Spherical surface equal-view-angle grid clustering method and system

Abstract

The invention provides a spherical equal-view-angle grid clustering method and system. The method comprises the following steps: generating M rows and N columns of grid angular points on a spherical area; according to the distribution range of the pixel scatter points in the along-orbit direction, M rows of grid angular point data are accumulated, a grid angular point in the middle position of M grid angular points under the satellite in the along-orbit direction is selected, and a projection plane is made; projecting M rows and N columns of grid angular points and pixel scatter points to a projection plane, forming a grid in the projection plane as a projection grid, and establishing an auxiliary grid on the projection plane; carrying out scattered point clustering on the projection pixels to an auxiliary grid; and correcting the projection pixel scatter points to the projection grid, and clustering the corresponding pixel scatter points to the corresponding spherical grid. According to the method, grid angular points and pixel scatter points are projected to a dynamically generated auxiliary plane, and then clustering is carried out. Correction measures are taken for errors between the projection plane and the earth curved surface, and the errors are well eliminated.

Description

Technical Field

[0001] The present invention relates to the field of remote sensing technology, and in particular to a spherical iso-perspective grid clustering method and system. Background Art

[0002] Satellites are equipped with multiple imaging systems that scan and image the ground in different ways. Clustering pixels from the same location, different imaging devices, different bands, and different times to fuse information and generate different data products is a common application scenario. The images of each imaging system are generally transmitted back to the ground, and then pixel clustering and information fusion are performed. With the continuous increase of image data and the limitation of satellite communication bandwidth, clustering and fusion need to be processed in real time on the satellite. The clustering algorithms of existing ground systems are often not applicable to satellite-borne embedded systems.

[0003] Since the earth's surface is a curved surface, clustering of equal-view or equal-distance grids requires multiple trigonometric and inverse trigonometric function calculations, which increases the complexity of the calculation and cannot guarantee the real-time performance of the algorithm. In addition, there will be errors between the projection plane and the earth's curved surface.

[0004] The method involved in the patent "Large-width imaging payload image remapping method and system, patent number: 202110271612.4" does not take into account the influence of the earth's curved surface. The patent "Satellite remote sensing image irregular scattered point on-board resampling processing algorithm and system, patent number: 202210086292.X" uses the information at the imaging time for pre-clustering, and the error is large. The patent "A multi-target positioning method and system, patent number: 201910659653" requires grid clustering calculation by setting anchor point signals. The patent "A distributed power group control and group adjustment control method and device based on grid clustering, patent number 202311035991" discloses a method for clustering grids rather than a method for clustering targets into grids. The paper "Density peak clustering algorithm based on grid nearest neighbor optimization" describes how to use the data after network clustering for further clustering, but does not describe how to quickly cluster targets into grids.

[0005] Patent document CN114529831A discloses an on-board resampling processing algorithm and system for irregular scattered points of satellite remote sensing images, which obtain satellite attitude parameters, satellite positioning parameters, and uncalibrated remote sensing image data values, and calculate imaging time; obtain geographical location coordinates corresponding to the pixels of remote sensing image data one by one; convert the uncalibrated remote sensing image into calibrated image data with physical meaning and dimension; record the imaging time, calibrated remote sensing data, and geographical location information in a cache; determine the required index range of the number of rows of irregular scattered points, and release the storage space of irregular scattered points that is no longer needed in the cache; determine the index range of the number of columns of irregular scattered points required for each new point; calculate the square of the spatial distance between the new point and the irregular point; screen out multiple irregular discrete points that are close to the new point; calculate the physical value corresponding to the position of the new point and output it.

[0006] However, patent document CN114529831A uses information of imaging time for pre-clustering, which results in large errors. Summary of the invention

[0007] In view of the defects in the prior art, the object of the present invention is to provide a spherical iso-perspective grid clustering method and system.

[0008] A spherical iso-perspective grid clustering method provided by the present invention comprises:

[0009] Grid corner point generation step: generate M rows and N columns of grid corner points on the spherical area;

[0010] Projection plane establishment steps: according to the distribution range of pixel scattered points in the along-track direction, accumulate M rows of grid corner point data, select the grid corner point in the middle position of the M grid corner points under the satellite in the along-track direction, and make a projection plane;

[0011] Projection step: projecting the grid corner points and pixel scattered points of the M rows and N columns onto the projection plane, forming a grid in the projection plane as a projection grid, grid corner points in the projection grid as projection grid corner points, and pixel scattered points in the projection grid as projection pixel scattered points;

[0012] Auxiliary grid establishment step: establishing an auxiliary grid on the projection plane;

[0013] Auxiliary grid clustering step: clustering the projected pixel scatter points into the auxiliary grid;

[0014] Correction steps: Correct the projected pixel scatter points to the projected grid, and cluster the corresponding pixel scatter points to the corresponding spherical grid.

[0015] Preferably, the grid corner point generating step includes: determining the total field of view angle in the vertical track direction according to the vertical track distribution range of the pixel scattered points, determining the number of grid corner points N according to the set vertical track direction, determining the angle between two adjacent grid corner points and the satellite, and generating corner point data at every set time interval Δt. In each generation, the total field of view angle, the angular spacing on both sides of the vertical track direction, and the number of grid corner points remain unchanged.

[0016] Preferably, the angle equally divides the total field of view angle;

[0017] The total field of view angle in the vertical track direction is symmetrical along both sides of the track, and the range envelops the vertical track distribution range of pixel scatter points;

[0018] The number of corner points M is an odd number, and the sub-satellite point is used as the grid corner point; N is an odd number, and N rows of grid corner points envelop the distribution range of pixel scattered points in the along-track direction.

[0019] Preferably, in the step of generating grid corner points, the N corner points of each row are on the spherical surface, and at the same time, on the cross section passing through the center of the sphere, the M cross sections corresponding to the M rows intersect on the same sphere diameter;

[0020] In M sections, the distribution pattern of N points is the same;

[0021] The M-1 angles formed by the M sections are equal, and the N-1 angles between the N corner points and the center of the sphere are equal;

[0022] Or the N-1 angles formed with a point S outside the sphere in the section are equal, the distance between point S and the first and Nth points among the N corner points is equal, and the distance between point S in different sections and the center of the sphere is equal.

[0023] Preferably, in the projection plane establishing step, the projection plane passes through the center of the sphere and is perpendicular to a line connecting the center of the sphere and the center position of the grid on the spherical surface;

[0024] The method also includes: establishing a two-dimensional coordinate system in the projection plane, wherein the along-track direction is the Y axis and the perpendicular-track direction is the horizontal axis X.

[0025] Preferably, recording the projection coordinates of the projection grid corner points and the projection pixel scattered points in the established two-dimensional coordinate system;

[0026] The steps for calculating the projection coordinates in a two-dimensional coordinate system include:

[0027] Step S3.1: In the earth-fixed coordinate system, calculate the coordinates of the unit vectors of the X-axis and Y-axis of the two-dimensional coordinate system, respectively, and record them as (x xn ,y xn ,z xn ) and (x yn ,y yn ,z yn );

[0028] Step S3.2: Projection plane projection point coordinates (x p ,y p ) is calculated using the following formula:

[0029] x p =x r0 x xn +y r0 y xn +z r0 z xn

[0030] y p =x r0 x yn +y r0 y yn +z r0 z yn

[0031] Among them, (x r0 ,y r0 ,z r0 ) are the coordinates of the point to be projected in the earth-fixed coordinate system.

[0032] Preferably, the auxiliary grid is composed of M rows and N columns of grid corner points, corresponding one-to-one with the projection grid, with the centers coinciding;

[0033] The time when the first row of grid corner points is generated is t1, and the time when the Mth row of grid corner points is generated is t2. Define t m =(t1+t2) / 2, the distance between adjacent grid corner points in the Y-axis direction of the auxiliary grid is equal to t m -Δt / 2 time and t m The distance between the subsatellite point and the projection point on the projection plane at +Δt / 2 is denoted as d;

[0034] According to the method in the grid corner point generation step, generate t m The corner point data is projected onto the auxiliary plane to form a point sequence L consisting of N points.

[0035] Preferably, the auxiliary grid clustering step includes: determining the row grid to which the pixel belongs by calculating the ratio of the Y coordinate in the projection coordinates of the projected pixel scatter point to d, and determining the column grid to which the pixel belongs by comparing the X coordinate value in the point column L.

[0036] Preferably, the correction step comprises:

[0037] Step S6.1: Divide the projection plane into two parts, upper and lower, with the point sequence L as the boundary. For the pixel scattered points in the upper part or the lower part, find the corresponding target grid according to the auxiliary grid where the pixel scattered points are located, and take out the coordinates of the corresponding upper or lower target grid corner points in the target grid;

[0038] Step S6.2: Determine whether the pixel scatter point is above or below the straight line connecting the target grid corner points. If yes, proceed to step S6.3; if not, the correction ends.

[0039] Step S6.3: After correcting the pixel scatter points to the target network directly above or directly below, execute step S6.1.

[0040] A spherical iso-perspective grid clustering system provided by the present invention comprises:

[0041] Grid corner point generation module: generates M rows and N columns of grid corner points on the spherical area;

[0042] Projection plane establishment module: According to the distribution range of pixel scattered points in the along-track direction, M rows of grid corner point data are accumulated, and the grid corner point at the middle position of the M grid corner points under the satellite in the along-track direction is selected to make a projection plane;

[0043] Projection module: Projecting the grid corner points and pixel scattered points of the M rows and N columns onto the projection plane, forming a grid in the projection plane as a projection grid, grid corner points in the projection grid as projection grid corner points, and pixel scattered points in the projection grid as projection pixel scattered points;

[0044] Auxiliary grid establishment module: establishes an auxiliary grid on the projection plane;

[0045] Auxiliary grid clustering module: clustering the projected pixel scatter points into the auxiliary grid;

[0046] Correction module: corrects the projected pixel scatter points to the projected grid, and clusters the corresponding pixel scatter points to the corresponding spherical grid.

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

[0048] 1. The present invention projects grid corner points and pixel scattered points onto a dynamically generated auxiliary plane and then performs clustering. Correction measures are taken for the error between the projection plane and the earth's curved surface, thereby eliminating the error better.

[0049] 2. The pixel clustering process of the present invention does not involve the calculation of trigonometric and inverse trigonometric functions, thus ensuring the real-time performance of the algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0051] Figure 1 It is a schematic diagram of the workflow of the present invention.

[0052] Figure 2 This is a cross-sectional relationship diagram of the corner points in the present invention.

[0053] Figure 3 It is a top view of the projection plane in the present invention. DETAILED DESCRIPTION

[0054] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0055] The spherical surface described in the present invention is a celestial spherical surface, and the satellite orbit flies along the column direction.

[0056] According to a spherical iso-perspective grid clustering method provided by the present invention, Figure 1 As shown, including:

[0057] Grid corner point generation steps: Design M rows and N columns of grid corner points on the spherical area that are applicable to the following steps. Determine the total field of view angle in the vertical track direction based on the vertical track distribution range of the pixel scatter points, and determine the angle between two adjacent corner points and the satellite based on the set number N of grid corner points in the vertical track direction. The angle divides the total field of view angle equally. Generate corner point data at set time intervals Δt. In each generation, the total field of view angle, the angles on both sides of the vertical track direction, and the number of grid corner points remain unchanged. Each row of N corner points is on the sphere, and at the same time, on the section passing through the center of the sphere, the M sections corresponding to the M rows intersect on the same sphere diameter. In the M sections, the distribution pattern of the N points is the same, such as Figure 2 As shown, × indicates grid corner points. The M-1 angles formed by M sections are equal. The N-1 angles formed by N corner points and the center of the sphere are equal; or the N-1 angles formed by a point S outside the sphere in the section are equal, and the distance between point S and the first point and the Nth point among the N corner points is equal, and the distance between S points in different sections and the center of the sphere is equal.

[0058] The total field of view angle in the vertical direction is symmetrical along both sides of the track, and the range envelops the vertical distribution range of pixel scattered points. The number of corner points M is an odd number, and the subsatellite point is used as the grid corner point. N is an odd number, and N rows of grid corner points envelop the distribution range of pixel scattered points in the direction along the track.

[0059] Steps for establishing the projection plane: The projection plane passes through the center of the sphere and is perpendicular to the line connecting the center of the sphere and the center position of the grid in the sphere. According to the distribution range of pixel scatter points in the along-track direction, M rows of grid corner point data are accumulated, and the grid corner point at the middle position of the M grid corner points under the satellite in the along-track direction is selected to make a projection plane. The projection plane is perpendicular to the line connecting the selected grid corner point and the center point of the earth. A two-dimensional coordinate system is established in the projection plane, with the along-track direction as the Y axis and the perpendicular-to-track direction as the horizontal axis X. The projection plane passes through the center of the earth, and the normal vector points to the side with the satellite. The two-dimensional coordinate system of the projection plane uses the center of the earth as the origin, the flight direction as the Y axis, and the Y axis rotated 90° clockwise as the X axis.

[0060] Projection step: Project the grid corner points of M rows and N columns onto the projection plane to form a grid in the projection plane. The grid corner points projected onto the projection plane are called projection grid corner points, the grid in the projection plane is called projection grid, and the area where the grid in the projection plane is located is called projection grid area. Project the pixel scatter points onto the projection plane, and the pixel scatter points in the projection plane are called projection pixel scatter points. M rows of grid corner points form (M-1)*(N-1) target grids, and record the coordinates of the grid corner points in the established two-dimensional coordinate system. Figure 3 As shown, the pixel scattered points are projected onto the projection plane, and the coordinates of the pixel scattered points in the established two-dimensional coordinate system are recorded. The coordinates of the pixel scattered points in the established two-dimensional coordinate system are stored in an M*N two-dimensional array, and the elements of the array are structure objects that record the two-dimensional coordinates. The steps of calculating the projection coordinates in the two-dimensional coordinate system include:

[0061] Step S3.1: In the earth-fixed coordinate system, calculate the coordinates of the unit vectors of the X-axis and Y-axis of the two-dimensional coordinate system, respectively, and record them as (x xn ,y xn ,z xn ) and (x yn ,y yn ,z yn ). Take the subsatellite point when the satellite flies through the middle of the M-row grid as the origin of the two-dimensional coordinate system, and take the direction opposite to the normal vector of the satellite orbital plane as the x-axis. Assume that the position of the satellite in the earth-fixed coordinate system at the middle of the M-row grid is (x s ,y s , z s )The normal vector of the satellite orbital plane is (x o ,y o , z o ), then take (x xn ,y xn , z xn )=-(x o ,y o , z o ), (x xn ,y xn , zxn ) is equal to (x s ,y s , z s ) Cross product (x xn ,y xn , z xn ) and then normalize.

[0062] Step S3.2: Projection plane projection point coordinates (x p ,y p ) is calculated using the following formula:

[0063] x p =x r0 x xn +y r0 y xn +z r0 z xn

[0064] y p =x r0 x yn +y r0 y yn +z r0 z yn

[0065] Among them, (x r0 ,y r0 ,z r0 ) are the coordinates of the point to be projected in the earth-fixed coordinate system.

[0066] Auxiliary grid establishment steps: establish an auxiliary grid on the projection plane, the auxiliary grid row direction side length is equal to the projection grid row direction side length near the center of the projection grid area or equal to the projection grid row direction side length at the corresponding position near the center line of the projection grid area row direction; the auxiliary grid column direction side length is equal to the projection grid column direction side length near the center of the projection grid area or equal to the projection grid column direction side length at the corresponding position near the center line of the projection grid area column direction.

[0067] The auxiliary grid consists of M rows and N columns of grid corner points, which correspond to the target grid one by one and overlap in the center. The time when the grid corner points of the first row are generated is t1, and the time when the grid corner points of the Mth row are generated is t2. Define t m =(t1+t2) / 2. The distance between all adjacent grid corner points in the Y-axis direction of the auxiliary grid is equal to t m -Δt / 2 time and t m +Δt / 2, the distance between the subsatellite point and the projection point on the projection plane is denoted as d. Generate t according to the method in the grid corner point generation step. mThe corner point data at each moment is projected onto the auxiliary plane to form a point sequence L consisting of N points. The point sequence L corresponds one-to-one to the corner point sequence of each row of the auxiliary grid, and the corresponding points have the same X coordinates. The point sequence L is stored in a one-dimensional array of length M. The array elements are structure objects that record one-dimensional coordinates.

[0068] Auxiliary grid clustering step: cluster the projected pixel scatter points to the auxiliary grid. By calculating the ratio of the Y coordinate in the projected coordinates of the projected pixel scatter points to d, determine which row of the grid the pixel belongs to, and by comparing the X coordinate values ​​in the point column L, determine which column the pixel is in. Among them, the comparison of the X coordinate values ​​in the point column L uses a binary search algorithm.

[0069] Correction step: Correct the projected pixel scatter points to the projected grid, and cluster the corresponding pixel scatter points to the corresponding spherical grid. The correction step includes:

[0070] Step S6.1: Divide the projection plane into two parts, upper and lower, with the point sequence L as the boundary. For the pixel scattered points in the upper part or the lower part, find the corresponding target grid according to the auxiliary grid where the pixel scattered points are located, and extract the coordinates of the corresponding upper or lower target grid corner points in the target grid.

[0071] Step S6.2: Determine whether the pixel scatter points are above or below the straight line connecting the target grid corner points. If yes, proceed to step S6.3; if no, the correction ends. The step of determining whether the pixel scatter points are above or below the straight line connecting the target grid corner points in the correction step includes:

[0072] Step S6.2.1: Calculate the position of the pixel scatter points using the following formula:

[0073] A=(x0-x1)(y1-x p )-(y0-y1)(x1-x p )

[0074] Among them, (x0, y0) and (x1, y1) are the pixel scatter points (x p ,y p ) Coordinates of the left and right corner points.

[0075] Step S6.2.2: Determine whether the pixel scatter point A is a negative value. If so, then (x p ,y p ) is below the line connecting (x0,y0) and (x1,y1); if not, p ,y p ) is above the line connecting (x0,y0) and (x1,y1).

[0076] Step S6.3: After correcting the pixel scatter points to the target network directly above or directly below, execute step S6.1.

[0077] The present invention also provides a spherical iso-perspective grid clustering system, which can be implemented by executing the process steps of the spherical iso-perspective grid clustering method, that is, those skilled in the art can understand the spherical iso-perspective grid clustering method as a preferred implementation of the spherical iso-perspective grid clustering system.

[0078] A spherical iso-perspective grid clustering system provided by the present invention comprises:

[0079] Grid corner point generation module: Generates M rows and N columns of grid corner points on the spherical area. The grid corner point generation module includes: determining the total field of view angle in the vertical track direction according to the vertical track distribution range of pixel scattered points, determining the number of grid corner points N according to the set vertical track direction, determining the angle between two adjacent grid corner points and the satellite, and generating corner point data every set time interval Δt. In each generation, the total field of view angle, the angle on both sides of the vertical track direction, and the number of grid corner points remain unchanged. The angle divides the total field of view angle equally. The total field of view angle in the vertical track direction is symmetrical along both sides of the track, and the range envelops the vertical track distribution range of pixel scattered points. The number of corner points M is an odd number, and the sub-satellite point is used as the grid corner point. N is an odd number, and the N rows of grid corner points envelop the distribution range of pixel scattered points in the along-track direction. The N corner points in each row of the grid corner point generation module are on the spherical surface, and at the same time, on the section passing through the center of the sphere, the M sections corresponding to the M rows intersect at the same sphere diameter. In the M sections, the distribution law of the N points is the same. The M-1 angles formed by the M sections are equal, and the N-1 angles formed by the N corner points and the center of the sphere are equal. Or the N-1 angles formed by the section and a point S outside the sphere are equal, and the distance between the S point and the first and Nth points of the N corner points is equal, and the distance between the S points in different sections and the center of the sphere is equal.

[0080] Projection plane establishment module: According to the distribution range of pixel scattered points in the along-track direction, M rows of grid corner point data are accumulated, and the grid corner point at the middle position of the M grid corner points under the satellite in the along-track direction is selected to make a projection plane. The projection plane in the projection plane establishment module passes through the center of the sphere and is perpendicular to the line connecting the center of the sphere and the center position of the grid in the spherical surface. It also includes: establishing a two-dimensional coordinate system in the projection plane, with the along-track direction as the Y axis and the perpendicular track direction as the horizontal axis X.

[0081] Projection module: Project the grid corner points and pixel scattered points of the M rows and N columns onto the projection plane, and the grid in the projection plane is called the projection grid, the grid corner points in the projection grid are called the projection grid corner points, and the pixel scattered points in the projection grid are called the projection pixel scattered points. Record the projection coordinates of the projection grid corner points and the projection pixel scattered points in the established two-dimensional coordinate system. The projection coordinate calculation module in the two-dimensional coordinate system includes:

[0082] Module M3.1: In the Earth-fixed coordinate system, calculate the coordinates of the unit vectors of the X-axis and Y-axis of the two-dimensional coordinate system, respectively, denoted as (x xn ,y xn ,z xn ) and (x yn ,y yn ,z yn ).

[0083] Module M3.2: Projection plane projection point coordinates (x p ,y p ) is calculated using the following formula:

[0084] x p =x r0 x xn +y r0 y xn +z r0 z xn

[0085] y p =x r0 x yn +y r0 y yn +z r0 z yn

[0086] Among them, (x r0 ,y r0 ,z r0 ) are the coordinates of the point to be projected in the earth-fixed coordinate system.

[0087] Auxiliary grid establishment module: establish an auxiliary grid on the projection plane. The auxiliary grid consists of M rows and N columns of grid corner points, which correspond to the projection grid one by one and have the same center. The time when the first row of grid corner points is generated is t1, and the time when the Mth row of grid corner points is generated is t2. Define t m =(t1+t2) / 2, the distance between adjacent grid corner points in the Y-axis direction of the auxiliary grid is equal to t m -Δt / 2 time and t m +Δt / 2, the distance between the subsatellite point and the projection point on the projection plane is denoted as d. Generate t according to the method in the grid corner point generation module. m The corner point data is projected onto the auxiliary plane to form a point sequence L consisting of N points.

[0088] Auxiliary grid clustering module: clustering the projected pixel scatter points to the auxiliary grid. The auxiliary grid clustering module includes: determining the row grid to which the pixel belongs by calculating the ratio of the Y coordinate in the projected coordinates of the projected pixel scatter points to d, and determining the column grid to which the pixel belongs by comparing the X coordinate value in the point column L.

[0089] Correction module: corrects the projected pixel scatter points to the projected grid, and clusters the corresponding pixel scatter points to the corresponding spherical grid. The correction module includes:

[0090] Module M6.1: Divide the projection plane into two parts, upper and lower, with the point sequence L as the boundary. For the pixel scatter points in the upper or lower part, find the corresponding target grid according to the auxiliary grid where the pixel scatter points are located, and take out the coordinates of the corresponding upper or lower target grid corner points in the target grid.

[0091] Module M6.2: Determine whether the pixel scatter point is above or below the straight line connecting the target grid corner points, if yes, proceed to module M6.3. If no, the correction ends.

[0092] Module M6.3: After correcting the pixel scatter points to the target network directly above or directly below, execute module M6.1.

[0093] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0094] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A spherical iso-perspective grid clustering method, characterized in that: include: Grid corner point generation step: generate M rows and N columns of grid corner points on the spherical area; Projection plane establishment steps: according to the distribution range of pixel scattered points in the along-track direction, accumulate M rows of grid corner point data, select the grid corner point in the middle position of the M grid corner points under the satellite in the along-track direction, and make a projection plane; Projection step: projecting the grid corner points and pixel scattered points of the M rows and N columns onto the projection plane, forming a grid in the projection plane as a projection grid, grid corner points in the projection grid as projection grid corner points, and pixel scattered points in the projection grid as projection pixel scattered points; Auxiliary grid establishment step: establishing an auxiliary grid on the projection plane; Auxiliary grid clustering step: clustering the projected pixel scatter points into the auxiliary grid; Correction steps: Correct the projected pixel scatter points to the projected grid, and cluster the corresponding pixel scatter points to the corresponding spherical grid.

2. The spherical iso-perspective grid clustering method according to claim 1, characterized in that: The grid corner point generation step includes: determining the total field of view angle in the vertical track direction according to the vertical track distribution range of pixel scattered points, determining the number of grid corner points N according to the set vertical track direction, determining the angle between two adjacent grid corner points and the satellite, and generating corner point data at a set time interval Δt. In each generation, the total field of view angle, the angular spacing on both sides of the vertical track direction, and the number of grid corner points remain unchanged.

3. The spherical iso-perspective grid clustering method according to claim 2, characterized in that: The angle equally divides the total field of view; The total field of view angle in the vertical track direction is symmetrical along both sides of the track, and the range envelops the vertical track distribution range of pixel scatter points; The number of corner points M is an odd number, and the sub-satellite point is used as the grid corner point; N is an odd number, and N rows of grid corner points envelop the distribution range of pixel scattered points in the along-track direction.

4. The spherical iso-perspective grid clustering method according to claim 1, characterized in that: In the step of generating grid corner points, the N corner points of each row are on the spherical surface, and at the same time, on the cross section passing through the center of the sphere, the M cross sections corresponding to the M rows intersect on the same sphere diameter; In M sections, the distribution pattern of N points is the same; The M-1 angles formed by the M sections are equal, and the N-1 angles between the N corner points and the center of the sphere are equal; Or the N-1 angles formed with a point S outside the sphere in the section are equal, the distance between point S and the first and Nth points among the N corner points is equal, and the distance between point S in different sections and the center of the sphere is equal.

5. The spherical iso-perspective grid clustering method according to claim 1, characterized in that: In the projection plane establishment step, the projection plane passes through the center of the sphere and is perpendicular to the line connecting the center of the sphere and the center position of the grid on the spherical surface; The method also includes: establishing a two-dimensional coordinate system in the projection plane, wherein the along-track direction is the Y axis and the perpendicular-track direction is the horizontal axis X.

6. The spherical iso-perspective grid clustering method according to claim 5, characterized in that: Record the projection coordinates of the projection grid corner points and the projection pixel scattered points in the established two-dimensional coordinate system; The steps for calculating the projection coordinates in a two-dimensional coordinate system include: Step S3.1: In the earth-fixed coordinate system, calculate the coordinates of the unit vectors of the X-axis and Y-axis of the two-dimensional coordinate system, respectively, and record them as (x xn ,y xn ,z xn ) and (x yn ,y yn ,z yn ); Step S3.2: Projection plane projection point coordinates (x p ,y p ) is calculated using the following formula: x p =x r0 x xn +y r0 y xn +z r0 z xn and p =x r0 x yn +y r0 and yn +z r0 z yn Among them, (x r0 ,y r0 ,z r0 ) are the coordinates of the point to be projected in the earth-fixed coordinate system.

7. The spherical iso-perspective grid clustering method according to claim 1, characterized in that: The auxiliary grid is composed of M rows and N columns of grid corner points, which correspond to the projection grid one by one and have the same center. The time when the first row of grid corner points is generated is t1, and the time when the Mth row of grid corner points is generated is t2. Define t m =(t1+t2) / 2, the distance between adjacent grid corner points in the Y-axis direction of the auxiliary grid is equal to t m -Δt / 2 time and t m The distance between the subsatellite point and the projection point on the projection plane at +Δt / 2 is denoted as d; According to the method in the grid corner point generation step, generate t m The corner point data is projected onto the auxiliary plane to form a point sequence L consisting of N points.

8. The spherical iso-perspective grid clustering method according to claim 7, characterized in that: The auxiliary grid clustering step includes: determining the row grid to which the pixel belongs by calculating the ratio of the Y coordinate in the projection coordinates of the projected pixel scatter points to d, and determining the column grid to which the pixel belongs by comparing the X coordinate values ​​in the point column L.

9. The spherical iso-perspective grid clustering method according to claim 1, characterized in that: The correction steps include: Step S6.1: Divide the projection plane into two parts, upper and lower, with the point sequence L as the boundary. For the pixel scattered points in the upper part or the lower part, find the corresponding target grid according to the auxiliary grid where the pixel scattered points are located, and take out the coordinates of the corresponding upper or lower target grid corner points in the target grid; Step S6.2: Determine whether the pixel scatter point is above or below the straight line connecting the target grid corner points. If yes, proceed to step S6.3; if not, the correction ends. Step S6.3: After correcting the pixel scatter points to the target network directly above or directly below, execute step S6.

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10. A spherical iso-perspective grid clustering system, characterized in that: include: Grid corner point generation module: generates M rows and N columns of grid corner points on the spherical area; Projection plane establishment module: According to the distribution range of pixel scattered points in the along-track direction, M rows of grid corner point data are accumulated, and the grid corner point at the middle position of the M grid corner points under the satellite in the along-track direction is selected to make a projection plane; Projection module: Projecting the grid corner points and pixel scattered points of the M rows and N columns onto the projection plane, forming a grid in the projection plane as a projection grid, grid corner points in the projection grid as projection grid corner points, and pixel scattered points in the projection grid as projection pixel scattered points; Auxiliary grid establishment module: establishes an auxiliary grid on the projection plane; Auxiliary grid clustering module: clustering the projected pixel scatter points into the auxiliary grid; Correction module: corrects the projected pixel scatter points to the projected grid, and clusters the corresponding pixel scatter points to the corresponding spherical grid.

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