM data, since its data volume is much smaller than that of DOM data, the boundary data of each DEM block is repeatedly stored in the database. As for DOM data, its data format is TIFF. Although the file quality of this format is high, its compression rate is low and it takes up a lot of memory. In order to avoid storing a large amount of invalid data, the present invention adds a row of records in the table for storing multi-resolution DOM pyramid model data, which is used to store the original size information and block size information of DOM data, so that when scheduling DOM boundary data in the future , the program can calculate the contour information of the boundary data according to the information of the previous column or row.

Example 4

A multi-resolution terrain pyramid model generation system based on a database, including a data acquisition module, a model generation module and a data storage module.

The data acquisition module is used to obtain the original terrain data and perform format conversion to obtain DEM data and DOM data; the model generation module is used to generate a multi-resolution DEM pyramid model and a multi-resolution DOM by using the DEM data and DOM data according to the memory limit Pyramid model; the data storage module stores the data of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model into the database according to preset rules.

In the foregoing embodiments, the technical problems of narrow applicability, large data redundancy, and long time for data search and location are solved in the existing methods. The storage method of the database is used, which can greatly reduce the time of data search and positioning and the number of I/O, and make the data shareable; the establishment of the model considers the display performance of the video memory, and can be applied to terrain data of any size range, making full use of computer hardware The performance of the model improves the rendering and drawing speed; the model data is stored in the database according to the preset rules, which can reduce data redundancy, reduce data preprocessing and storage time, and improve roaming response speed.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned examples. What are described in the above-mentioned examples and descriptions are only to illustrate the principles of the present invention. The present invention also has various changes without departing from the spirit and scope of the present invention. These changes and improvements all fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. The multi-resolution terrain pyramid model generation method based on the database is characterized by comprising the following steps of:

s1, acquiring original terrain data and performing format conversion to acquire DEM data and DOM data;

s2, respectively generating a multi-resolution DEM pyramid model and a multi-resolution DOM pyramid model by utilizing the DEM data and the DOM data acquired in the S1 according to the video memory limitation;

and S3, storing the data of the multi-resolution DEM pyramid model and the data of the multi-resolution DOM pyramid model into a database according to a preset rule.

2. The database-based multi-resolution terrain pyramid model generation method of claim 1, wherein the step S2 includes:

s21, reading DEM data and DOM data;

s22, determining the model layer number of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model according to the DEM data and the DOM data acquired in the S21;

s23, respectively determining the terrain block size of the DEM data and the DOM data according to the model layer number and the video memory limit;

s24, invalid data filling processing is carried out on the DEM data and the DOM data;

s25, partitioning the DEM data and the DOM data subjected to the filling processing of the invalid data S24 according to the size of the terrain partition in the S23;

s26, calculating the roughness value of each DEM block;

s27, resampling the partitioned DEM data and DOM data by a bilinear interpolation method to generate previous-layer data;

s28, repeating steps S25 to S27 until reaching the model level of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model in S22.

3. The database-based multi-resolution terrain pyramid model generation method according to claim 2, wherein in step S22, the number k of DEM blocks included in DOM data is calculated according to the following formula:

k=max(RasterXSize，RasterYSize)/(max(col，row)-1);

wherein max (RasterXSize, RasterYSize) is the larger of both the DOM data width and height, and max (col, row) is the larger of both the rows and columns in DEM data;

calculating the model layer number n of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model according to the following formula:

k×2ⁿ∈[512，1024]meter for measuringThe smallest positive integer n is calculated.

4. The database-based multi-resolution terrain pyramid model generation method of claim 2, wherein in step S23, the DEM partition size is calculated according to the following formula:

(2ⁿ+1)×(2ⁿ+1)；

according to the optimal size of a single image supported by video memory, calculating the DOM block size by using the following formula:

max(RasterXSize，RasterYSize)/(max(col，row)-1)×2ⁿ

wherein max (RasterXSize, RasterYSize) is the larger value of the width and height of the DOM data, max (col, row) is the larger value of the rows and columns in the DEM data, and n is the number of model layers of the multi-resolution DEM pyramid model and the multi-resolution DOM pyramid model.

5. The database-based multi-resolution terrain pyramid model generation method of claim 2, wherein the step S24 includes: and taking the upper left corner of the original topographic data as an origin, and performing invalid data filling processing on the original topographic data to ensure that the rows and columns of the DEM data are both 2^N+1, the width and height of the DOM data are 2^NAnd N is the minimum positive integer which can enable the filled data to just surround the original terrain data.

6. The database-based multi-resolution terrain pyramid model generation method of claim 2, wherein in step S26, terrain roughness values are calculated in advance and stored in the database, and the roughness value of each DEM partition is calculated according to the following formula;

wherein d is the side length of the DEM block,e ₁~e ₆is the topographyThe 6 vertex error values for the block nodes,e ₇~e ₁₀is the 4 child node error values for the terrain block node.

7. The database-based multi-resolution terrain pyramid model generation method according to claim 2, wherein in step S27, original terrain data subjected to invalid data padding processing and blocking is re-sampled every 2 × 2 data blocks, and if every 2 × 2 data blocks include both original terrain data and invalid padding data, the invalid padding data is changed to 0, and then re-sampling calculation is performed; if only invalid padding data is included in every 2 x 2 data blocks, no resampling calculation is performed.

8. The database-based multi-resolution terrain pyramid model generation method of any one of claims 2 to 7, wherein the step S3 includes:

s31, calculating the index number of each DEM block in the multi-resolution DEM pyramid model and the index number of each DOM block in the multi-resolution DOM pyramid model according to the coordinates of the terrain blocks and the number of layers of the terrain blocks in the pyramid model, and taking the index numbers as main key indexes;

s32, creating an item in the database, and creating a multi-resolution DEM pyramid model data table and a multi-resolution DOM pyramid model data table in the item;

and S33, respectively storing the data of the multi-resolution DEM pyramid model and the data of the multi-resolution DOM pyramid model into a multi-resolution DEM pyramid model data table and a multi-resolution DOM pyramid model data table in a binary BLOB mode.

9. The database-based multi-resolution terrain pyramid model generation method of claim 8, wherein in step S33, the boundary data of each DEM partition is repeatedly stored in a multi-resolution DEM pyramid model data table, and a row of records is added in the multi-resolution DOM pyramid model data table for storing original size information and partition size information of DOM data.

10. A multi-resolution terrain pyramid model generation system based on a database is characterized by comprising:

a data acquisition module: acquiring original topographic data and performing format conversion to obtain DEM data and DOM data;

a model generation module: respectively generating a multi-resolution DEM pyramid model and a multi-resolution DOM pyramid model by utilizing DEM data and DOM data obtained in the data acquisition module according to the display memory limit;

a data storage module: and storing the data of the multi-resolution DEM pyramid model and the data of the multi-resolution DOM pyramid model into a database according to a preset rule.