On-orbit Geometric Positioning Method and System for High-orbit Large-area Array Cameras Based on the Earth's Outline

Abstract

The present invention discloses an on-orbit geometric positioning method and system for a high-orbit large area array camera based on the earth's contour, which relates to the field of space remote sensing technology. An on-orbit geometric model of the high-orbit large area array camera is established; the earth's contour within the observation field of the model camera is extracted to obtain the coordinates of the earth's contour; based on the coordinates of the earth's contour, the center point of the earth's contour is obtained; the camera attitude angle is calculated according to the position of the center point of the earth's contour and the center of the earth; the polar coordinates of the remote sensing image in the LOS projection plane are calculated using the azimuth angle and elevation angle of the camera attitude angle, and the projection of the remote sensing image during reference map projection matching is obtained using the rotation angle of the camera attitude angle, and the transformation of the image point in the remote sensing image to the geocentric fixed system coordinates of the corresponding earth surface point is carried out to achieve on-orbit geometric positioning. The on-orbit geometric positioning method and system for a high-orbit large area array camera based on the earth's contour provided by the present invention solve the technical problems that factors such as clouds, the number and distribution of control points have a great influence on the positioning accuracy.

Description

Technical Field

[0001] The present invention relates to the field of space remote sensing technology, and more particularly to a high-precision on-orbit geometric positioning method and system for a high-orbit large-area array camera based on the earth's contour. Background Art

[0002] At present, affected by vibrations, shocks, and thermal environment changes during launch and on-orbit operation, the geometric positioning model of a remotely sensed camera calibrated on the ground will deviate, affecting the geometric accuracy of the image. In practical applications, recalibration must be carried out. Currently, ground control points (GCPs) or stars are usually used as references to construct a geometric calibration model, and the calibration parameter solution is achieved according to the attitude and orbit parameters provided by the satellite orbit determination and attitude measurement system. Affected by the measurement accuracy of the orbit determination and attitude measurement system, the acquisition accuracy of the reference information, etc., the on-orbit geometric positioning method usually relies on the ground calibration field. By using the ground geometric calibration field images taken by the remotely sensed camera during on-orbit operation, high-precision GCPs are extracted to achieve the solution of the positioning model. This method is mostly applied to high-precision mapping satellites.

[0003] However, since establishing a ground calibration field requires a large amount of manpower and material resources and cannot be deployed globally, it does not meet the requirements of on-orbit positioning in any scenario. Moreover, the method based on the ground calibration field highly depends on the high-precision ground calibration field reference information and the number of manually selected ground control points, usually with low efficiency and instability. To reduce the dependence on the calibration field and improve the solution efficiency, the method of automatically extracting GCPs based on geographic reference for on-orbit positioning has been widely used. A large number of GCPs are extracted by matching the digital orthophoto map and the digital elevation model with the on-orbit images respectively. Although the above GCP extraction method helps with automatic calibration, the geometric positioning accuracy of the image largely depends on the cloud coverage rate in the image and the distribution of GCPs. However, since cloud cover is difficult to predict and some features will change greatly compared with the reference image, it is impossible to obtain available remotely sensed images in real time, bringing great difficulties to the immediate calibration of emergency positioning requirements. In addition, the on-orbit geometric positioning method based on stars regards stars as a kind of control points, similar to the method based on ground control points, which requires obtaining a large amount of high-precision star position information as a reference. However, since the number of observable stars in the camera's field of view is limited, when there are only a few or even one star, the number of control points is not enough to solve the calibration parameters, limiting the use of this method.

[0004] Therefore, how to avoid the influence of factors such as clouds, the number of control points, and distribution on the positioning accuracy is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides an on-orbit geometric positioning method for a high-orbit large-area array camera based on the earth's contour, which uses the earth's contour to calculate the camera attitude parameters and realizes high-precision geometric positioning of the camera.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] An on-orbit geometric positioning method for a high-orbit large-area array camera based on the earth's contour includes the following steps:

[0008] Step 1: Establish an on-orbit geometric model for the high-orbit large-area array camera;

[0009] Step 2: According to the on-orbit geometric model of the high-orbit large-area array camera established in Step 1, extract the earth's contour within the observation field of view of the high-orbit large-area array camera, establish an image coordinate system and a focal plane coordinate system, and extract the image coordinates of the earth's contour points;

[0010] Step 3: Use the image coordinates of the earth's contour points in Step 2 to calculate the center point of the earth's contour;

[0011] Step 4: Establish a camera coordinate system O c -X c Y c Z c , and calculate the camera attitude angles according to the center point of the earth's contour and the position of the earth's center in Step 3;

[0012] Step 5: Calculate the polar coordinates of the remote sensing image in the LOS projection plane through the azimuth angle and elevation angle in the camera attitude angle parameters in Step 4; use the rotation angle in the camera attitude angle parameters to obtain the projection of the remote sensing image when matching with the reference map projection, and perform the transformation of the image point in the remote sensing image to the geocentric fixed system coordinates of the corresponding earth surface point to achieve on-orbit geometric positioning.

[0013] The beneficial effects of adopting the above method are as follows: By determining the camera attitude information through the earth's contour and solving the positioning model, the problem that the positioning accuracy of the existing method is limited by the measurement accuracy of the orbit determination and attitude measurement system is solved, and high-precision geometric positioning of the high-orbit large-area array camera is realized.

[0014] Preferably, Step 2 is specifically implemented according to the following steps: For the remote sensing image captured by the large-area array camera, use the Sobel operator to detect and extract the earth's contour. The Sobel operator convolution kernel is:

[0015]

[0016] I represents the original image, G u , G v represents the image gray values after horizontal and vertical edge detection. According to the above formula, obtain the image coordinates (u i , vi )。

[0017] Preferably, step 3 is specifically implemented according to the following steps: According to the image coordinates of N earth contour points, the position coordinates (u O ,, v O ,) of the image point O' corresponding to the imaging of the camera on the center of the earth are calculated by using the least square method, and the formula is as follows:

[0018]

[0019] (u i , v i ) are the image coordinates of the earth contour points, and R is the calculated radius of the center of the circle.

[0020] Preferably, step 4 is specifically implemented according to the following steps:

[0021] Step 4.1: The camera attitude angles include the azimuth angle θ and the elevation angle φ, and (θ, φ) are calculated by the following formula:

[0022]

[0023] (u O’ , v O’ ) are the position coordinates of the image point O' corresponding to the imaging of the camera on the center of the earth, (u0, v0) are the coordinates of the principal point of the camera in the image coordinate system, dx and dy are the pixel sizes in the x-axis and y y-axis directions respectively, and f is the focal length of the camera:

[0024] Step 4.2: The camera attitude angle also includes the rotation angle ψ. In the camera coordinate system O c -X c Y c Z c , LOS O , is the observation vector of the camera on the center of the earth. A plane perpendicular to LOS O , is constructed, and this plane is the LOS projection plane; A polar coordinate system is established in the LOS projection plane, O LOS is the pole, and Ψ is the polar axis. The remote sensing image and the reference map are respectively transformed into the polar coordinate system through the projection matrix. In the LOS projection plane, the projection of the remote sensing image is translated along the Ψ axis, and the translated projection of the remote sensing image is matched with the projection of the reference map; When the two are matched, the angle increased by the translation of the projection of the remote sensing image along the Ψ axis is the rotation angle ψ.

[0025] The beneficial effect of adopting the above method is that the remote sensing image coordinates (u, v) can be converted to polar coordinates (r, Ψ) img , that is, the projection of the remote sensing image in the polar coordinate system of the LOS projection plane; The geocentric fixed system coordinates (X, Y, Z) of the reference map are converted to polar coordinates (r, Ψ)map , namely the reference map projection in the polar coordinate system of the LOS projection plane.

[0026] Step 4.2.1: The projection matrix from the polar coordinates (r, Ψ) in the LOS projection plane to the image coordinate system (u, v) is calculated by the following formula:

[0027]

[0028] are respectively the rotation matrices of the LOS projection plane rotating around the X c , Y c , Z c axis;

[0029] Step 4.2.2: θ E is the geocentric angle corresponding to the point on the earth's surface, and is calculated by the following formula:

[0030]

[0031] is the distance between the camera center Oc and the point on the earth's surface, θ s = arctan(r);

[0032] Step 4.2.3: The projection matrix from the polar coordinates in the LOS projection plane to the reference map is obtained through the following formula:

[0033]

[0034] (X, Y, Z), (lon, lat, R) are respectively the coordinates of the point on the earth's surface in the geocentric fixed coordinate system and the geodetic coordinate system, R is the radius of the earth, the Xce axis, the Yce axis, and the Zce axis are respectively the three-axis directions of the geocentric fixed coordinate system. The Xce axis is located in the equatorial plane and points to the intersection of the Greenwich meridian and the equator. The Yce axis is located in the equatorial plane and is perpendicular to the Xce axis. The Zce axis is perpendicular to the equatorial plane and points to the north celestial pole, R Xce (·), R Yce (·), R Zce (·) are respectively the rotation matrices of the LOS projection plane rotating around the Xce, Yce, and Zce axes.

[0035] To achieve the above object, the present invention also provides a high-orbit large-area array camera on-orbit geometric positioning system based on the earth's contour, including:

[0036] A model construction module for establishing an on-orbit geometric model of a high-orbit large-area array camera;

[0037] A contour coordinate extraction module for extracting the earth's contour within the observation field of view of the high-orbit large-area array camera, establishing an image coordinate system and a focal plane coordinate system, and extracting the image coordinates of the earth's contour points;

[0038] The contour center point calculation module establishes a camera coordinate system O c -X c Y c Z c and calculates the center point of the earth's contour;

[0039] The attitude angle determination module calculates the camera attitude angle according to the position of the center point of the earth's contour and the center of the earth;

[0040] The on-orbit geometric positioning module calculates the polar coordinates of the remote sensing image in the LOS projection plane through the azimuth angle and elevation angle in the camera attitude angle parameters; using the rotation angle, the projection of the remote sensing image when matching the reference map projection is obtained, and the transformation of the image point in the remote sensing image to the geocentric fixed system coordinates of the corresponding earth surface point is carried out to realize on-orbit geometric positioning.

[0041] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a method and system for on-orbit geometric positioning of a high-orbit large area array camera based on the earth's contour. The camera attitude information is determined by the earth's contour constructed by the model construction module, the image coordinates of the earth's contour points are extracted by the contour coordinate extraction module, the center point of the earth's contour is calculated by the contour center point calculation module, the camera attitude angle is calculated by the attitude angle determination module, and the on-orbit geometric positioning module establishes a polar coordinate system in the LOS projection plane to transform the remote sensing image and the reference map into the polar coordinate system through the projection matrix respectively, and solves the positioning model, solving the problem that the positioning accuracy of the existing method is limited by the measurement accuracy of the orbit determination and attitude measurement system, avoiding the limitations of factors such as cloud coverage and the number of stars, and realizing high-precision geometric positioning of the high-orbit large area array camera. Description of the Drawings

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0043] Figure 1 The drawings are schematic diagrams of the observation field model of the high-orbit large area array camera.

[0044] Figure 2 The drawings are schematic diagrams for solving the azimuth angle and rotation angle of the high-orbit large area array camera.

[0045] Figure 3 The drawings are schematic diagrams for solving the rotation angle of the high-orbit large area array camera. Detailed Embodiments

[0046] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] An embodiment of the present invention discloses a method for on-orbit geometric positioning of a high-orbit large-area array camera based on the earth's contour, as Figure 1 shown, including the following steps:

[0048] Step 1: Establish an on-orbit geometric model of the high-orbit large-area array camera;

[0049] Step 2: According to the on-orbit geometric model of the high-orbit large-area array camera established in Step 1, extract the earth's contour within the observation field of view of the high-orbit large-area array camera, establish an image coordinate system and a focal plane coordinate system, and extract the image coordinates of the earth's contour points;

[0050] Step 3: Use the image coordinates of the earth's contour points in Step 2 to calculate the center point of the earth's contour;

[0051] Step 4: Establish a camera coordinate system O c -X c Y c Z c , and calculate the camera attitude angle according to the center point of the earth's contour and the position of the earth's center of the sphere in Step 3;

[0052] Step 5: Calculate the polar coordinates of the remote sensing image in the LOS projection plane through the azimuth angle and elevation angle in the camera attitude angle parameters in Step 4; use the rotation angle in the camera attitude angle parameters to obtain the projection of the remote sensing image when matching with the reference map projection, and perform the transformation of the image point in the remote sensing image to the geocentric fixed system coordinates of the corresponding earth surface point to achieve on-orbit geometric positioning.

[0053] In a specific embodiment, taking a geosynchronous orbit satellite as an example, the orbit height is about 36,000 km, and the high-orbit large-area array camera can achieve earth exploration. The camera's field of view includes the full disk image of the earth and the earth's contour. Among them, the camera in the present invention can be a single-line array, double-line array, or triple-line array digital camera.

[0054] In a specific embodiment, for the remote sensing image taken by the large-area array camera in Step 2, the Sobel operator is used to detect and extract the earth's contour. The Sobel operator convolution kernel is:

[0055]

[0056] where I represents the original image, G u , G vRepresents the grayscale value of the image after horizontal and vertical edge detection. Obtain the image coordinates (u i , v i ) of N earth contour points according to the above formula.

[0057] In a specific embodiment, the obtained remote sensing image can be an analog image, and it must be subjected to A / D conversion through means such as an image scanner before being processed by a computer.

[0058] In a specific embodiment, step 3 further includes calculating the image point O corresponding to the imaging of the camera on the center of the earth using the least squares method based on the image coordinates of N earth contour points, and the position coordinates are (u O’ , v O’ ), and the formula is as follows:

[0059]

[0060] Among them, (u i , v i ) are the image coordinates of the earth contour points, and R is the calculated radius of the center of the circle.

[0061] In a specific embodiment, as Figure 2 shown, the camera attitude angles (θ, φ, ψ) are defined as follows: In the camera coordinate system O c -X c Y c Z c ), LOS O’ is the observation vector of the camera on the center of the earth. The azimuth angle θ is the angle between the projection of LOS 0’ on the X c O c Z c plane and the -Z c axis; the elevation angle φ is the angle between LOS O’ and the X c O c Z c plane; the rotation angle ψ refers to the angle of rotation of the camera around LOS O’ , and it is the angle between two planes (the plane formed by the Y c axis and LOS0 and the plane formed by the earth Z axis and LOS o’ ).

[0062] In a specific embodiment, step 4 further includes:

[0063] Step 4.1: The camera attitude angles include the azimuth angle θ and the elevation angle φ, and (θ, φ) are calculated by the following formula:

[0064]

[0065] Among them, (uO’ , v O’ ) is the position coordinate of the image point O' corresponding to the camera imaging the center of the earth, (u0, v0) is the coordinate of the camera principal point in the image coordinate system, dx and dy are the pixel sizes in the x-axis and y-axis directions respectively, and f is the camera focal length:

[0066] Step 4.2: The camera attitude angle also includes the rotation angle ψ. In the camera coordinate system O c -X c Y c Z c , LOS 0’ is the observation vector of the camera to the center of the earth. Construct a plane perpendicular to LOS 0’ . This plane is the LOS projection plane; establish a polar coordinate system in the LOS projection plane, O LOS is the pole, Ψ is the polar axis. Transform the remote sensing image and the reference map into the polar coordinate system through the projection matrix respectively. Translate the projection of the remote sensing image along the Ψ axis in the LOS projection plane, and match the translated projection of the remote sensing image with the projection of the reference map; when the two match, the increased angle of the translation of the projection of the remote sensing image along the Ψ axis is the rotation angle ψ.

[0067] In a specific embodiment, based on the land and ocean area recognition, the area matching method is adopted to realize the matching of the projection of the remote sensing image and the projection of the reference map in the polar coordinate system of the LOS projection plane.

[0068] In a specific embodiment, as Figure 3 shown, Step 4.2 also includes:

[0069] Construct a plane perpendicular to LOS O’ , and at a distance of 1 from the camera center O c , that is, the LOS projection plane.

[0070] Step 4.2.1: The projection matrix from the polar coordinates (r, Ψ) in the LOS projection plane to the image coordinates (u, v) is calculated by the following formula:

[0071]

[0072] are the rotation matrices of the LOS projection plane rotating around the X c , Y c , Z c axis respectively. Among them, according to the above formula, the remote sensing image coordinates (u, v) can be converted to the polar coordinates (r, Ψ) img , that is, the projection of the remote sensing image in the polar coordinate system of the LOS projection plane.

[0073] Step 4.2.2: θ E is the geocentric angle corresponding to the point on the earth's surface and is calculated by the following formula:

[0074]

[0075] is the distance between the camera center Oc and the point on the earth's surface, θ s = arctan(r). Among them, according to the above analysis, the geocentric fixed system coordinates (X, Y, Z) of the reference map can be converted to polar coordinates (r, Ψ) map , that is, the reference map projection in the polar coordinate system of the LOS projection plane.

[0076] Step 4.2.3: The projection matrix from the polar coordinates of the LOS projection plane to the reference map is obtained through the following formula:

[0077]

[0078] (X, Y, Z) and (lon, lat, R) are the coordinates of the point on the earth's surface in the geocentric fixed coordinate system and the geodetic coordinate system respectively, R is the radius of the earth, the Xce axis, the Yce axis, and the Zce axis are the three axes of the geocentric fixed coordinate system respectively. The Xce axis is located in the equatorial plane and points to the intersection of the Greenwich meridian and the equator. The Yce axis is located in the equatorial plane and is perpendicular to the Xce axis. The Zce axis is perpendicular to the equatorial plane and points to the north celestial pole, R Xce (·), R Yce (·), R Zce (·) are the rotation matrices of the LOS projection plane rotating around the Xce, Yce, and Zce axes respectively.

[0079] In a specific embodiment, step 5 includes: Based on formula (4) in step 4.2.1, the polar coordinates (r, Ψ) of the remote sensing image (u, v) in the LOS projection plane can be calculated using the attitude parameters (θ, φ) img . Using the rotation angle ψ, the projection of the remote sensing image when it matches the reference map projection can be obtained, that is, (r, Ψ + ψ) img =(r, Ψ) map . Then, according to the reference map and the reference map projection (r, Ψ) in the polar coordinate system obtained by the calculation in step 4.2.2 map , the polar coordinates (r, Ψ + ψ) of the image point in the LOS projection plane can be calculated img . The geocentric fixed system coordinates (X, Y, Z) of the corresponding point on the earth's surface can be obtained, and thus the transformation from the image point (u, v) in the remote sensing image to the geocentric fixed system coordinates (X, Y, Z) of the corresponding point on the earth's surface can be completed, realizing on-orbit geometric positioning.

[0080] In a specific embodiment, a high-orbit large-area array camera on-orbit geometric positioning system based on the earth's contour is provided, including:

[0081] A model construction module that establishes an on-orbit geometric model of a high-orbit large area array camera;

[0082] A contour coordinate extraction module that extracts the Earth's contour within the observation field of view of the high-orbit large area array camera, establishes an image coordinate system and a focal plane coordinate system, and extracts the image coordinates of the Earth's contour points;

[0083] A contour center point calculation module that establishes a camera coordinate system O c -X c Y c Z c , and calculates the center point of the Earth's contour:

[0084] An attitude angle determination module that calculates the camera attitude angle based on the position of the center point of the Earth's contour and the center of the Earth;

[0085] An on-orbit geometric positioning module that calculates the polar coordinates of the remote sensing image in the LOS projection plane through the azimuth angle and elevation angle in the camera attitude angle parameters; using the rotation angle, the projection of the remote sensing image when matching the reference map projection is obtained, and the transformation of the image point in the remote sensing image to the geocentric fixed system coordinates of the corresponding Earth surface point is performed to achieve on-orbit geometric positioning.

[0086] The on-orbit geometric positioning method and system of a high-orbit large area array camera based on the Earth's contour provided by the present invention determines the camera attitude information based on the Earth's contour, solves the positioning model, solves the problem that the positioning accuracy of the existing method is limited by the measurement accuracy of the orbit determination and attitude measurement system, avoids the limitations of factors such as cloud cover and the number of stars in the prior art, and realizes high-precision geometric positioning of the high-orbit large area array camera.

[0087] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0088] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for on-orbit geometric positioning of a high-orbit large-area array camera based on the Earth's contour, characterized in that The method includes: Step 1: Establish an on-orbit geometric model of a high-orbit large area array camera; Step 2: According to the on-orbit geometric model of the high-orbit large area array camera established in Step 1, extract the Earth's contour within the observation field of view of the high-orbit large area array camera, establish an image coordinate system and a focal plane coordinate system, and extract the image coordinates of the Earth's contour points; Step 3: Calculate the center point of the Earth's contour using the image coordinates of the Earth's contour points in Step 2; Step 4: Establish the camera coordinate system O c -X c Y c Z c , and calculate the camera attitude angle according to the center point of the earth's contour and the position of the earth's center of the sphere described in Step 3; Step 5: Calculate the polar coordinates of the remote sensing image in the LOS projection plane through the azimuth and elevation angles in the camera attitude angle parameters in Step 4; Use the rotation angle in the camera attitude angle parameters to obtain the projection of the remote sensing image when it matches the reference map projection, and perform the transformation of the image points in the remote sensing image to the geocentric fixed system coordinates of the corresponding Earth surface points to achieve on-orbit geometric positioning; In Step 2, for the remote sensing image captured by the large area array camera, the Sobel operator is used to detect and extract the Earth's contour. The Sobel operator convolution kernel is: I represents the original image, G u ,G v represents the image gray value after horizontal and vertical edge detection. According to the above formula (1), the image coordinates (u i , v i ) of N earth contour points are obtained; In step 3, according to the image coordinates of N earth contour points, the image point O corresponding to the imaging of the earth's center of the sphere by the camera is calculated using the least squares method ， The position coordinates (u O ,, v O ,), and the formula is as follows: (u i , v i ) are the image coordinates of the Earth contour points, and R is the calculated radius of the center of the circle; Step 4 includes: Step 4.1: The camera attitude angles include the azimuth angle θ and the elevation angle φ, and (θ, φ) are calculated by the following formula (3): (u O’ , v O’ ) is the position coordinate of the image point O' corresponding to the imaging of the camera on the center of the earth, (u0, v0) is the coordinate of the principal point of the camera in the image coordinate system, dx and dy are the pixel sizes in the x-axis and y-axis directions respectively, and f is the focal length of the camera; Step 4.2: The camera attitude angle further includes a rotation angle ψ. In the camera coordinate system O c -X c Y c Z c wherein, LOS O’ is the observation vector of the camera towards the center of the earth. Construct a plane perpendicular to LOS O’ , and this plane is the LOS projection plane. Establish a polar coordinate system in the LOS projection plane, with O LOS as the pole and Ψ as the polar axis. Transform the remote sensing image and the reference map into the polar coordinate system through the projection matrix respectively. Translate the projection of the remote sensing image along the Ψ axis within the LOS projection plane, and match the translated projection of the remote sensing image with the projection of the reference map. When the two match, the angle increased by the translation of the projection of the remote sensing image along the Ψ axis is the rotation angle ψ.

2. The on-orbit geometric positioning method of a high-orbit large area array camera based on the earth's contour according to claim 1, characterized in that, Step 4.2 includes: Step 4.2.1: The projection matrix from the polar coordinates (r, Ψ) in the LOS projection plane to the image coordinate system (u, v) is calculated by the following formula: They are respectively rotation matrices for the LOS projection plane to rotate about the X c , Y c , Z c axis; Step 4.2.2: θ E is the geocentric angle corresponding to the point on the earth's surface and is calculated by the following formula: is the center O of the camera c is the distance between the point on the earth's surface and θ s = arctan(r); Step 4.2.3: The projection matrix of the LOS projection plane polar coordinates to the reference map is obtained through the following formula: (X, Y, Z) and (lon, lat, R) are the coordinates of a point on the Earth's surface in the Earth-centered inertial coordinate system and the geodetic coordinate system respectively. R is the radius of the Earth. The Xce-axis, Yce-axis, and Zce-axis are the three axes of the Earth-centered inertial coordinate system respectively. The Xce-axis lies in the equatorial plane and points to the intersection of the Greenwich meridian and the equator. The Yce-axis lies in the equatorial plane and is perpendicular to the Xce-axis. The Zce-axis is perpendicular to the equatorial plane and points to the north celestial pole. R Xce (·), R Yce (·), R Zce (·) are the rotation matrices of the LOS projection plane rotating around the Xce, Yce, and Zce axes respectively.

3. A high-orbit large area array camera on-orbit geometric positioning system based on the earth's contour, characterized in that, Includes: A model construction module that establishes an on-orbit geometric model of a high-orbit large area array camera; A contour coordinate extraction module that extracts the Earth's contour within the observation field of view of the high-orbit large area array camera according to the on-orbit geometric model of the high-orbit large area array camera established by the model construction module, establishes an image coordinate system and a focal plane coordinate system, and extracts the image coordinates of the Earth's contour points; A contour center point calculation module that calculates the center point of the Earth's contour using the image coordinates of the Earth's contour points in the contour coordinate extraction module; Attitude angle determination module, establish a camera coordinate system O c -X c Y c Z c , calculate the camera attitude angle according to the position of the center point of the earth's contour and the center of the earth in the earth contour center point calculation module; An on-orbit geometric positioning module that calculates the polar coordinates of the remote sensing image in the LOS projection plane through the azimuth and elevation angles in the camera attitude angle parameters in the attitude angle determination module; Use the rotation angle in the camera attitude angle parameters to obtain the projection of the remote sensing image when it matches the reference map projection, and perform the transformation of the image points in the remote sensing image to the geocentric fixed system coordinates of the corresponding Earth surface points to achieve on-orbit geometric positioning; In the contour coordinate extraction module, for the remote sensing image captured by the large area array camera, the Sobel operator is used to detect and extract the Earth's contour. The Sobel operator convolution kernel is: I represents the original image, G u , G v represents the image gray value after horizontal and vertical edge detection. According to the above formula (1), the image coordinates (u i , v i ) of N earth contour points are obtained; The contour center point calculation module includes calculating the position coordinates (u O’ , v O’ ) of the image point O' corresponding to the imaging of the center of the earth by the camera according to the image coordinates of N earth contour points using the least squares method. The formula is as follows: (u i , v i ) are the image coordinates of the Earth's contour points, and R is the calculated radius of the center of the circle; The attitude angle determination module includes: Step 4.1: The camera attitude angles include the azimuth angle θ and the elevation angle φ, and (θ, φ) are calculated by the following formula (3): (u O’ , v O’ ) is the position coordinate of the image point O' corresponding to the camera imaging of the center of the earth, (u0, v0) is the coordinate of the principal point of the camera in the image coordinate system, dx and dy are the pixel sizes in the x-axis and y-axis directions respectively, and f is the focal length of the camera; Step 4.2: The camera attitude angle further includes a rotation angle ψ. In the camera coordinate system O c -X c Y c Z c , LOS O’ is the observation vector of the camera towards the center of the earth. Construct a plane perpendicular to LOS O’ . This plane is the LOS projection plane. Establish a polar coordinate system in the LOS projection plane, with O LOS as the pole and Ψ as the polar axis. Transform the remote sensing image and the reference map into the polar coordinate system through the projection matrix respectively. Translate the projection of the remote sensing image along the Ψ axis within the LOS projection plane, and match the translated projection of the remote sensing image with the projection of the reference map. When the two match, the angle increased by the translation of the projection of the remote sensing image along the Ψ axis is the rotation angle ψ.

Images