Method for calculating compass satellite visibility of urban space by using virtual panoramic occlusion diagram

Abstract

The application discloses a kind of methods for calculating city space beidou satellite visibility using virtual panoramic occlusion map, first, generate high-precision digital surface model based on point cloud;Second, calculate the initial area of high-precision digital surface model of virtual panoramic occlusion map, by constantly iterating, adaptively select the range of high-precision digital surface model used when constructing virtual panoramic occlusion map at any position in city three-dimensional space, according to the calculation of azimuth and elevation, the cylindrical virtual panoramic occlusion map is converted into hemispherical virtual panoramic occlusion map, then the map is projected into plane circumferential virtual panoramic occlusion map;Finally, according to the plane relationship diagram of plane circumferential virtual panoramic occlusion map and beidou satellite sky map, judge beidou satellite visibility.The present application improves the accuracy and resolution of existing city digital surface model;Reduce data operation amount, improve operation efficiency, improve the efficiency and accuracy of city three-dimensional space beidou satellite visibility calculation.

Description

Technical Field

[0001] The present invention belongs to the field of satellite communication technology, and in particular relates to a method for calculating the visibility of Beidou satellites in urban space by using a virtual panoramic occlusion map. Background Art

[0002] The low-altitude economy is an emerging economic form, and UAV (ultra-low-altitude) flight is a key technology for its development. The safe operation of UAVs in urban 3D spaces is a fundamental guarantee for its development. However, due to the vulnerability of Beidou satellite signals to obstruction, reflection, and scattering in complex urban environments, the Beidou positioning accuracy and reliability of UAVs are extremely unstable. This poses significant challenges to the positioning accuracy and safety of UAVs taking off and landing, and flying at (ultra-low) altitudes in complex urban environments. Furthermore, satellite visibility is a key metric for evaluating and predicting satellite positioning accuracy and reliability in complex urban environments. Therefore, Beidou satellite visibility is a crucial guarantee for the safe flight of low-altitude UAVs in these complex environments. Existing methods for obtaining Beidou satellite visibility in urban spaces mainly fall into two categories: field measurement and computational simulation. The field measurement method obtains Beidou satellite visibility through field measurements. This involves using a Beidou satellite receiver to observe Beidou satellite signals statically or dynamically, and then determining Beidou satellite visibility by combining receiver observation files and Beidou satellite ephemeris files. The computational simulation method uses Beidou satellite ephemeris and other geographic information data to calculate Beidou satellite visibility. Its applicability in complex urban environments is much higher than the actual measurement method.

[0003] Based on the data dimensions of the geographic information used, computational simulation methods are divided into methods that calculate satellite visibility using three-dimensional data and methods that calculate Beidou satellite visibility using two-dimensional data. Three-dimensional data includes point clouds (airborne and vehicle-mounted), digital elevation models, digital surface models, and three-dimensional city models; two-dimensional data includes city street view images provided by various map manufacturers. However, using this geographic information data to calculate Beidou satellite visibility has the following shortcomings:

[0004] 1. The method for calculating Beidou satellite visibility in urban spaces based on digital surface models (DSMs) analyzes whether the line connecting Beidou satellites and the points to be calculated in urban space is blocked by obstacles such as buildings. This requires sequentially traversing all regional DEMs, resulting in extremely low computational efficiency. Furthermore, the resolution of publicly available DSMs is low (typically 30 meters), making it difficult to accurately calculate Beidou satellite spatiotemporal visibility in urban 3D space.

[0005] 2. Calculating BeiDou satellite visibility in urban space based on a 3D urban model uses ray tracing to calculate BeiDou satellite signal occlusion. However, detailed 3D urban models are currently difficult to automate and require significant manpower and time. Therefore, calculating BeiDou satellite visibility in large-scale urban space is prohibitively expensive.

[0006] 3. Point clouds offer the advantage of high precision, enabling detailed calculation of urban 3D satellite visibility. However, due to occlusion between objects, vehicle-borne point clouds cannot capture the entire city's surface and feature morphology, making them only suitable for calculating satellite visibility in urban road areas. Furthermore, both vehicle-borne and airborne point clouds require large amounts of data, making it difficult to perform lightweight calculations of BeiDou satellite spatiotemporal visibility in urban 3D space.

[0007] 4. Street view imagery is widely distributed across many urban road areas, enabling lightweight and rapid calculation of satellite visibility. However, street view imagery is unavailable at any location in urban 3D space, making it impossible to use it to calculate BeiDou satellite visibility in urban 3D space. Summary of the Invention

[0008] In view of the problems existing in the above-mentioned background technology, the purpose of the present invention is to provide a method for calculating the visibility of Beidou satellites in urban space using a virtual panoramic occlusion map, so as to achieve high-precision, lightweight and fast calculation of the spatiotemporal visibility of Beidou satellites in urban three-dimensional space.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] The method for calculating Beidou satellite visibility in urban space using a virtual panoramic occlusion map comprises the following steps:

[0011] S1. Generate high-precision digital surface models based on point clouds:

[0012] Ground points are extracted from point cloud data as the basis for generating a digital surface model. The extracted ground points are divided into a certain grid structure, and elevation values ​​are assigned to each grid cell to obtain a high-precision digital surface model. This solves the problems of low resolution and poor accuracy of existing urban digital surface models, as well as low computational efficiency caused by large point cloud data volumes.

[0013] S2. Construct a virtual panoramic occlusion map based on a high-precision digital surface model:

[0014] S201. Calculate the maximum radius of the initial selection range of the high-precision digital surface model using formula (1) ,by The circular area formed as the radius of the plane is the initial area of ​​the high-precision digital surface model of the virtual panoramic occlusion map;

[0015] (1),

[0016] Where, is the maximum cutoff elevation angle of Beidou satellite, is the maximum height of the obstruction in the area to be calculated;

[0017] S202. Adaptive selection method for high-precision digital surface model area:

[0018] Calculate the height of the highest occluder in the initial area of ​​the high-precision digital surface model of the obtained virtual panoramic occlusion map The height of the point to be calculated from the ground , use formula (2) to calculate the radius of the new area :

[0019] (2),

[0020] In the new area of ​​the obtained high-precision digital surface model, formula (2) is used to iterate continuously, as the height of the calculated point from the ground increases. As the radius increases, the radius of the high-precision digital surface model area will decrease, and the range of the high-precision digital surface model will continue to shrink, until the range of the high-precision digital surface model used to construct the virtual panoramic occlusion map at any position in the urban three-dimensional space is adaptively selected;

[0021] S203, calculating the azimuth and elevation angles of all grids within the range from the center of the circle to the high-precision digital surface model based on the adaptively selected high-precision digital surface model range;

[0022] S204, sequentially arranging the calculated altitude angles corresponding to azimuth angles from 0° to 360° to obtain a cylindrical virtual panoramic occlusion map;

[0023] S205, converting the cylindrical virtual panoramic occlusion map into a hemispherical virtual panoramic occlusion map through projection, and then projecting the hemispherical virtual panoramic occlusion map into a planar circular virtual panoramic occlusion map;

[0024] By using high-precision digital surface models to construct a virtual panoramic occlusion map suitable for urban three-dimensional space, the existing problems of low algorithm efficiency and long calculation time when using digital surface models to calculate altitude and azimuth angles to determine Beidou satellite visibility are solved.

[0025] S3. Calculate Beidou satellite visibility based on the virtual panoramic occlusion map:

[0026] S301, calculating the real-time position and predicted position of the Beidou satellite in the geocentric rectangular coordinate system; using a seven-parameter conversion model to convert the Beidou satellite coordinates calculated from different ephemeris from the geocentric rectangular coordinate system to the station-centered polar coordinates with the point to be calculated as the origin;

[0027] S302, calculating the elevation angle and azimuth angle of the Beidou satellite, and converting the Beidou satellite coordinates from the station-centered rectangular coordinate system to the station-centered polar coordinate system with the point to be calculated as the origin;

[0028] S303, respectively calculating the real-time Beidou satellite coordinates using the broadcast ephemeris of the Beidou satellite and predicting the Beidou satellite position using two-row element orbit data, and drawing real-time and predicted Beidou navigation satellite sky maps;

[0029] S304: Projecting the intersection of the Beidou satellite signal and the hemispherical virtual panoramic occlusion map onto the planar circular virtual panoramic occlusion map, calculating the projection position of the projection point in the planar circular virtual panoramic occlusion map, and obtaining a planar relationship diagram between the planar circular virtual panoramic occlusion map and the Beidou satellite sky map;

[0030] S305. Determine the visibility of Beidou satellites based on the planar relationship diagram between the planar circular virtual panoramic occlusion map and the Beidou satellite sky map: when the projection position is blocked, the Beidou satellite is not visible, otherwise it is visible; calculate the visibility of all Beidou satellites at that moment and count the number of visible Beidou satellites; use the virtual panoramic occlusion map of any Beidou satellite in the city to calculate the number of visible Beidou satellites at any position in the city, and draw a three-dimensional spatial and temporal visibility map of Beidou satellites in the city.

[0031] Furthermore, in S1, the point cloud data is first processed to remove noise, outliers and duplicate points to improve the accuracy and efficiency of subsequent processing of the point cloud data; then, a cloth simulation filtering algorithm is used to extract ground points from the processed point cloud data.

[0032] Furthermore, in S2, the maximum cutoff elevation angle of the Beidou satellite The value is set to 15°.

[0033] Furthermore, in S203, in the calculation of the azimuth angle and the altitude angle, when there are multiple altitude angles for the same azimuth angle, the maximum altitude angle is retained.

[0034] Furthermore, in S205, the hemispherical virtual panoramic occlusion map is projected into a planar circular virtual panoramic occlusion map using an equidistant projection method.

[0035] Furthermore, in S301, the seven-parameter conversion model is as follows:

[0036] (3),

[0037] Where, and They are the coordinates of BeiDou satellite and station in the geocentric rectangular coordinate system. is the coordinate of the BeiDou satellite in the station-centered polar coordinate system, and are the geodetic latitude and longitude of the station, respectively.

[0038] Furthermore, in S302, the altitude angle The calculation formula is as follows:

[0039] (4),

[0040] The azimuth The calculation formula is as follows:

[0041] (5).

[0042] Furthermore, in S304, the projection position is calculated as follows:

[0043] First, according to the altitude angle Calculate the distance from the projection point to the center of the planar circular virtual panoramic occlusion map , and then according to the center distance and azimuth Calculate the projection position , the calculation formula is as follows:

[0044] (6),

[0045] (7),

[0046] Where, is the radius of the hemispherical virtual panopticon occlusion map.

[0047] Compared with the shortcomings and deficiencies of the prior art, the present invention has the following beneficial effects:

[0048] (1) Using airborne point clouds to construct high-precision and high-resolution urban digital surface models, the high-precision advantages of airborne point clouds are retained, and the problems of large data volumes and Beidou satellite visibility that exist when point clouds are directly used to calculate the visibility of Beidou satellites are solved, thereby improving the accuracy and resolution of existing urban digital surface models.

[0049] (2) By adaptively selecting the range of the digital surface model, the global data is avoided from being involved in the calculation when constructing the virtual panoramic occlusion map using the digital surface model, which reduces the amount of data calculation and improves the calculation efficiency;

[0050] (3) The method of constructing a virtual panoramic occlusion map using a high-precision digital surface model avoids the problem of digital surface models directly participating in Beidou satellite visibility calculations and solves the problem of urban three-dimensional space without panoramic image coverage;

[0051] (4) By combining the virtual panoramic occlusion map and the Beidou satellite sky map, the refined calculation of Beidou satellites in the urban three-dimensional space is realized, which improves the efficiency and accuracy of the satellite visibility calculation in the urban three-dimensional space. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Flowchart of a method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map provided by an embodiment of the present invention;

[0053] Figure 2 Schematic diagram of a method for adaptively selecting a range of a high-precision digital surface model provided by an embodiment of the present invention;

[0054] Figure 3 is a schematic diagram of calculating azimuth and elevation angles based on a high-precision digital surface model provided by an embodiment of the present invention;

[0055] Figure 4 is a cylindrical virtual panoramic occlusion map provided by an embodiment of the present invention;

[0056] Figure 5 is a planar circular virtual panoramic occlusion map provided by an embodiment of the present invention;

[0057] Figure 6 is a schematic diagram of a hemispherical isometric projection of a virtual panoramic occlusion map provided by an embodiment of the present invention;

[0058] Figure 7 It is a planar relationship diagram of a planar circular virtual panoramic occlusion image and a Beidou satellite sky image provided by an embodiment of the present invention;

[0059] Figure 8 It is a virtual panoramic occlusion map of different heights and positions of the experimental area provided by an embodiment of the present invention;

[0060] Figure 9 This is a Beidou satellite sky map used in the experiment provided in the embodiment of the present invention;

[0061] Figure 10 It is a single-point Beidou satellite visible map calculated using a virtual panoramic occlusion map in the experimental area provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0063] The present invention proposes a method for calculating the visibility of Beidou satellites in urban space using a virtual panoramic occlusion map. The flow chart is as follows: Figure 1As shown in the figure, it includes three parts: generating a high-precision digital surface model based on point cloud, constructing a virtual panoramic occlusion map based on the high-precision digital surface model, and calculating Beidou satellite visibility based on the virtual panoramic occlusion map. Each part is explained in detail below.

[0064] S1. Generate high-precision digital surface models based on point clouds:

[0065] To address the problems of low resolution and poor accuracy of existing urban digital surface models, as well as low computational efficiency due to large amount of point cloud data, the present invention proposes the following method for generating high-precision urban digital surface models using point clouds:

[0066] First, airborne LiDAR equipment is used to collect point cloud data of urban areas;

[0067] Secondly, a median filter is used to remove noise, outliers and duplicate points from the point cloud data to improve the accuracy and efficiency of subsequent point cloud processing;

[0068] Thirdly, a cloth simulation filtering algorithm is used to extract ground points from the point cloud data as the basis for generating a high-precision digital surface model;

[0069] Finally, the extracted ground points are divided according to a certain grid structure (grid and triangulated network), and an elevation value is assigned to each grid cell to obtain a high-precision digital surface model.

[0070] In response to the problems of low algorithm efficiency and long calculation time in the existing method of using digital surface models to calculate altitude and azimuth angles to judge Beidou satellite visibility, the present invention proposes the following method for calculating Beidou satellite visibility in urban three-dimensional space based on a virtual panoramic occlusion map.

[0071] S2. Construct a virtual panoramic occlusion map based on a high-precision digital surface model:

[0072] S201. Calculate the maximum radius of the initial selection range of the high-precision digital surface model using formula (1) ,by The circular area formed as the radius of the plane is the initial area of ​​the high-precision digital surface model of the virtual panoramic occlusion map;

[0073] (1),

[0074] Where, is the maximum height of the occluder in the area to be calculated, is the maximum cut-off elevation angle of BeiDou satellite. According to the measurement experience and specifications of BeiDou satellite system in cities, the maximum cut-off elevation angle of BeiDou satellite is The value of is set to 15°;

[0075] S202, propose an adaptive selection method for high-precision digital surface model areas, such as Figure 2 As shown, the height of the highest occluder is calculated in the initial area of ​​the high-precision digital surface model of the obtained virtual panoramic occlusion map. The height of the point to be calculated from the ground , the radius of the new area of ​​the high-precision digital surface model is calculated using formula (2) :

[0076] (2),

[0077] because , which significantly reduces the scope of digital surface models involved in constructing the virtual panoramic occlusion map;

[0078] In the new area of ​​the obtained high-precision digital surface model, formula (2) is used to iterate continuously, as the height of the calculated point from the ground increases. As the radius increases, the radius of the high-precision digital surface model area will decrease, and the range of the high-precision digital surface model will continue to shrink, until the range of the high-precision digital surface model used to construct the virtual panoramic occlusion map at any position in the urban three-dimensional space is adaptively selected;

[0079] S203, based on the adaptively selected high-precision digital surface model range, calculate the azimuth and elevation angles of all grids within the range from the center of the circle to the high-precision digital surface model, such as Figure 3 As shown, when there are multiple elevation angles at the same azimuth, the maximum elevation angle is retained;

[0080] S204, arranging the calculated altitude angles corresponding to the azimuth angles from 0° to 360° in sequence, and obtaining Figure 4 The cylindrical virtual panoramic occlusion map shown;

[0081] S205, converting the cylindrical virtual panoramic occlusion map into a hemispherical virtual panoramic occlusion map by projection, and then projecting the hemispherical virtual panoramic occlusion map into a planar circular virtual panoramic occlusion map by using an equidistant projection method, such as Figure 5 shown.

[0082] S3. Calculate Beidou satellite visibility based on the virtual panoramic occlusion map:

[0083] S301. Calculate the real-time and predicted positions of Beidou satellites in the geocentric rectangular coordinate system using the Beidou satellite system's broadcast ephemeris and two lines of element orbital data. Use a seven-parameter conversion model to convert the Beidou satellite coordinates calculated using different ephemeris from the geocentric rectangular coordinate system to the station-centered rectangular coordinate system with the point to be calculated as the origin. The seven-parameter conversion model is as follows:

[0084] (3),

[0085] Where, and They are the coordinates of BeiDou satellite and station in the geocentric rectangular coordinate system. is the coordinate of the BeiDou satellite in the station-centered polar coordinate system, and are the geodetic latitude and longitude of the station, respectively;

[0086] S302, use equations (4) and (5) to calculate the elevation angle of the Beidou satellite and azimuth , convert the BeiDou satellite coordinates from the geocentric rectangular coordinate system to the station-centered polar coordinate system with the point to be calculated as the origin;

[0087] (4),

[0088] (5);

[0089] S303, respectively calculating the real-time Beidou satellite coordinates using the broadcast ephemeris of the Beidou satellite and predicting the Beidou satellite position using two-line element orbit data, and drawing the real-time and predicted Beidou satellite sky maps;

[0090] S304, projecting the intersection of the BeiDou satellite signal and the hemispherical virtual panoramic occlusion map onto the plane circular virtual panoramic occlusion map, such as Figure 6 As shown, P Point is the location of the Beidou satellite receiver. O Point is the center of the virtual panoramic occlusion map of the plane circle, is the radius of the virtual panoramic occlusion map of the hemispherical surface, Q Point is the intersection of BeiDou satellite signal and hemispherical virtual panoramic occlusion map. T Point is Q The point is projected onto the virtual panoramic occlusion map of the plane circle. When the Beidou satellite elevation angle is When calculating the distance from the point T after the intersection Q is projected to the center point O of the plane circle virtual panoramic occlusion map :

[0091] (6),

[0092] Where, is the radius of the hemispherical virtual panoramic occlusion map;

[0093] According to the center distance and azimuth Calculate the projection position of the projection point T in the plane circular virtual panoramic occlusion map :

[0094] (7),

[0095] Figure 7 It is a planar relationship diagram between the planar circular virtual panoramic occlusion map and the Beidou satellite sky map. It more intuitively shows the positional relationship of the Beidou satellite positions projected onto the planar circular virtual panoramic map, providing an important reference for Beidou satellite visibility judgment;

[0096] S305, judging the visibility of Beidou satellites according to the plane relationship diagram of the plane circumference virtual panoramic occlusion map and the Beidou satellite sky map: when the projection position When there is occlusion, Beidou satellites are not visible, otherwise they are visible; by calculating the visibility of all Beidou satellites at that moment, the number of visible Beidou satellites is counted; using a virtual panoramic occlusion map of any Beidou satellite in the city, the number of visible Beidou satellites at any location in the city is calculated, and a three-dimensional space-time visibility map of Beidou satellites in the city is drawn.

[0097] To verify the effectiveness of the proposed method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map, airborne point cloud data from an experimental area with a total area of ​​approximately 1 square kilometer was collected. The airborne point cloud was preprocessed to remove noise points, and a cloth simulation filtering method was used to separate ground points from non-ground points. A high-precision digital surface model of the experimental area was established, and virtual panoramic occlusion maps were constructed using the high-precision digital surface model from three randomly selected scenes. Figure 8 These are virtual panoramic occlusion images of three random scenes at 7m, 20m and 30m above the ground. Figure 8 The first and second rows of views are scenes where buildings and trees jointly block the view. Figure 8 The third row of views shows scenes with only buildings blocking the sky. It can be seen that in both building and tree-blocked environments, the virtual panoramic occlusion map can fully describe the sky obstruction, and the sky becomes wider as the altitude increases. To create a visible Beidou satellite map of the city and better serve low-altitude reliable navigation for various devices, a Beidou satellite sky map was created using the broadcast ephemeris at 01:00 UTC on May 1, 2024. Figure 9 shown. Figure 10 This single-point Beidou satellite visibility map, calculated using a virtual panoramic occlusion map in the experimental area, can be used to create a Beidou satellite visibility map for urban 3D space. Experimental verification demonstrates that this method can calculate Beidou satellite visibility in urban 3D space with high precision and in a lightweight manner. The resulting Beidou satellite visibility map accurately reflects changes in Beidou satellite visibility within urban space, providing reliable navigation for the safe flight of unmanned aerial vehicles (UAVs) in urban 3D space and safeguarding the development of low-altitude industries.

[0098] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map, characterized in that: The following steps are involved: S1. Generate high-precision digital surface models based on point clouds: Extract ground points from point cloud data as the basis for generating digital surface models. Divide the extracted ground points into a certain grid structure and assign elevation values ​​to each grid cell to obtain a high-precision digital surface model. S2. Construct a virtual panoramic occlusion map based on a high-precision digital surface model: S201. Calculate the maximum radius of the initial selection range of the high-precision digital surface model using formula (1) ,by The circular area formed as the radius of the plane is the initial area of ​​the high-precision digital surface model of the virtual panoramic occlusion map; （1）， Where, is the maximum cutoff elevation angle of Beidou satellite, is the maximum height of the obstruction in the area to be calculated; S202. Adaptive selection method for high-precision digital surface model area: Calculate the height of the highest occluder in the initial area of ​​the high-precision digital surface model of the obtained virtual panoramic occlusion map The height of the point to be calculated from the ground , use formula (2) to calculate the radius of the new area : （2）， Formula (2) is used to continuously iterate in the obtained new area of ​​the high-precision digital surface model to obtain a continuously shrinking range of the high-precision digital surface model until the high-precision digital surface model range used for adaptively selecting any position in the urban three-dimensional space to construct a virtual panoramic occlusion map is achieved; S203, calculating the azimuth and elevation angles of all grids within the range from the center of the circle to the high-precision digital surface model based on the adaptively selected high-precision digital surface model range; S204, sequentially arranging the calculated altitude angles corresponding to azimuth angles from 0° to 360° to obtain a cylindrical virtual panoramic occlusion map; S205, converting the cylindrical virtual panoramic occlusion map into a hemispherical virtual panoramic occlusion map through projection, and then projecting the hemispherical virtual panoramic occlusion map into a planar circular virtual panoramic occlusion map; S3. Calculate Beidou satellite visibility based on the virtual panoramic occlusion map: S301, calculating the real-time position and predicted position of the Beidou satellite in the geocentric rectangular coordinate system; using a seven-parameter conversion model to convert the Beidou satellite coordinates calculated from different ephemeris from the geocentric rectangular coordinate system to the station-centered polar coordinates with the point to be calculated as the origin; S302, calculating the elevation angle and azimuth angle of the Beidou satellite, and converting the Beidou satellite coordinates from the station-centered rectangular coordinate system to the station-centered polar coordinate system with the point to be calculated as the origin; S303, respectively calculating the real-time Beidou satellite coordinates using the broadcast ephemeris of the Beidou satellite and predicting the Beidou satellite position using two-line element orbit data, and drawing the real-time and predicted Beidou satellite sky maps; S304: Projecting the intersection of the Beidou satellite signal and the hemispherical virtual panoramic occlusion map onto the planar circular virtual panoramic occlusion map, calculating the projection position of the projection point in the planar circular virtual panoramic occlusion map, and obtaining a planar relationship diagram between the planar circular virtual panoramic occlusion map and the Beidou satellite sky map; S305. Determine the visibility of Beidou satellites based on the planar relationship diagram between the planar circular virtual panoramic occlusion map and the Beidou satellite sky map: when the projection position is blocked, the Beidou satellite is not visible, otherwise it is visible; calculate the visibility of all Beidou satellites at that moment and count the number of visible Beidou satellites; use the virtual panoramic occlusion map of any Beidou satellite in the city to calculate the number of visible Beidou satellites at any position in the city, and draw a three-dimensional spatial and temporal visibility map of Beidou satellites in the city.

2. The method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map according to claim 1, wherein: In S1, the point cloud data is first processed to remove noise, outliers and duplicate points, and then the ground points are extracted from the processed point cloud data using a cloth simulation filtering algorithm.

3. The method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map according to claim 1, wherein: In S2, the maximum cutoff elevation angle of the Beidou satellite The value is set to 15°.

4. The method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map according to claim 1, wherein: In S203, in the calculation of the azimuth angle and the altitude angle, when there are multiple altitude angles for the same azimuth angle, the maximum altitude angle is retained.

5. The method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map according to claim 1, wherein: In S205 , the hemispherical virtual panoramic occlusion map is projected into a planar circular virtual panoramic occlusion map using an equidistant projection method.

6. The method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map according to claim 1, wherein: In S301, the seven-parameter conversion model is as follows: （3）， Where, and They are the coordinates of BeiDou satellite and station in the geocentric rectangular coordinate system. is the coordinate of the BeiDou satellite in the station-centered polar coordinate system, and are the geodetic latitude and longitude of the station, respectively.

7. The method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map according to claim 6, wherein: In S302, the altitude angle The calculation formula is as follows: （4）， The azimuth The calculation formula is as follows: （5）。 8. The method for calculating BeiDou satellite visibility in urban space using a virtual panoramic occlusion map according to claim 7, wherein: In S304, the projection position is calculated as follows: First, according to the altitude angle Calculate the distance from the projection point to the center of the planar circular virtual panoramic occlusion map , and then according to the center distance and azimuth Calculate the projection position , the calculation formula is as follows: （6）， （7）， Where, is the radius of the hemispherical virtual panopticon occlusion map.

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