Monitoring system and method for the fore-and-aft line angle and absolute pointing of a surveying camera

Abstract

This invention belongs to the field of space remote sensing and mapping technology, and particularly relates to a monitoring system and method for the included angle and absolute pointing of the fore- and rear-viewing line-of-sight of a mapping camera. The method includes: S1: using the satellite platform to side-swing and calibrate the celestial image as a reference time; S2: calculating the rotation matrices from the fore- and rear-viewing ground-based camera coordinate systems to the satellite camera coordinate system at the reference time; S3: calculating the thermal deformation matrices of the satellite camera coordinate system, the fore- and rear-viewing ground-based camera coordinate systems; S4: obtaining the real-time rotation matrices from the fore- and rear-viewing ground-based camera coordinate systems to the satellite camera coordinate system at the measurement time; S5: performing inverse cosine calculation on the two absolute pointing vectors to obtain the included angle of the fore- and rear-viewing ground-based cameras at the measurement time. This invention ensures the geometric accuracy of the mapping camera while also providing real-time measurement and comprehensive subsystem monitoring.

Description

Technical Field

[0001] This invention belongs to the field of space remote sensing and mapping technology, and particularly relates to a monitoring system and method for the included angle and absolute pointing of the front and rear viewing axes of a mapping camera. Background Technology

[0002] Three-dimensional mapping and remote sensing technology is of great significance to national defense security, agricultural production and disaster prediction. At present, while meeting the requirements of geographic resolution, the requirements for the accuracy of three-dimensional mapping are increasing, which directly translates into clear requirements for the geometric accuracy of mapping and remote sensing optical systems.

[0003] The positioning accuracy error of mapping cameras without control points mainly stems from three factors: geometric calibration error, orbit measurement error, and attitude error. Geometric calibration error and orbit measurement error can be eliminated through the application of ground control points. However, in actual satellite operation, the periodic variations in solar radiation in outer space cause periodic thermal deformation of the mapping camera structure, making the angle between the front and back sight axes unstable and exhibiting a time-varying function. Simultaneously, due to limitations in the distribution range and number of ground control points, the periodic variations in the angle between the front and back sight axes and the absolute pointing of the mapping camera cannot be completely eliminated. This problem has become a key bottleneck restricting the improvement of the geometric accuracy of mapping cameras. Therefore, it is urgent to develop a technical means to achieve real-time monitoring of the angle between the front and back sight axes and the absolute pointing under control point-less conditions.

[0004] From the perspective of existing technologies, there are two main ways to obtain the angle between the line of sight of the forward-looking and backward-looking cameras: First, based on ground calibration data, obtain the rotation matrices from the forward-looking and backward-looking cameras to the satellite system, and the rotation matrix from the satellite camera (attitude sensor) to the camera system, and derive the absolute pointing of the angle between the line of sight of the forward-looking and backward-looking cameras in the inertial frame through matrix operations; Second, through ground control point calibration, directly obtain the installation rotation matrix from the forward-looking and backward-looking cameras to the satellite camera (attitude sensor), and then obtain the absolute pointing of the angle between the line of sight of the forward-looking and backward-looking cameras in the inertial frame at the calibration time. However, in actual camera operation, low-frequency changes can cause the installation matrix between the satellite camera and the ground camera to shift, ultimately resulting in a decrease in the stability of the angle between the line of sight of the satellite and ground cameras, leading to measurement errors. Summary of the Invention

[0005] In view of this, the present invention aims to provide a monitoring system and method for the fore-and-aft viewing angle and absolute pointing of a surveying camera, in order to solve the technical problem that the geometric accuracy of a surveying camera is limited by the viewing angle under uncontrolled conditions. The present invention is based on a beam splitter to construct a multi-beam monitoring system to measure the viewing angle of the subsystem, thereby realizing on-orbit monitoring of the fore-and-aft viewing angle and absolute pointing of the surveying camera. The present invention ensures the geometric accuracy of the surveying camera while also possessing the real-time measurement capability and the comprehensiveness of the subsystem monitoring.

[0006] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0007] A monitoring system for the forward and backward viewing angles and absolute pointing of a mapping camera includes: a collimating and expanding light source, a beam-splitting reference prism, a first beam-splitting module, a first reflector, a star camera, a second beam-splitting module, a third beam-splitting module, a fourth beam-splitting module, a second reflector, a forward-looking ground camera, a third reflector, and a backward-looking ground camera. The light emitted from the collimating and expanding light source is split into a first beam and a second beam by the beam-splitting reference prism. The first beam is split into a third beam and a fourth beam by the first beam-splitting module. The third beam and the fourth beam are reflected by the first reflector. Then, the light enters the star camera for imaging, obtaining the first and second light spots; the second beam is split into the fifth and sixth beams by the second beam splitting module, the fifth beam is split into the seventh and eighth beams by the third beam splitting module, the seventh and eighth beams are reflected by the second reflector and enter the forward-looking ground camera for imaging, obtaining the third and fourth light spots; the sixth beam is split into the ninth and tenth beams by the fourth beam splitting module, the ninth and tenth beams are reflected by the third reflector and enter the rear-looking ground camera for imaging, obtaining the fifth and sixth light spots.

[0008] Furthermore, the first, second, third, and fourth beam splitting modules can all employ Dammann gratings, dichroic mirrors, or semi-reflective lenses.

[0009] A method for monitoring the fore-and-aft line-of-sight angle and absolute pointing of a surveying camera, implemented using a monitoring system for the fore-and-aft line-of-sight angle and absolute pointing of the surveying camera, specifically includes the following steps:

[0010] S1: By tilting the satellite platform, the star camera, forward-looking ground camera, and backward-looking ground camera simultaneously image the sky, and the time of sky imaging calibration is used as the reference time. Obtain the attitude matrix of the star camera coordinate system, the forward-looking ground camera measurement coordinate system, and the backward-looking ground camera measurement coordinate system in the inertial coordinate system J2000; the unit vector of the line of sight of the forward-looking ground camera in the forward-looking ground camera measurement coordinate system; the unit vector of the line of sight of the backward-looking ground camera in the backward-looking ground camera measurement coordinate system; the coordinate values ​​of the centroids of the first and second light spots in the star camera CMOS coordinate system; the coordinate values ​​of the centroids of the third and fourth light spots in the forward-looking ground camera CMOS coordinate system; and the coordinate values ​​of the centroids of the fifth and sixth light spots in the backward-looking ground camera CMOS coordinate system.

[0011] S2: Based on step S1, calculate the rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time and the rotation matrix from the rear-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time.

[0012] S3: Define the working time of the monitoring system after the reference time as the measurement time; Based on the centroid coordinates of each spot at the reference time and the measurement time, and combined with the optical parameters of the star camera, the forward-looking ground camera and the backward-looking ground camera, calculate the thermal deformation matrix of the star camera coordinate system, the forward-looking ground camera measurement coordinate system and the backward-looking ground camera measurement coordinate system at the measurement time.

[0013] S4: Based on the thermal deformation matrices of the star camera coordinate system, the forward-looking ground camera measurement coordinate system, and the backward-looking ground camera measurement coordinate system at the measurement time, obtain the real-time rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system and the real-time rotation matrix from the backward-looking ground camera measurement coordinate system to the star camera coordinate system.

[0014] S5: Based on the QUEST algorithm, calculate the rotation matrix from the star camera coordinate system to the inertial coordinate system J2000. Combine the real-time rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system and the real-time rotation matrix from the rear-looking ground camera measurement coordinate system to the star camera coordinate system to obtain the absolute pointing vector of the forward-looking ground camera's line of sight in the inertial coordinate system J2000, and the absolute pointing vector of the rear-looking ground camera's line of sight in the inertial coordinate system J2000. Then, perform inverse cosine calculation on the two absolute pointing vectors to obtain the angle between the line of sight of the forward-looking ground camera and the line of sight of the rear-looking ground camera at the measurement time.

[0015] Furthermore, the star camera coordinate system is a three-dimensional coordinate system established with the projection center of the star camera as the origin. The Z-axis of the star camera coordinate system coincides with the optical axis of the star camera. The X-axis of the star camera coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the star camera. The Y-axis of the star camera coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the star camera.

[0016] The forward-looking camera measurement coordinate system is a three-dimensional coordinate system established with the projection center of the forward-looking camera as the origin. The Z-axis of the forward-looking camera measurement coordinate system coincides with the optical axis of the forward-looking camera. The X-axis of the forward-looking camera measurement coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the forward-looking camera. The Y-axis of the forward-looking camera measurement coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the forward-looking camera.

[0017] The rear-view camera measurement coordinate system is a three-dimensional coordinate system established with the projection center of the rear-view camera as the origin. The Z-axis of the rear-view camera measurement coordinate system coincides with the optical axis of the rear-view camera. The X-axis of the rear-view camera measurement coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the rear-view camera. The Y-axis of the rear-view camera measurement coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the rear-view camera.

[0018] The CMOS coordinate system of the star camera is a two-dimensional coordinate system established with the center of the focal plane of the star camera as the origin. The X-axis of the CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the star camera, and the Y-axis of the CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the star camera.

[0019] The forward-looking ground-view camera CMOS coordinate system is a two-dimensional coordinate system established with the center of the focal plane of the forward-looking ground-view camera as the origin. The X-axis of the forward-looking ground-view camera CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the forward-looking ground-view camera, and the Y-axis of the forward-looking ground-view camera CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the forward-looking ground-view camera.

[0020] The rear-view camera CMOS coordinate system is a two-dimensional coordinate system established with the center of the focal plane of the rear-view camera as the origin. The X-axis of the rear-view camera CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the rear-view camera, and the Y-axis of the rear-view camera CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the rear-view camera.

[0021] Furthermore, in step S2, the rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time and the rotation matrix from the backward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time are calculated using the following formulas:

[0022] ;

[0023] in, The rotation matrix from the forward-looking ground camera coordinate system to the star camera coordinate system at the reference time. The rotation matrix from the back-view ground camera coordinate system to the star camera coordinate system at the reference time. The attitude matrix of the star camera coordinate system in the inertial coordinate system J2000 is given. To measure the attitude matrix of the forward-looking ground camera coordinate system in the inertial coordinate system J2000, The attitude matrix of the rear-view ground camera's coordinate system in the inertial coordinate system J2000 is measured.

[0024] Furthermore, in step S3, based on the coordinate values ​​of the centroids of the first and second light spots in the star camera CMOS coordinate system and the optical parameters of the star camera, the thermal deformation rotation matrix of the star camera coordinate system at the measurement time is calculated using the thermal deformation rotation matrix calculation method.

[0025] Based on the coordinates of the centroids of the third and fourth light spots in the CMOS coordinate system of the forward-looking camera and the optical parameters of the forward-looking camera, the thermal deformation rotation matrix of the forward-looking camera measurement coordinate system at the measurement time is calculated using the thermal deformation rotation matrix calculation method.

[0026] Based on the coordinates of the centroids of the fifth and sixth light spots in the CMOS coordinate system of the rear-view camera and the optical parameters of the rear-view camera, the thermal deformation rotation matrix of the rear-view camera measurement coordinate system at the measurement time is calculated using the thermal deformation rotation matrix calculation method.

[0027] Furthermore, based on the coordinates of the centroids of the first and second light spots in the star camera's CMOS coordinate system and the optical parameters of the star camera, the specific steps for calculating the thermal deformation rotation matrix of the star camera coordinate system at the measurement time using the thermal deformation rotation matrix calculation method are as follows:

[0028] The focal length of the star camera is Fs, and the pixel length on the focal plane of the star camera is μ. S Then the coordinates of the origin of the star camera's CMOS coordinate system in the star camera coordinate system are (X... CS ,Y CS ,-F S );

[0029] At the reference time, the coordinates of the centroid of the first light spot in the star camera CMOS coordinate system are (X... as0 ,Y as0 The centroid of the second light spot in the star camera CMOS coordinate system has the coordinates (X... bs0 ,Y bs0 );

[0030] At the reference time, based on the optical parameters of the star camera and the centroid coordinates of the first and second light spots in the star camera's CMOS coordinate system, the spatial vector of the third beam at the reference time under the star camera is calculated. and the reference time space vector of the fourth beam under the star camera :

[0031] ;

[0032] ;

[0033] in, Let X be the x-coordinate of the origin of the star camera CMOS coordinate system in the star camera coordinate system. The Y-coordinate of the origin of the CMOS coordinate system of the star camera in the star camera coordinate system;

[0034] At the measurement moment, the deformation of the star camera causes displacement of the positions of the first and second light spots. Therefore, the coordinates of the centroid of the first light spot in the CMOS coordinate system are (X... as1 ,Y as1 The centroid of the second spot in the CMOS coordinate system is (X... bs1 ,Y bs1 );

[0035] At the measurement moment, based on the optical parameters of the star camera and the centroid coordinates of the first and second light spots in the star camera's CMOS coordinate system, the spatial vector of the third beam at the measurement moment under the star camera is calculated accordingly. and the space vector of the measurement time under the star camera of the fourth beam :

[0036] ;

[0037] ;

[0038] in, Let X be the X-coordinate of the origin of the CMOS coordinate system of the star camera in the star camera coordinate system. The Y-coordinate of the origin of the CMOS coordinate system of the star camera in the star camera coordinate system;

[0039] The first rotation matrix M0S corresponding to the reference time space vector and the second rotation matrix M1S corresponding to the measurement time space vector in the star camera coordinate system are calculated using the following formulas:

[0040] ;

[0041] ;

[0042] Based on the first rotation matrix M 0S Second rotation matrix M 1S Calculate the thermal deformation rotation matrix R of the star camera coordinate system at the measurement time. S :

[0043] .

[0044] Furthermore, in step S4, combining the thermal deformation matrices of the star camera coordinate system, the forward-looking ground camera measurement coordinate system, and the backward-looking ground camera measurement coordinate system at the measurement time, the real-time rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system is calculated using the following formula. And the real-time rotation matrix from the rear-view ground camera measurement coordinate system to the star camera coordinate system. :

[0045] ;

[0046] in, Let be the transpose of the thermal deformation matrix in the star camera coordinate system. The rotation matrix from the forward-looking ground camera coordinate system to the star camera coordinate system at the reference time. The rotation matrix from the back-view ground camera coordinate system to the star camera coordinate system at the reference time. The thermal deformation matrix of the coordinate system for the forward-looking ground camera measurement. The thermal deformation matrix of the measurement coordinate system for the rear-view ground camera.

[0047] Furthermore, in step S5, the rotation matrix from the star camera coordinate system to the inertial coordinate system is obtained based on the QUEST algorithm. The absolute pointing vector of the forward-looking camera's line of sight in the inertial coordinate system J2000 is calculated using the following formula. And the absolute pointing vector of the rear-view camera's line of sight in the inertial coordinate system J2000. :

[0048] ;

[0049] in, The real-time rotation matrix from the forward-looking ground camera coordinate system to the star camera coordinate system. The real-time rotation matrix from the rear-view ground camera coordinate system to the star camera coordinate system. Let be the unit vector of the line of sight of the forward-looking camera in the forward-looking camera measurement coordinate system. Let be the unit vector of the line of sight of the rear-view camera in the rear-view camera measurement coordinate system.

[0050] Furthermore, in step S5, the absolute pointing vector of the forward-looking camera's line of sight in the inertial coordinate system J2000 is used. The absolute pointing vector of the rear-view camera's line of sight in the inertial coordinate system J2000. The angle between the line of sight of the forward-looking camera and the line of sight of the rear-looking camera is calculated using the following formula. :

[0051] .

[0052] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0053] (1) The monitoring system and method for the front and rear view angles and absolute pointing of the surveying camera created by the present invention can perform uncontrolled monitoring of the front and rear view angles and absolute pointing of the dual-head front and rear view surveying camera, thereby improving the geometric positioning accuracy of the surveying camera.

[0054] (2) The monitoring system and method for the front and rear viewing angles and absolute pointing of the surveying camera created by the present invention has a simple structure and high thermal stability.

[0055] (3) The monitoring system and method for the front and rear viewing angles and absolute pointing of the surveying camera created by the present invention can achieve uncontrolled monitoring of the drift of the viewing axis of multiple subsystems on the load and has a high degree of information redundancy.

[0056] (4) The present invention creates a monitoring system and method for the front and rear viewing angles and absolute orientation of the surveying camera, which uses a Damman grating for beam splitting, improves the imaging quality of the monitoring beam, and improves the centroid calculation accuracy, thereby achieving precise monitoring of the viewing axis. Attached Figure Description

[0057] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0058] Figure 1 A schematic diagram of the structure of the monitoring system for the front and rear viewing angles and absolute pointing of the mapping camera described in the embodiment of the present invention;

[0059] Figure 2 A flowchart illustrating the method for monitoring the fore-and-aft viewing angle and absolute pointing of a mapping camera according to an embodiment of the present invention;

[0060] Figure 3 A schematic diagram of the structure of the monitoring method for the front and rear viewing angles and absolute pointing of the mapping camera described in the embodiment of the present invention;

[0061] Figure 4 This is a schematic diagram illustrating the structure of the rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time and the rotation matrix from the rear-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time, as described in the embodiment of the present invention.

[0062] Explanation of reference numerals in the attached figures:

[0063] 1. Collimated beam expander; 2. Beam splitting reference prism; 3. First beam splitting module; 4. First reflector; 5. Star camera; 6. Second beam splitting module; 7. Third beam splitting module; 8. Second reflector; 9. Forward-looking ground camera; 10. Fourth beam splitting module; 11. Third reflector; 12. Rear-looking ground camera. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0065] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0066] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0067] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0068] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0069] The current calibration method of "ground camera to ground, satellite camera to 5-star" can accurately obtain the angle between the front and rear sight axes and the absolute pointing at the time of calibration, but it has significant limitations: Under satellite conditions, thermal deformation exhibits time-varying characteristics, and ground control points cannot capture the dynamic changes in the angle between the front and rear sight axes in real time, which makes it difficult to effectively correct the mapping data errors in some key areas, seriously restricting the improvement of the geometric accuracy of the mapping camera.

[0070] Further analysis reveals three key problems with the method of obtaining the angle between the front and back sight axes of the mapping camera based on ground control point calibration: First, the positioning accuracy is significantly poor in areas without ground control points; second, data acquisition relies on ground control points, resulting in low timeliness; and third, the ability to analyze the subsystems of the satellite payload is insufficient, making it impossible to conduct specialized thermal analysis and error correction for individual optical systems, thus making it difficult to ensure mapping accuracy at the subsystem level.

[0071] To address the aforementioned technical challenges, this invention proposes an innovative solution: a multi-beam monitoring system based on a beam splitter prism. This system enables precise measurement of the line-of-sight pointing of the subsystem, ultimately achieving real-time on-orbit monitoring of the angle between the front and rear line-of-sight axes and the absolute pointing of the mapping camera. This invention not only effectively guarantees the geometric accuracy of the mapping camera but also possesses two core advantages: firstly, it achieves real-time measurement, solving the problem of poor timeliness in traditional methods; secondly, it covers the comprehensiveness of subsystem monitoring, filling the technical gap where a single optical system cannot be specifically subjected to thermal analysis and correction.

[0072] like Figure 1 The present invention proposes a monitoring system for the front-to-back viewing angle and absolute pointing of a mapping camera, comprising: a collimating beam expander 1, a beam splitting reference prism 2, a first beam splitting module 3, a first reflector 4, a star camera 5, a second beam splitting module 6, a third beam splitting module 7, a fourth beam splitting module 10, a second reflector 8, a forward-looking ground camera 9, a third reflector 11, and a rear-looking ground camera 12. The light emitted from the collimating beam expander 1 is split into a first beam and a second beam by the beam splitting reference prism 2. The first beam is split into a third beam and a fourth beam by the first beam splitting module 3. The third beam and the fourth beam are then... After being reflected by the first reflector 4, the light enters the star camera 5 for imaging, obtaining the first and second light spots. The second beam of light is split into the fifth and sixth beams by the second beam splitting module 6. The fifth beam of light is split into the seventh and eighth beams by the third beam splitting module 7. The seventh and eighth beams of light are reflected by the second reflector 8 and enter the forward-looking ground camera 9 for imaging, obtaining the third and fourth light spots. The sixth beam of light is split into the ninth and tenth beams by the fourth beam splitting module 10. The ninth and tenth beams of light are reflected by the third reflector 11 and enter the rear-looking ground camera 12 for imaging, obtaining the fifth and sixth light spots.

[0073] It should be noted that the collimating and beam-expanding light source 1 refers to a laser light source assembly with dual functions of "collimation" and "beam expansion". The first reflector 4, the second reflector 8, and the third reflector 11 are used to fold the optical path, thereby miniaturizing the system. This invention aims to solve the technical problem that the geometric accuracy of a surveying camera is limited by the line-of-sight pointing under uncontrolled conditions, and provides a monitoring system for the angle and absolute pointing of the forward and rearward lines of sight of a surveying camera under uncontrolled on-orbit conditions. The on-orbit monitoring system for the angle and absolute pointing of the forward and rearward lines of sight of a surveying camera includes: a high-stability laser light source, a beam splitter prism (i.e., beam splitting reference prism 2), a Damman grating, a star camera 5 (attitude sensor), a forward-looking ground camera 9, and a rearward-looking ground camera 12.

[0074] Its monitoring optical path is divided into three parts, which monitor the star camera 5 (attitude sensor), the forward-looking ground camera 9, and the rear-looking ground camera 12 respectively. By combining the monitoring results of the three beams, the angle between the forward and rear-looking axes and the absolute direction of the mapping camera are obtained.

[0075] Star Camera 5 (Attitude Sensor) Monitoring Link: After the laser source is collimated and expanded, it is split into two collimated parallel beams after passing through the beam splitting reference prism 2. The transmitted light is incident on the first beam splitting module 3, which splits the incident parallel beams into two parallel beams. The angle between the two beams is related to the period of the Dammann grating structure. Where d is the grating period, It is the wavelength of the light source, It is the beam splitting angle, and m is the diffraction order.

[0076] After passing through the first reflecting mirror 4, the light enters the star camera 5 and is reflected in the focal plane of the star camera 5 as a pair of monitoring images (specifically, the first light spot and the second light spot).

[0077] The forward-looking ground camera 9 monitoring link: After the laser light source is collimated and expanded, it is split into two collimated parallel beams after passing through the beam splitting reference prism 2. The reflected light is incident on the second beam splitting module 6, which splits the incident parallel beams into two parallel beams. One of the parallel beams is incident on the third beam splitting module 7, and after passing through the second reflecting mirror 8, it is incident on the forward-looking ground camera 9. It is manifested as a pair of monitoring spots (specifically the third spot and the fourth spot) on the focal plane of the forward-looking ground camera 9.

[0078] The monitoring link of the rear-view camera 12: After the laser light source is collimated and expanded, it is split into two collimated parallel beams after passing through the beam splitting reference prism 2. The reflected light is incident on the second beam splitting module 6, and the incident parallel beam is split into two parallel beams. One of the parallel beams is incident on the fourth beam splitting module 10, and after passing through the third reflector 11, it is incident on the rear-view camera 12. It is manifested as a pair of monitoring image spots (specifically the fifth and sixth light spots) on the focal plane of the rear-view camera 12.

[0079] In some embodiments, the first beam splitting module 3, the second beam splitting module 6, the third beam splitting module 7, and the fourth beam splitting module 10 can all be made of Dammann grating, dichroic mirror, or semi-reflective semi-transparent mirror.

[0080] like Figure 2 As shown, this invention proposes a method for monitoring the fore-and-aft line-of-sight angle and absolute pointing of a surveying camera. This method utilizes a monitoring system for the fore-and-aft line-of-sight angle and absolute pointing of the surveying camera, and specifically includes the following steps:

[0081] S1: By tilting the satellite platform, simultaneously image the sky using the star camera 5, the forward-looking ground camera 9, and the rear-looking ground camera 12, and use the time of sky imaging calibration as the reference time. Obtain the attitude matrices of the star camera coordinate system, the forward-looking ground camera measurement coordinate system, and the rear-looking ground camera measurement coordinate system in the inertial coordinate system J2000; the unit vector of the line of sight of the forward-looking ground camera 9 in the forward-looking ground camera measurement coordinate system; the unit vector of the line of sight of the rear-looking ground camera 12 in the rear-looking ground camera measurement coordinate system; the coordinate values ​​of the centroids of the first and second light spots in the star camera CMOS coordinate system; the coordinate values ​​of the centroids of the third and fourth light spots in the forward-looking ground camera CMOS coordinate system; and the coordinate values ​​of the centroids of the fifth and sixth light spots in the rear-looking ground camera CMOS coordinate system.

[0082] S2: Based on step S1, calculate the rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time and the rotation matrix from the rear-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time.

[0083] S3: Define the working time of the monitoring system after the reference time as the measurement time; Based on the centroid coordinates of each spot at the reference time and the measurement time, and combined with the optical parameters of the star camera 5, the forward-looking ground camera 9 and the backward-looking ground camera 12, calculate the thermal deformation matrix of the star camera coordinate system, the forward-looking ground camera measurement coordinate system and the backward-looking ground camera measurement coordinate system at the measurement time.

[0084] S4: Based on the thermal deformation matrices of the star camera coordinate system, the forward-looking ground camera measurement coordinate system, and the backward-looking ground camera measurement coordinate system at the measurement time, obtain the real-time rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system and the real-time rotation matrix from the backward-looking ground camera measurement coordinate system to the star camera coordinate system.

[0085] S5: Based on the QUEST algorithm, calculate the rotation matrix from the star camera coordinate system to the inertial coordinate system J2000. Combine the real-time rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system and the real-time rotation matrix from the rear-looking ground camera measurement coordinate system to the star camera coordinate system to obtain the absolute pointing vector of the line of sight of the forward-looking ground camera 9 in the inertial coordinate system J2000 and the absolute pointing vector of the line of sight of the rear-looking ground camera 12 in the inertial coordinate system J2000. Then, perform inverse cosine calculation on the two absolute pointing vectors to obtain the angle between the line of sight of the forward-looking ground camera 9 and the line of sight of the rear-looking ground camera 12 at the measurement time.

[0086] It should be noted that this invention addresses the thermal drift problem of the fore- and rear-view axes of dual-head mapping cameras under on-orbit conditions. It utilizes a highly stable reference prism to monitor the subsystem's line of sight and combines calibration data to measure the angle between the fore- and rear-view axes of the dual-head mapping cameras. Overall, it achieves the following functions: 1. On-orbit monitoring of the dual-head mapping cameras' line of sight, achieving precise measurement of the angle and absolute pointing of the fore- and rear-view camera's lines of sight, while also monitoring and measuring the thermal drift of the subsystem's line of sight; 2. A structured optical path is proposed that simultaneously associates the fore- and rear-view cameras with the satellite camera 5 (attitude sensor), resulting in a simple, compact, and highly stable structure; 3. The use of a Dammann grating for beam splitting improves the quality of the light spot, thereby enhancing the accuracy of centroid extraction and enabling precise measurement of the line of sight pointing.

[0087] Furthermore, in step S1, the time when the satellite platform tilts to image the sky is defined as the reference time. Using the satellite platform tilting method, the star camera 5 (attitude sensor), the forward-looking ground camera 9, and the rear-looking ground camera 12 simultaneously image the sky, obtaining the attitude matrix of the star camera coordinate system in the inertial coordinate system. The attitude matrix of the forward-looking camera measurement coordinate system in the inertial coordinate system. And the attitude matrix of the rear-view camera measurement coordinate system in the inertial coordinate system. The unit vectors of the line-of-sight axes of the forward-looking ground camera 9 and the backward-looking ground camera 12 in the forward and backward-looking measurement coordinate systems are: , .

[0088] In some embodiments, the star camera coordinate system is a three-dimensional coordinate system established with the projection center of the star camera 5 as the origin. The Z-axis of the star camera coordinate system coincides with the optical axis of the star camera 5. The X-axis of the star camera coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the star camera 5. The Y-axis of the star camera coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the star camera 5.

[0089] The forward-looking ground camera measurement coordinate system is a three-dimensional coordinate system established with the projection center of the forward-looking ground camera 9 as the origin. The Z-axis of the forward-looking ground camera measurement coordinate system coincides with the optical axis of the forward-looking ground camera 9. The X-axis of the forward-looking ground camera measurement coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the forward-looking ground camera 9. The Y-axis of the forward-looking ground camera measurement coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the forward-looking ground camera 9.

[0090] The rear-view camera measurement coordinate system is a three-dimensional coordinate system established with the projection center of the rear-view camera 12 as the origin. The Z-axis of the rear-view camera measurement coordinate system coincides with the optical axis of the rear-view camera 12. The X-axis of the rear-view camera measurement coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the rear-view camera 12. The Y-axis of the rear-view camera measurement coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the rear-view camera 12.

[0091] The star camera CMOS coordinate system is a two-dimensional coordinate system established with the center of the focal plane of star camera 5 as the origin. The X-axis of the star camera CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of star camera 5, and the Y-axis of the star camera CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of star camera 5.

[0092] The forward-viewing ground camera CMOS coordinate system is a two-dimensional coordinate system established with the center of the focal plane of the forward-viewing ground camera 9 as the origin. The X-axis of the forward-viewing ground camera CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the forward-viewing ground camera 9, and the Y-axis of the forward-viewing ground camera CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the forward-viewing ground camera 9.

[0093] The rear-view camera CMOS coordinate system is a two-dimensional coordinate system established with the center of the focal plane of the rear-view camera 12 as the origin. The X-axis of the rear-view camera CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the rear-view camera 12, and the Y-axis of the rear-view camera CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the rear-view camera 12.

[0094] In some embodiments, in step S2, the rotation matrix from the forward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time and the rotation matrix from the backward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time are calculated using the following formulas:

[0095] ;

[0096] in, The rotation matrix from the forward-looking ground camera coordinate system to the star camera coordinate system at the reference time. The rotation matrix from the back-view ground camera coordinate system to the star camera coordinate system at the reference time. The attitude matrix of the star camera coordinate system in the inertial coordinate system J2000 is given. To measure the attitude matrix of the forward-looking ground camera coordinate system in the inertial coordinate system J2000, The attitude matrix of the rear-view ground camera's coordinate system in the inertial coordinate system J2000 is measured.

[0097] It should be noted that the working time after the monitoring system calibrates the sky imaging is the measurement time. Based on the TRIAD algorithm, the thermal deformation rotation matrix R of the star camera 5 (attitude sensor) coordinate system, the forward-looking ground camera measurement coordinate system, and the backward-looking ground camera 12 coordinate measurement coordinate system at the measurement time is obtained by combining the spot position. S R C1 and R C2 .

[0098] In some embodiments, in step S3, based on the coordinate values ​​of the centroids of the first and second light spots in the star camera CMOS coordinate system and the optical parameters of the star camera 5, the thermal deformation rotation matrix R of the star camera coordinate system at the measurement time is calculated using the thermal deformation rotation matrix calculation method. S ;

[0099] Based on the coordinates of the centroids of the third and fourth light spots in the CMOS coordinate system of the forward-looking camera and the optical parameters of the forward-looking camera 9, the thermal deformation rotation matrix R of the forward-looking camera measurement coordinate system at the measurement time is calculated using the thermal deformation rotation matrix calculation method. C1 ;

[0100] Based on the coordinates of the centroids of the fifth and sixth light spots in the CMOS coordinate system of the rear-view camera and the optical parameters of the rear-view camera 12, the thermal deformation rotation matrix R of the rear-view camera measurement coordinate system at the measurement time is calculated using the thermal deformation rotation matrix calculation method. C2 .

[0101] In some embodiments, based on the coordinates of the centroids of the first and second light spots in the star camera CMOS coordinate system and the optical parameters of the star camera 5, the specific steps for calculating the thermal deformation rotation matrix of the star camera coordinate system at the measurement time using the thermal deformation rotation matrix calculation method are as follows:

[0102] The focal length of Star Camera 5 is Fs, and the pixel length on the focal plane of Star Camera 5 is μ. S Then the coordinates of the origin of the star camera CMOS coordinate system in the star camera coordinate system are (X... CS ,Y CS ,-F S );

[0103] At the reference time, the coordinates of the centroid of the first light spot in the star camera CMOS coordinate system are (X...as0 ,Y as0 The centroid of the second light spot in the star camera CMOS coordinate system has the coordinates (X... bs0 ,Y bs0 );

[0104] At the reference time, based on the optical parameters of Star Camera 5 and the centroid coordinates of the first and second light spots in the Star Camera CMOS coordinate system, the spatial vector of the third beam at the reference time under Star Camera 5 is calculated. and the reference time space vector of the fourth beam under Star Camera 5 :

[0105] ;

[0106] ;

[0107] in, The coordinate of the origin of the star camera CMOS coordinate system in the X direction within the star camera coordinate system is given. The coordinate of the origin of the CMOS coordinate system of the star camera in the Y direction under the star camera coordinate system;

[0108] At the measurement moment, the deformation of the star camera 5 causes displacement of the positions of the first and second light spots. Therefore, the coordinates of the centroid of the first light spot in the CMOS coordinate system are (X... as1 ,Y as1 The centroid of the second spot in the CMOS coordinate system is (X... bs1 ,Y bs1 );

[0109] At the measurement moment, based on the optical parameters of star camera 5 and the centroid coordinates of the first and second light spots in the star camera CMOS coordinate system, the spatial vector of the third beam at the measurement moment under star camera 5 is calculated accordingly. and the space vector of the measurement time of the fourth beam under Star Camera 5 :

[0110] ;

[0111] ;

[0112] in, Let X be the x-coordinate of the origin of the star camera CMOS coordinate system in the star camera coordinate system. The Y-coordinate of the origin of the CMOS coordinate system of the star camera in the star camera coordinate system;

[0113] The first rotation matrix M0S corresponding to the reference time space vector and the second rotation matrix M1S corresponding to the measurement time space vector in the star camera coordinate system are calculated using the following formulas:

[0114] ;

[0115] ;

[0116] Based on the first rotation matrix M 0S Second rotation matrix M 1S Calculate the thermal deformation rotation matrix R of the star camera coordinate system at the measurement time. S :

[0117] ;

[0118] Similarly, based on the coordinates of the centroids of the third and fourth light spots in the CMOS coordinate system of the forward-looking camera and the optical parameters of the forward-looking camera 9, the specific steps for calculating the thermal deformation rotation matrix of the forward-looking camera measurement coordinate system at the measurement time using the thermal deformation rotation matrix calculation method are as follows:

[0119] The focal length of the forward-looking ground camera 9 is F. C1 The pixel length on the focal plane of the forward-looking camera 9 is μ. C1 The coordinates of the origin of the forward-looking camera's CMOS coordinate system in the forward-looking camera's measurement coordinate system are (X... CC1 ,Y CC1 ,-F C1 );

[0120] At the reference time, the coordinates of the centroid of the third light spot in the forward-looking camera CMOS coordinate system are (X... aC10 ,Y aC10 The centroid of the fourth light spot in the forward-looking camera CMOS coordinate system has the following coordinates: (X...) bC10 ,Y bC10 );

[0121] At the reference time, based on the optical parameters of the forward-looking camera 9, the centroid coordinates of the third spot and the fourth spot in the forward-looking camera CMOS coordinate system, the reference time space vector of the seventh beam in the forward-looking camera measurement coordinate system is calculated. and the reference time space vector of the eighth beam in the forward-looking camera measurement coordinate system :

[0122] ;

[0123] ;

[0124] in, The X-coordinate of the origin of the forward-looking camera's CMOS coordinate system in the forward-looking camera's measurement coordinate system. The Y-coordinate of the origin of the forward-looking camera's CMOS coordinate system in the forward-looking camera's measurement coordinate system;

[0125] At the measurement moment, the deformation of the forward-looking ground camera 9 causes a displacement in the positions of the third and fourth light spots. The coordinates of the centroid of the third light spot in the CMOS coordinate system are (X... aC11 ,Y aC11 The centroid of the fourth spot in the CMOS coordinate system is (X... bC11 ,Y bC11 );

[0126] At the measurement moment, based on the optical parameters of the forward-looking camera 9, the centroid coordinates of the third and fourth light spots in the forward-looking camera CMOS coordinate system, the spatial vector of the seventh beam in the forward-looking camera measurement coordinate system at the measurement moment is calculated accordingly. and the measurement vector of the eighth beam in the forward-looking camera measurement coordinate system :

[0127] ;

[0128] ;

[0129] in, The X-coordinate of the origin of the forward-looking camera's CMOS coordinate system in the forward-looking camera's measurement coordinate system. The Y-coordinate of the origin of the forward-looking camera's CMOS coordinate system in the forward-looking camera's measurement coordinate system;

[0130] The first rotation matrix M corresponding to the reference time space vector in the forward-looking camera measurement coordinate system is calculated using the following formula. 0C1 The second rotation matrix M corresponding to the space vector at the measurement time. 1C1 :

[0131] ;

[0132] ;

[0133] Based on the first rotation matrix M 0C1 Second rotation matrix M 1C1 Calculate the thermal deformation rotation matrix R of the forward-looking camera measurement coordinate system at the measurement time. C1 :

[0134] .

[0135] Based on the coordinates of the centroids of the fifth and sixth light spots in the CMOS coordinate system of the rear-view camera and the optical parameters of the rear-view camera 12, the specific steps for calculating the thermal deformation rotation matrix of the rear-view camera measurement coordinate system at the measurement time using the thermal deformation rotation matrix calculation method are as follows:

[0136] The focal length of the rear-view ground camera 12 is F. C2 The pixel length on the focal plane of the rear-view camera 12 is μ. C2 Then the coordinates of the origin of the rear-view camera CMOS coordinate system in the rear-view camera measurement coordinate system are (X... CC2 ,Y CC2 ,-F C2 );

[0137] At the reference time, the coordinates of the centroid of the fifth light spot in the rear-view camera CMOS coordinate system are (X... aC20 ,Y aC20 The centroid of the sixth light spot in the rear-view camera CMOS coordinate system has the following coordinates: (X...) bC20 ,Y bC20 );

[0138] At the reference time, based on the optical parameters of the rear-view camera 12, the centroid coordinates of the fifth and sixth light spots in the rear-view camera CMOS coordinate system, the spatial vector of the ninth beam at the reference time in the rear-view camera measurement coordinate system is calculated. and the reference time space vector of the tenth beam in the rear-view camera measurement coordinate system :

[0139] ;

[0140] ;

[0141] in, Let X be the coordinate of the origin of the rear-view camera's CMOS coordinate system in the rear-view camera's measurement coordinate system. The Y-coordinate of the origin of the rear-view camera's CMOS coordinate system in the rear-view camera's measurement coordinate system;

[0142] At the measurement moment, the deformation of the rear-view camera 12 causes a displacement in the positions of the fifth and sixth light spots. The coordinates of the centroid of the fifth light spot in the CMOS coordinate system are (X... aC21 ,Y aC21 The centroid of the sixth spot in the CMOS coordinate system is (X... bC21 ,Y bC21 );

[0143] At the measurement moment, based on the optical parameters of the rear-view camera 12, the centroid coordinates of the fifth and sixth light spots in the CMOS coordinate system, the spatial vector of the ninth beam in the rear-view camera measurement coordinate system at the measurement moment is calculated accordingly. The measurement vector of the tenth beam in the rear-view camera measurement coordinate system :

[0144] ;

[0145] ;

[0146] in, Let X be the coordinate of the origin of the rear-view camera's CMOS coordinate system in the rear-view camera's measurement coordinate system. The Y-coordinate of the origin of the rear-view camera's CMOS coordinate system in the rear-view camera's measurement coordinate system;

[0147] The first rotation matrix M corresponding to the reference time space vector in the back-view camera measurement coordinate system is calculated using the following formula. 0C2 The second rotation matrix M corresponding to the space vector at the measurement time. 1C2 :

[0148] ;

[0149] ;

[0150] Based on the first rotation matrix M 0C2 Second rotation matrix M 1C2 Calculate the thermal deformation rotation matrix R of the back-view ground camera measurement coordinate system. C2 :

[0151] .

[0152] The calculation methods for the thermal deformation matrices of the star camera coordinate system, the forward-looking ground camera measurement coordinate system, and the backward-looking ground camera measurement coordinate system are described in detail below:

[0153] (1) Thermal deformation rotation matrix R of the star camera coordinate system S :

[0154] Parallel light beams (the third and fourth beams) at a certain angle pass through star camera 5, forming a pair of light spots (the first and second light spots) at the focal plane. The monitoring vector of the star camera coordinate system is constructed using the third and fourth beams, where the monitoring vector of the third beam at the reference time is v. as0 The third beam monitoring vector at the measurement time is represented as v. as1 The fourth beam monitoring vector at the reference time is v. bs0The fourth beam monitoring vector at the measurement time is represented as v. bs1 Let the pixel size be μ. S If the focal length of the optical system is Fs, then the coordinates of the origin of the star camera's CMOS coordinate system in the star camera coordinate system are (X... CS ,Y CS ,-F S At the reference time, the centroid coordinates of the first and second light spots in the star camera CMOS coordinate system are (X... as0 ,Y as0 ), (X bs0 ,Y bs0 Then, the reference time space vector of the third beam under the initial standard state in star camera 5 can be calculated. and the reference time space vector of the fourth beam under Star Camera 5 :

[0155] ;

[0156] ;

[0157] Changes in environmental conditions cause deformation of the optical system under test, resulting in a change in the centroid of the measurement spot. Therefore, the coordinates of the two spots at the measurement moment in the star camera's CMOS coordinate system are (X...). as1 ,Y as1 ), (X bs1 ,Y bs1 The space vector of the third beam measured by Star Camera 5 and the space vector of the measurement time of the fourth beam under Star Camera 5 Represented as:

[0158] ;

[0159] ;

[0160] By using the normalized cross product and calculating the projection of the three-axis vectors corresponding to the measured time and reference time into the star camera coordinate system, the first rotation matrix M corresponding to the reference time spatial vector in the star camera coordinate system is constructed. 0S The second rotation matrix M corresponding to the space vector at the measurement time. 1S :

[0161] ;

[0162] ;

[0163] The rotation matrix between the dual-vector measurement time and the standard initial state, i.e., the thermal deformation rotation matrix R of the star camera coordinate system at the measurement time, is... Sfor:

[0164] .

[0165] (2) Thermal deformation rotation matrix R of the forward-looking ground camera measurement coordinate system C1 :

[0166] Parallel light beams (the seventh and eighth beams) at a certain angle pass through the forward-looking ground camera 9, forming a pair of light spots (the third and fourth spots) at the focal plane. The monitoring vector of the forward-looking ground camera's measurement coordinate system is constructed using the seventh and eighth beams, where the monitoring vector of the seventh beam at the reference time is v. aC10 The seventh beam monitoring vector at the measurement time is represented as v. aC11 The eighth beam monitoring vector at the reference time is v. bC10 The eighth beam monitoring vector at the measurement time is represented as v. bC11 Let the pixel size of the focal plane of the forward-looking ground camera be μ. C1 The focal length of the forward-looking ground camera 9 is F. C1 The coordinates of the CMOS origin in the forward-looking camera measurement coordinate system are (X... CC1 ,Y CC1 ,-F C1 The centroid coordinates of the third and fourth light spots at the reference time, respectively, in the forward-looking camera CMOS coordinate system are (X... aC10 ,Y aC10 ), (X bC10 ,Y bC10 Then, the reference time space vector of the seventh beam under the initial standard state in star camera 5 can be calculated. and the reference time space vector of the eighth beam under Star Camera 5 :

[0167] ;

[0168] ;

[0169] Changes in environmental conditions cause deformation of the forward-looking ground camera 9, resulting in a change in the centroid of the measurement spot. Therefore, the coordinates of the forward-looking ground camera 9 in the CMOS system at the measurement moment are (X...). aC11 ,Y aC11 ), (X bC11 ,Y bC11 The space vector of the seventh beam measured by the forward-looking camera 9. and the space vector of the measurement time of the eighth beam under the forward-looking camera 9 for:

[0170] ;

[0171] ;

[0172] By using the normalized cross product and calculating the projection of the three-axis vectors corresponding to the plane determined by the two vectors of the measurement time and the standard time into the forward-looking ground camera measurement coordinate system, the first rotation matrix M corresponding to the spatial vector of the reference time in the forward-looking ground camera measurement coordinate system is constructed. 0C1 The second rotation matrix M corresponding to the space vector at the measurement time. 1C1 The results are shown below:

[0173] ;

[0174] ;

[0175] The thermal deformation rotation matrix R of the forward-looking ground camera measurement coordinate system at the measurement time is then... C1 for:

[0176] .

[0177] (3) Thermal deformation rotation matrix R of the rear-view ground camera measurement coordinate system C2 :

[0178] Parallel light beams at a certain angle (the ninth and tenth beams) pass through the rear-view camera 12 and form a pair of light spots (the fifth and sixth spots) at the focal plane. The monitoring vector of the rear-view camera's measurement coordinate system is constructed using the ninth and tenth beams, where the monitoring vector of the ninth beam at the reference time is v. aC20 The ninth beam monitoring vector at the measurement time is represented as v. aC21 The tenth beam monitoring vector at the reference time is v. bC20 The measurement time is represented by the monitoring vector of the tenth beam as v. bC21 Let the pixel size of the rear-view ground-view camera 12 CMOS be μ. C2 The focal length of the optical system is F. C2 The coordinates of the origin of the rear-view camera's CMOS coordinate system in the rear-view camera's measurement coordinate system are (X... CC2 ,Y CC2 ,-F C2 The centroid coordinates of the fifth and sixth light spots at the reference time in the CMOS coordinate system of the rear-view camera are (X... aC20 ,Y aC20 (X) bC20 ,Y bC20 Then, the spatial vector of the ninth beam in the rear-view camera measurement coordinate system at the reference time can be calculated. The spatial vector of the tenth beam in the rear-view camera measurement coordinate system :

[0179] ;

[0180] ;

[0181] Changes in environmental conditions cause deformation of the forward-looking ground camera 9, resulting in a change in the centroid of the measurement spot. Therefore, the coordinates of the rear-looking ground camera in the CMOS coordinate system at the measurement moment are (X...). aC21 ,Y aC21 ), (X bC21 ,Y bC21 The spatial vector of the ninth beam in the rear-view camera measurement coordinate system at the measurement moment. The spatial vector of the tenth beam in the rear-view camera measurement coordinate system Represented as:

[0182] ;

[0183] ;

[0184] The first rotation matrix M, corresponding to the reference time spatial vector in the back-view ground camera measurement coordinate system, is calculated using the normalized cross product and the standard time. 0C2 The second rotation matrix M corresponding to the space vector at the measurement time. 1C2 :

[0185] ;

[0186] ;

[0187] The thermal deformation rotation matrix R of the rear-view camera 12 coordinate system at the measurement time C2 for:

[0188] .

[0189] In some embodiments, in step S4, the real-time rotation matrix from the forward-looking ground camera coordinate system to the star camera coordinate system is calculated by combining the thermal deformation matrices of the star camera coordinate system, the forward-looking ground camera measurement coordinate system, and the backward-looking ground camera measurement coordinate system at the measurement time using the following formula. And the real-time rotation matrix from the rear-view ground camera measurement coordinate system to the star camera coordinate system. :

[0190] ;

[0191] in, Let be the transpose of the thermal deformation matrix in the star camera coordinate system. The rotation matrix from the forward-looking ground camera coordinate system to the star camera coordinate system at the reference time. The rotation matrix from the back-view ground camera coordinate system to the star camera coordinate system at the reference time. The thermal deformation matrix of the coordinate system for the forward-looking ground camera measurement. The thermal deformation matrix of the measurement coordinate system for the rear-view ground camera.

[0192] It should be noted that the rotation matrix from the forward-looking ground camera coordinate system to the star camera coordinate system at the measurement time is constructed by combining the calibration results with the rotation matrices obtained from the three monitoring optical paths. Rotation matrix from the rear-view ground camera measurement coordinate system to the star camera coordinate system .

[0193] In some embodiments, in step S5, the rotation matrix from the star camera coordinate system to the inertial coordinate system is obtained based on the QUEST algorithm. The absolute pointing vector of the line of sight of the forward-looking camera 9 in the inertial coordinate system J2000 is calculated using the following formula. And the absolute pointing vector of the line of sight of the rear-view camera 12 in the inertial coordinate system J2000. :

[0194] ;

[0195] in, The real-time rotation matrix from the forward-looking ground camera coordinate system to the star camera coordinate system. The real-time rotation matrix from the rear-view ground camera coordinate system to the star camera coordinate system. Let be the unit vector of the line of sight of forward-looking camera 9 in the forward-looking camera measurement coordinate system. Let be the unit vector of the line of sight of the rear-view camera 12 in the rear-view camera measurement coordinate system.

[0196] It should be noted that during the measurement, star image information was acquired through celestial imaging. After star image matching, the unit vectors of the star images in the inertial coordinate system and the star camera 5 (attitude sensor) coordinate system were determined respectively. The rotation matrix from the star camera coordinate system to the inertial coordinate system was obtained based on the QUEST algorithm, and finally, the absolute pointing vectors of the front and rear camera line axes in the inertial coordinate system J2000 were determined accordingly. .

[0197] In some embodiments, in step S5, the absolute pointing vector of the line of sight of the forward-looking camera 9 in the inertial coordinate system J2000 is used. The absolute pointing vector of the line of sight of the rear-view camera 12 in the inertial coordinate system J2000. The angle between the line of sight of the forward-looking ground camera 9 and the line of sight of the rear-looking ground camera 12 is calculated using the following formula. :

[0198] .

[0199] It should be emphasized that the inertial coordinate system used in this invention is the J2000 inertial coordinate system.

[0200] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0201] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A monitoring system for mapping the angle between the forward and rearward viewing boresight axes of a camera and the absolute pointing, characterized by: The monitoring system comprises a collimated extended beam light source, a light-splitting reference prism, a first light-splitting module, a first mirror, a star camera, a second light-splitting module, a third light-splitting module, a fourth light-splitting module, a second mirror, a forward-looking ground camera, a third mirror and a backward-looking ground camera. The first light-splitting module, the second light-splitting module, the third light-splitting module and the fourth light-splitting module can be a Dammann grating, a dichroic mirror or a half-mirror.

2. The monitoring system of the angle between the front and rear view visual axes of a survey camera and the absolute pointing according to claim 1, characterized in that: The method comprises the following steps:

3. A monitoring method for measuring the included angle between the forward and rearward view axes of a mapping camera and the absolute pointing direction, implemented by using the monitoring system for measuring the included angle between the forward and rearward view axes of a mapping camera and the absolute pointing direction according to claim 1 or 2, characterized in that: S1: The star camera, the forward-looking ground camera and the backward-looking ground camera simultaneously image the sky by side swinging of the satellite platform, and a time point of imaging the sky is calibrated as a reference time point, so as to obtain an attitude matrix of the star camera coordinate system, a forward-looking ground camera measurement coordinate system and a backward-looking ground camera measurement coordinate system in the inertial coordinate system J2000, a unit vector of the visual axis of the forward-looking ground camera in the forward-looking ground camera measurement coordinate system, a unit vector of the visual axis of the backward-looking ground camera in the backward-looking ground camera measurement coordinate system, coordinate values of the center of mass of the first light spot and the second light spot in the star camera CMOS coordinate system, coordinate values of the center of mass of the third light spot and the fourth light spot in the forward-looking ground camera CMOS coordinate system, and coordinate values of the center of mass of the fifth light spot and the sixth light spot in the backward-looking ground camera CMOS coordinate system; S2: Based on step S1, a rotation matrix of the forward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time point and a rotation matrix of the backward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time point are calculated; S3: A working time point of the monitoring system after the reference time point is defined as a measurement time point; based on the center of mass coordinates of the light spots at the reference time point and the measurement time point, and in combination with the optical parameters of the star camera, the forward-looking ground camera and the backward-looking ground camera, a thermal deformation matrix of the star camera coordinate system, the forward-looking ground camera measurement coordinate system and the backward-looking ground camera measurement coordinate system at the measurement time point is calculated; S4: Based on the thermal deformation matrix of the star camera coordinate system, the forward-looking ground camera measurement coordinate system and the backward-looking ground camera measurement coordinate system at the measurement time point, a real-time rotation matrix of the forward-looking ground camera measurement coordinate system to the star camera coordinate system and a real-time rotation matrix of the backward-looking ground camera measurement coordinate system to the star camera coordinate system are obtained. ​ S5: calculating the rotation matrix of the star camera coordinate system to the inertial coordinate system J2000 based on the QUEST algorithm, combining the real-time rotation matrix of the forward-looking ground camera measurement coordinate system to the star camera coordinate system and the real-time rotation matrix of the backward-looking ground camera measurement coordinate system to the star camera coordinate system, obtaining the absolute pointing vector of the forward-looking ground camera's visual axis in the inertial coordinate system J2000 and the absolute pointing vector of the backward-looking ground camera's visual axis in the inertial coordinate system J2000, and performing inverse cosine calculation on the two absolute pointing vectors to obtain the angle between the visual axis of the forward-looking ground camera and the visual axis of the backward-looking ground camera at the measurement time.

4. The method of claim 3, wherein: The star camera coordinate system is a three-dimensional coordinate system with the projection center of the star camera as the origin, the Z-axis of the star camera coordinate system coincides with the optical axis direction of the star camera, the X-axis of the star camera coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the star camera, and the Y-axis of the star camera coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the star camera; The forward-looking ground camera measurement coordinate system is a three-dimensional coordinate system with the projection center of the forward-looking ground camera as the origin, the Z-axis of the forward-looking ground camera measurement coordinate system coincides with the optical axis of the forward-looking ground camera, the X-axis of the forward-looking ground camera measurement coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the forward-looking ground camera, and the Y-axis of the forward-looking ground camera measurement coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the forward-looking ground camera; The backward-looking ground camera measurement coordinate system is a three-dimensional coordinate system with the projection center of the backward-looking ground camera as the origin, the Z-axis of the backward-looking ground camera measurement coordinate system coincides with the optical axis of the backward-looking ground camera, the X-axis of the backward-looking ground camera measurement coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the backward-looking ground camera, and the Y-axis of the backward-looking ground camera measurement coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the backward-looking ground camera; The star camera CMOS coordinate system is a two-dimensional coordinate system with the center of the focal plane of the star camera as the origin, the X-axis of the star camera CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the star camera, and the Y-axis of the star camera CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the star camera; The forward-looking ground camera CMOS coordinate system is a two-dimensional coordinate system with the center of the focal plane of the forward-looking ground camera as the origin, the X-axis of the forward-looking ground camera CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the forward-looking ground camera, and the Y-axis of the forward-looking ground camera CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the forward-looking ground camera; The backward-looking ground camera CMOS coordinate system is a two-dimensional coordinate system with the center of the focal plane of the backward-looking ground camera as the origin, the X-axis of the backward-looking ground camera CMOS coordinate system is parallel to the horizontal pixel arrangement direction of the focal plane of the backward-looking ground camera, and the Y-axis of the backward-looking ground camera CMOS coordinate system is parallel to the vertical pixel arrangement direction of the focal plane of the backward-looking ground camera.

5. The method of claim 3, wherein: In step S2, the rotation matrix of the forward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time and the rotation matrix of the backward-looking ground camera measurement coordinate system to the star camera coordinate system at the reference time are calculated using the following formula: ； wherein, Rf is a rotation matrix of the forward-looking terrestrial camera measurement coordinate system to the star camera coordinate system at the reference time instant, Rr is a rotation matrix of the rearward-looking terrestrial camera measurement coordinate system to the star camera coordinate system at the reference time instant, C is an attitude matrix of the star camera coordinate system in the inertial coordinate system J2000, Cf is an attitude matrix of the forward-looking terrestrial camera measurement coordinate system in the inertial coordinate system J2000, Cr is an attitude matrix of the rearward-looking terrestrial camera measurement coordinate system in the inertial coordinate system J2000.

6. The method of claim 3, wherein: In step S3, the thermal deformation rotation matrix of the star camera coordinate system at the measurement moment is calculated based on the thermal deformation rotation matrix calculation method according to the coordinate values of the centroid of the first light spot and the centroid of the second light spot in the star camera CMOS coordinate system respectively and the optical parameters of the star camera; The thermal deformation rotation matrix of the forward-looking terrestrial camera measurement coordinate system at the measurement moment is calculated based on the thermal deformation rotation matrix calculation method according to the coordinate values of the centroid of the third light spot and the centroid of the fourth light spot in the forward-looking terrestrial camera CMOS coordinate system respectively and the optical parameters of the forward-looking terrestrial camera; The thermal deformation rotation matrix of the backward-looking terrestrial camera measurement coordinate system at the measurement moment is calculated based on the thermal deformation rotation matrix calculation method according to the coordinate values of the centroid of the fifth light spot and the centroid of the sixth light spot in the backward-looking terrestrial camera CMOS coordinate system respectively and the optical parameters of the backward-looking terrestrial camera.

7. The method of claim 6, wherein: The specific steps for calculating the thermal deformation rotation matrix of the star camera coordinate system at the measurement moment based on the thermal deformation rotation matrix calculation method according to the coordinate values of the centroid of the first light spot and the centroid of the second light spot in the star camera CMOS coordinate system respectively and the optical parameters of the star camera are as follows: The focal length of the star camera is Fs, and the pixel length on the focal plane of the star camera is μ S , the coordinates of the star camera CMOS coordinate system origin in the star camera coordinate system are (X CS ,Y CS ,-F S ) The coordinates of the centroid of the first light spot in the star camera CMOS coordinate system at the reference time are (X as0 ,Y as0 ), and the coordinates of the centroid of the second light spot in the star camera CMOS coordinate system are (X bs0 ,Y bs0 ). At the reference moment, based on the optical parameters of the star camera, the centroid coordinates of the first light spot and the centroid coordinates of the second light spot in the star camera CMOS coordinate system, the corresponding calculation of the third light beam in the star camera at the reference moment space vector and the fourth light beam in the star camera at the reference moment space vector : ； ； wherein, is the X coordinate of the star camera CMOS coordinate system origin in the star camera coordinate system, is the Y coordinate of the star camera CMOS coordinate system origin in the star camera coordinate system; At the measuring moment, the star camera deformation causes the displacement of the positions of both the first light spot and the second light spot, and the coordinates of the centroid of the first light spot in the CMOS coordinate system are (X as1 ,Y as1 ), and the coordinates of the centroid of the second light spot in the CMOS coordinate system are (X bs1 ,Y bs1 ). At the measurement moment, based on the optical parameters of the star camera, the centroid coordinates of the first light spot and the centroid coordinates of the second light spot in the star camera CMOS coordinate system, the corresponding calculation of the third light beam in the star camera at the measurement moment space vector and the fourth light beam in the star camera at the measurement moment space vector : ； ； wherein, Xstar is the X coordinate of the origin of the CMOS coordinate system in the star camera coordinate system, Ystar is the Y coordinate of the origin of the CMOS coordinate system in the star camera coordinate system; A first rotation matrix M corresponding to the space vector of the reference time instant in the astrocamera coordinate system is calculated by the following formula 0S and a second rotation matrix M corresponding to the space vector of the measurement time instant 1S : ； ； Based on the first rotation matrix M 0S and the second rotation matrix M 1S , a thermal deformation rotation matrix R S of the star camera coordinate system at the measurement moment is calculated 。 8. The method of claim 3, wherein: In step S4, the real-time rotation matrix of the forward-looking terrestrial camera measurement coordinate system to the star camera coordinate system is calculated by combining the thermal deformation matrix of each of the star camera coordinate system, the forward-looking terrestrial camera measurement coordinate system and the rear-looking terrestrial camera measurement coordinate system at the measurement time, through the following formula And the real-time rotation matrix of the rear-looking terrestrial camera measurement coordinate system to the star camera coordinate system : ； wherein is the transpose of the thermal deformation matrix of the star camera coordinate system, is the rotation matrix of the forward-looking terrestrial camera measurement coordinate system to the star camera coordinate system at the reference time instant, is the rotation matrix of the rearward-looking terrestrial camera measurement coordinate system to the star camera coordinate system at the reference time instant, is the thermal deformation matrix of the forward-looking terrestrial camera measurement coordinate system, is the thermal deformation matrix of the rearward-looking terrestrial camera measurement coordinate system.

9. The method of claim 8, wherein: In step S5, the rotation matrix of the star camera coordinate system to the inertial coordinate system is obtained based on the QUEST algorithm and the absolute pointing vector of the forward-looking camera in the inertial coordinate system J2000 is calculated by the following formula and the absolute pointing vector of the rear-looking camera in the inertial coordinate system J2000 is calculated by the following formula : ； wherein, Rf is a real-time rotation matrix of the forward-looking terrestrial camera measurement coordinate system to the star camera coordinate system, Rr is a real-time rotation matrix of the rearward-looking terrestrial camera measurement coordinate system to the star camera coordinate system, is a unit vector of the forward-looking terrestrial camera's boresight in the forward-looking terrestrial camera measurement coordinate system, is a unit vector of the rearward-looking terrestrial camera's boresight in the rearward-looking terrestrial camera measurement coordinate system.

10. The method of claim 9, wherein: In step S5, the absolute pointing vector of the forward-looking camera's optical axis in the inertial frame J2000 and the absolute pointing vector of the rearward-looking camera's optical axis in the inertial frame J2000 are calculated, by the following formula : 。

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