Ship target position calculation method based on satellite image

Abstract

The invention discloses a ship target position resolving method based on satellite images. The method comprises the following steps: reading satellite position, attitude, sensor related parameters and the like at a satellite imaging moment; calculating the orbit and attitude of each imaging moment by using an interpolation algorithm; establishing a geometric mapping relation from image coordinates to ground coordinates according to the calculated orbit and attitude so as to construct a rigorous geometric model; and according to the identified ship target, obtaining the image coordinate of the ship target, substituting the image coordinate into the strict geometric model, and calculating the geographic coordinate of the ship target. The method has the advantages of high precision, quick response and wide applicability, can effectively solve the problem of positioning deviation caused by satellite imaging angles, orbit errors and earth orientation changes, and is suitable for application scenes such as vessel monitoring and marine law enforcement.

Description

Technical Field

[0001] The present invention belongs to the field of satellite remote sensing technology, and specifically relates to a method for calculating the position of a ship target based on satellite images. By using information such as the satellite orbit, attitude, and sensor parameters at the time of satellite imaging, a strict geometric imaging model is constructed to calculate the geographic coordinate position of the ship target in the image, which is applied to scenarios such as maritime monitoring and ship identification. Background Art

[0002] With the development of satellite remote sensing technology, monitoring and positioning of maritime targets (such as ships) based on satellite images has become an important application field. However, due to the geometric distortion, orbital error and complexity of earth orientation in the satellite imaging process, the accuracy of geographic coordinates obtained by relying solely on images is insufficient. Existing methods often have deficiencies in positioning accuracy and processing speed when dealing with dynamic maritime environments and rapidly changing targets. Therefore, it is of great significance to develop a high-precision ship target position solution method using a rigorous geometric model. Summary of the invention

[0003] In view of the deficiencies of the prior art, the object of the present invention is to provide a method for calculating the position of a ship target based on satellite images.

[0004] The object of the present invention is achieved through the following technical scheme: A method for calculating the position of a ship target based on satellite images, comprising the following steps:

[0005] Read the orbital data, attitude data, camera internal and external calibration parameters, time data, earth orientation parameters EOP and global digital elevation model DEM at the time of satellite image imaging; the orbital data records the spatial position of the satellite at different times, the attitude data describes the angle and direction of the satellite at different times, the camera internal and external calibration parameters are used to correct the geometric distortion of sensor imaging, the time data records the imaging time of each line of the image, the EOP describes the relevant information of the earth orientation, and the DEM provides the terrain information of the target area;

[0006] Based on the orbital data and attitude data, the satellite orbital position and satellite attitude at the imaging moment of each row in the row-time data are calculated;

[0007] Using EOP and DEM information, combined with the calculated satellite orbit position, satellite attitude and camera internal and external calibration parameters, a rigorous geometric imaging model from the image coordinate system to the ground coordinate system is established; the rigorous geometric imaging model takes into account the satellite attitude changes and ground elevation differences to ensure high-precision transformation from the image coordinate system to the ground coordinate system, thereby improving the accuracy of target position solution;

[0008] The image coordinates of the center point of the identified ship target are obtained, substituted into the above rigorous geometric imaging model, and the geographic coordinates of the ship target are calculated.

[0009] Furthermore, the satellite orbital position is calculated by a polynomial interpolation algorithm.

[0010] Furthermore, the satellite attitude is calculated by a spherical linear interpolation algorithm.

[0011] Furthermore, the rigorous geometric imaging model accurately describes the geometric relationship between image coordinates and ground coordinates through satellite imaging parameters, and the satellite imaging parameters include orbit data, attitude data, flight time data, EOP and DEM.

[0012] Furthermore, the establishment of a rigorous geometric imaging model from the image coordinate system to the ground coordinate system includes:

[0013] For the image coordinates (x i ,y i ), where x i is the image row, y i is an image sequence, and its corresponding ground coordinates (X, Y, Z) are expressed as follows:

[0014]

[0015] in, is the position vector of the GPS phase center in the WGS84 coordinate system at time t; is the transformation matrix of the satellite body coordinate system relative to the J2000 coordinate system at time t, is the transformation matrix of the J2000 coordinate system relative to the WGS84 coordinate system at time t; (Dx Dy Dz) T is the coordinate of the GPS phase center in the body coordinate system; (dx dydz) T is the offset between the origin of the camera coordinate system and the origin of the body coordinate system; m is the scale factor; f is the camera principal distance; ψ is the deviation angle of the CCD array along the track; y0 is the position corresponding to the principal visual axis, and the principal visual axis is the vertical point passing through the principal point and perpendicular to the CCD linear array; λ ccd To explore the size of the element;

[0016] Since the eccentricity vector of GPS and the offset vector of the projection center are small after canceling each other, and the line and angle elements of aerospace photogrammetry are strongly correlated, the eccentricity vector error is incorporated into the installation matrix, and formula (1.1) is simplified as follows:

[0017]

[0018] Since there is The four unknowns m and m make it impossible to establish the corresponding relationship between the image coordinates and the ground coordinates. On this basis, the earth ellipsoid equation is introduced:

[0019]

[0020] Among them, A=a+h, B=b+h, h is the elevation of the ground point, a and b represent the major and minor semi-axes of the earth ellipsoid respectively;

[0021] Assume a point (s, l) on the image, where s represents the column and l represents the row; the imaging time of the lth scanning row is t l ; Use the orbital model to interpolate t l Time track, the posture model is interpolated to t l Attitude; Assume that the elevation of the point is h; then the unknown number in the forward transformation is and m, solved by combining equations (1.1) and (1.2);

[0022] Substituting equation (1.1) into equation (1.2) and equation (1.3), X, Y, and Z are i , Y i , Z i ;

[0023]

[0024] Solve the quadratic equation of formula (1.3) with respect to m to obtain m; calculate the three-dimensional coordinates of the point in WGS84 according to formula (1.1).

[0025] The present invention also provides an electronic device, comprising a memory and a processor, wherein the memory is coupled to the processor; wherein the memory is used to store program data, and the processor is used to execute the program data to implement the method for solving the ship target position based on satellite images.

[0026] The present invention also provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the method for calculating the ship target position based on satellite images is implemented.

[0027] The beneficial effect of the present invention is that the method for calculating the position of a ship target based on satellite images provided by the present invention has the characteristics of high precision and high response speed. Through a rigorous geometric model, the method can effectively solve the positioning deviation problem caused by satellite imaging angle, orbit error and earth orientation change, and realize the rapid and accurate positioning of dynamic ship targets, which is suitable for multiple application fields such as maritime law enforcement and ship monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0029] Figure 1 is a flow chart of the present invention;

[0030] Figure 2 This is the result diagram of ship target position recognition according to the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] like Figure 1 As shown, an embodiment of the present invention provides a method for calculating the position of a ship target based on satellite images, comprising the following steps:

[0033] Step 1: Data loading.

[0034] The conventional file reading function fscanf is used to read the orbital data, attitude data, camera internal and external calibration parameters, time-of-flight data, earth orientation parameters (EOP), and global digital elevation model (DEM) of the satellite image at the time of imaging. The orbital data records the spatial position of the satellite at different times, the attitude data describes the imaging angle and direction of the satellite, the camera internal and external calibration parameters are used to correct the geometric distortion of sensor imaging, the time-of-flight data records the imaging time of each line of the satellite image, the EOP parameters describe the relevant information of the earth orientation, and the DEM provides the terrain information of the target area.

[0035] Step 2: Trajectory and pose interpolation.

[0036] The orbit and attitude data are calculated through interpolation algorithms; the orbit interpolation uses the polynomial interpolation method to calculate the specific position of the satellite in orbit at each imaging moment; the attitude interpolation uses the spherical linear interpolation method to calculate the attitude direction of the satellite during imaging. These two parameters provide basic data for the construction of subsequent geometric models.

[0037] Step 3: Build a rigorous geometric model.

[0038] Based on the interpolated orbit, attitude and other information, a rigorous geometric imaging model from the image coordinate system to the ground coordinate system is constructed. The rigorous geometric imaging model can accurately describe the geometric relationship between the pixel points in the image and the actual geographical location. The specific method is as follows:

[0039] The strict geometric imaging positioning model of the linear array push-broom optical satellite is as follows:

[0040]

[0041] in, is the position vector of the GPS phase center in the WGS84 coordinate system at time t; is the transformation matrix of the satellite body coordinate system relative to the J2000 coordinate system at time t, is the transformation matrix of the J2000 coordinate system relative to the WGS84 coordinate system at time t; (Dx Dy Dz) T is the coordinate of the GPS phase center in the body coordinate system; (dx dydz) T is the offset between the origin of the camera coordinate system and the origin of the body coordinate system; m is the scale factor; f is the camera principal distance; ψ is the CCD array along the track deviation angle; y0 is the corresponding position of the principal visual axis (the vertical point passing through the principal point perpendicular to the CCD linear array); λ ccd To detect the size of the element.

[0042] Since the GPS eccentricity vector and the offset vector of the projection center are small after canceling each other, and considering the strong correlation between the line and angle elements of aerospace photogrammetry, the eccentricity vector error can be incorporated into the installation matrix. Therefore, in practical applications, formula (1.1) can be simplified as follows:

[0043]

[0044] Since there is and m are four unknowns, it is impossible to establish a one-to-one correspondence between image coordinates and ground coordinates, so it is necessary to introduce the earth ellipsoid equation on this basis:

[0045]

[0046] Among them, A = a + h, B = b + h, h is the elevation of the ground point, a, b represent the major and minor semi-axes of the earth ellipsoid respectively. For the WGS84 ellipsoid, a = 6378137.0m, b = 6356752.3m.

[0047] Assume that at a point (s, l) on the image (s represents the column, l represents the row), the imaging time of the lth scanning row is t l . Using the orbital model to interpolate t l Time track, the posture model is interpolated to t l Assume that the elevation of this point is h. Then the unknown number in the forward transformation is only and m can be solved by combining equations (1.1) and (1.2).

[0048] Substituting equation (1.1) into equation (1.2), in equation (1.3), XYZ is X i , Y i , Z i .

[0049]

[0050] Solving the quadratic equation of formula (1.3) with respect to m will give m (the smaller one can be taken as the correct answer); then the three-dimensional coordinates of the point in WGS84 are calculated according to formula (1.1).

[0051] Step 4: Target position calculation.

[0052] According to the image coordinates of the region of interest (ROI), the image coordinates of the point are substituted into the rigorous geometric model to solve the geographic coordinates of the target. The result is as follows: Figure 2 As shown, according to Figure 2 The row and column numbers of the center point of the ROI are used to find the imaging time corresponding to the target in the satellite time data, and then the orbit and attitude interpolation are performed on the imaging time. The interpolated data is substituted into the rigorous geometric model to solve the coordinates corresponding to the WGS84 coordinate system.

[0053] It is usually difficult to know the ground elevation corresponding to the center point (s, l) of the area of ​​interest in advance. When an existing DEM is provided, a positive transformation can be performed by iterative calculation. The specific steps are as follows:

[0054] a. Assuming the elevation of (s, l) is h0, perform a positive transformation according to equations (1.1) to (1.3) to find the corresponding ground coordinates

[0055] b. Use appropriate interpolation algorithms to interpolate ground coordinates from the provided DEM The corresponding elevation is h1.

[0056] c. Update h0=h1.

[0057] d. Repeat steps ac until |h0-h1|≤r, where r is the given threshold, and output the final

[0058] In this way, the present invention can quickly and accurately obtain the geographical location of the ship target, and is suitable for real-time monitoring and target positioning.

[0059] An embodiment of the present invention also provides an electronic device, including a memory and a processor, wherein the memory is coupled to the processor; wherein the memory is used to store program data, and the processor is used to execute the program data to implement a method for solving a ship target position based on satellite images as described in the embodiment.

[0060] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the method for calculating the position of a ship target based on satellite images described in the embodiment is implemented.

[0061] The computer-readable storage medium may be an internal storage unit of any device with data processing capability described in any of the aforementioned embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be any device with data processing capability, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit of any device with data processing capability and an external storage device. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capability, and may also be used to temporarily store data that has been output or is to be output.

[0062] Those skilled in the art will readily appreciate other embodiments of the present application after considering the description and practicing the contents disclosed herein. The present application is intended to cover any variations, uses or adaptations of the present application, which follow the general principles of the present application and include common knowledge or customary technical means in the art that are not disclosed in the present application. The description and examples are intended to be exemplary only.

[0063] It should be understood that the present application is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof.

Claims

1. A method for calculating the position of a ship target based on satellite images, characterized in that: The following steps are involved: Read the orbital data, attitude data, camera internal and external calibration parameters, time data, earth orientation parameters EOP and global digital elevation model DEM at the time of satellite image imaging; the orbital data records the spatial position of the satellite at different times, the attitude data describes the angle and direction of the satellite at different times, the camera internal and external calibration parameters are used to correct the geometric distortion of sensor imaging, the time data records the imaging time of each line of the image, the EOP describes the relevant information of the earth orientation, and the DEM provides the terrain information of the target area; Based on the orbital data and attitude data, calculate the satellite orbital position and satellite attitude at the imaging moment of each row in the row-time data; Using EOP and DEM information, combined with the calculated satellite orbit position, satellite attitude and camera internal and external calibration parameters, a rigorous geometric imaging model from the image coordinate system to the ground coordinate system is established; the rigorous geometric imaging model takes into account the satellite attitude changes and ground elevation differences to ensure high-precision transformation from the image coordinate system to the ground coordinate system, thereby improving the accuracy of target position solution; The image coordinates of the center point of the identified ship target are obtained, substituted into the above rigorous geometric imaging model, and the geographic coordinates of the ship target are calculated.

2. The method for calculating the position of a ship target based on satellite images according to claim 1, characterized in that: The satellite orbital positions are calculated using a polynomial interpolation algorithm.

3. The method for calculating the ship target position based on satellite images according to claim 1, characterized in that: The satellite attitude is calculated by a spherical linear interpolation algorithm.

4. The method for calculating the position of a ship target based on satellite images according to claim 1, characterized in that: The rigorous geometric imaging model accurately describes the geometric relationship between image coordinates and ground coordinates through satellite imaging parameters, and the satellite imaging parameters include orbit data, attitude data, travel time data, EOP and DEM.

5. The method for calculating the ship target position based on satellite images according to claim 1, characterized in that: The establishment of a rigorous geometric imaging model from an image coordinate system to a ground coordinate system includes: For the image coordinates (x i ,y i ), where x i is the image row, y i is an image sequence, and its corresponding ground coordinates (X, Y, Z) are expressed as follows: in, is the position vector of the GPS phase center in the WGS84 coordinate system at time t; is the transformation matrix of the satellite body coordinate system relative to the J2000 coordinate system at time t, is the transformation matrix of the J2000 coordinate system relative to the WGS84 coordinate system at time t; (Dx Dy Dz) T is the coordinate of the GPS phase center in the body coordinate system; (dx dy dz) T is the offset between the origin of the camera coordinate system and the origin of the body coordinate system; m is the scale factor; f is the camera principal distance; ψ is the deviation angle of the CCD array along the track; y0 is the position corresponding to the principal visual axis, and the principal visual axis is the vertical point passing through the principal point and perpendicular to the CCD linear array; λ ccd To explore the size of the element; Since the eccentricity vector of GPS and the offset vector of the projection center are small after canceling each other, and the line and angle elements of aerospace photogrammetry are strongly correlated, the eccentricity vector error is incorporated into the installation matrix, and formula (1.1) is simplified as follows: Since there is The four unknowns m and m make it impossible to establish the corresponding relationship between the image coordinates and the ground coordinates. On this basis, the earth ellipsoid equation is introduced: Among them, A=a+h, B=b+h, h is the elevation of the ground point, a and b represent the major and minor semi-axes of the earth ellipsoid respectively; Assume a point (s, l) on the image, where s represents the column and l represents the row; the imaging time of the lth scanning row is t l ; Use the orbital model to interpolate t l Time track, the posture model is interpolated to t l Attitude; Assume that the elevation of the point is h; then the unknown number in the forward transformation is and m, solved by combining equations (1.1) and (1.2); Substituting equation (1.1) into equation (1.2) and equation (1.3), X, Y, and Z are i , Y i , Z i ; Solve the quadratic equation of formula (1.3) with respect to m to obtain m; calculate the three-dimensional coordinates of the point in WGS84 according to formula (1.1).

6. An electronic device comprising a memory and a processor, characterized in that: The memory is coupled to the processor; wherein the memory is used to store program data, and the processor is used to execute the program data to implement a method for solving a ship target position based on satellite images as described in any one of claims 1-5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, a method for calculating the position of a ship target based on satellite images as described in any one of claims 1 to 5 is implemented.

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