A star identification method applied to deep space large field of view high distortion image

Abstract

This invention relates to the field of astronomical navigation technology, specifically a star identification method applied to deep-space, large-field-of-view, high-distortion images. The method includes: Step 1, applying precession and nutation corrections to a standard star catalog based on the image imaging time, removing noise and dark current from the image itself, calculating the brightness index of observed stars in the image, and selecting the brightest star closest to the center region as the reference star; Step 2, filtering surrounding neighboring stars based on the central bright star, constructing a brightness sequence ring model including star spacing and brightness order, and quickly matching to filter out possible corresponding candidate star pairs; Step 3, extending the candidate star pairs into the longest possible continuous matching sequence by gradually expanding the most matching star points, prioritizing the retention of the longest matching chain with smooth extension; then checking whether these sequences can close end-to-end. If they can close, they are considered a correct match; if they cannot close, the most reasonable matching result is selected based on the sequence length.

Description

Technical Field

[0001] This invention relates to the field of astronomical navigation technology, specifically a method for star identification applied to deep-space, large-field-of-view, high-distortion images. Background Technology

[0002] Due to the constraints of the positions of the ground and the deep space probe, the ground-based tracking and control time for the deep space probe is limited. In deep space exploration missions, the distance between the probe and the ground is extremely vast. The signal transmission delay caused by this distance prevents the ground-based tracking and control system from providing real-time navigation information to the probe. Therefore, deep space probes need to possess a certain degree of autonomous navigation and positioning capabilities. The information available in deep space for autonomous navigation and positioning is the widely distributed stellar information whose positions do not shift significantly in a short period. This necessitates stellar identification algorithms that can compare the star images captured by the probe with a full-sky star map to determine the information of the observed stars.

[0003] As a key technology in deep space exploration, star recognition algorithms directly impact the positioning accuracy and attitude calculation accuracy of probes. The most widely used and mature star recognition algorithm is the triangle algorithm, which forms the basis of many other star recognition algorithms. However, the triangle algorithm and its derivatives are prone to mismatches in images with large fields of view and irregular distortion distributions. This is because star matching algorithms are based on star-to-star diagonal distances. In images with large fields of view and irregular distortion distributions, the angular distance error between the star image point angular distance information and the actual diagonal distance formed by the corresponding navigation star becomes unpredictable, easily leading to mismatches in the absence of sufficient constraints. Using multiple star-to-star diagonal distance constraints for pattern matching can effectively overcome the mismatch problem caused by large field-of-view, high-distortion images, but the resulting increase in recognition time limits its application outside of experiments. Therefore, how to utilize multiple star-to-star diagonal distance constraints while keeping the matching time within an acceptable range has significant practical application value. Summary of the Invention

[0004] The purpose of this invention is to provide a star identification method for deep-space, large-field-of-view, high-distortion images, in order to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A star identification method for deep-space, large-field-of-view, high-distortion images, characterized by comprising the following steps: Step 1: After precession and nutation corrections are applied to the standard star catalog based on the image imaging time, noise and dark current are removed from the image itself, and the brightness index of the observed stars in the image is calculated. The observed star with the highest brightness and closest to the center region is selected as the reference star. Step 2: Based on the central bright star, filter the surrounding neighboring stars and construct a brightness sequence ring model that includes the star spacing and brightness order. Then, quickly match and filter out possible corresponding candidate star pairs. Step 3: By gradually expanding the idea of ​​the best matching star point, extend the longest continuous matching sequence from the candidate star pair, and prioritize retaining the matching chain with the smooth extension and the longest matching sequence; then check whether these sequences can be closed at the beginning and end. If they can be closed, they are considered to be a correct match. If they cannot be closed, select the most reasonable matching result based on the sequence length.

[0006] Preferably, step 1 specifically includes: Step 1.1: Calculate the Julian century number based on the image imaging time, and then use the Julian century number to perform precession and nutation corrections; Step 1.2: Calculate the grayscale integral value of all star points from the star map by summing the pixel grayscale values ​​of the observation point spot area. Use this value as the brightness index of the observed star points and select the brightest star as the candidate reference star. If there are multiple candidate stars with similar brightness, select the star closest to the center of the field of view as the reference star, number it 0, and establish a polar coordinate system with the position of this star as the origin.

[0007] Preferably, step 2 specifically includes: Step 2.1: Filter nearby satellites around the reference star. The neighboring stars are arranged in counterclockwise azimuth angles to form a brightness sequence ring model, and numbered from 1 to n; Step 2.2: Match the angular distance and brightness relationship between the reference star and neighboring stars with the star-to-star angular distance index table: Step 2.3: Based on the matched reference star navigation star identifiers, extract the angular distance and magnitude information of its theoretical neighboring stars from the index table to generate a candidate set of neighboring stars to be matched, denoted as . to .

[0008] Preferably, step 2.1 specifically includes: Extract the following features: Relationship between reference star and neighboring stars: Record the angular distance between the reference star and each neighboring star, and mark the brightness relationship; Neighboring star relationships: Calculate the angular distance between adjacent star pairs and their brightness ranking; Global brightness sorting: The neighboring stars are sorted by brightness.

[0009] Preferably, step 2.2 specifically includes: Retrieve star pairs from the index table that meet the following conditions: (1); In formula (1) Represents the angular distance in the star diagonal distance index table. Number its star pairs. This represents the angular distance between the reference star and the neighboring star numbered x. Indicates the matching threshold; Ruoxing The magnitude relationship is ,but For the reference star, candidate matching asterisks are identified. The frequency of occurrence of all candidate matching asterisks is counted, and the most frequently occurring asterisk is selected as the reference star navigation asterisk, denoted as . .

[0010] Preferably, step 3 specifically includes: Step 3.1: Apply dual constraints to the angular distance and brightness relationships between neighboring stars: Step 3.2: By weighted fusion of chain length features and brightness ranking relationship, the optimal matching chain that has both geometric continuity and physical consistency is selected.

[0011] Preferably, step 3.1 specifically includes: Brightness ranking consistency: The brightness ranking of observed neighboring stars must be consistent with the magnitude ranking of candidate navigation stars; Angular distance chain matching: The observed angular distances of adjacent star pairs must match the angular distances of candidate navigation star pairs, and the cumulative error must not exceed a threshold. (2); In formula (2) express One of the candidate navigation stars and The diagonal distance between a candidate navigation satellite in the system. This represents the angular distance between neighboring stars numbered a and b.

[0012] Preferably, step 3.2 specifically includes: The final score for the matching chain is calculated as follows: (3); in Indicates the chain length score weight. The score represents the length of the matching chain. This represents the brightness consistency score.

[0013] Preferably, the matching chain length fraction The calculation method is as follows: (4); in This represents the number of consecutively matched adjacent star pairs in the candidate chain. The theoretical maximum chain length is represented by the number of neighboring stars in the bright-sequence ring model. Decide: (5).

[0014] Preferably, the brightness relationship consistency score The calculation is performed at two levels: local and global. The local level is sorted by adjacent star pairs, while the global level is sorted by the overall order. Local Hierarchical Score The brightness order matching degree of adjacent star pairs is obtained by calculating the brightness order matching degree of adjacent star pairs, and the consistency between the brightness order of adjacent navigation star pairs in the candidate chain and the original brightness sequence ring model is statistically analyzed. (6); in As a consistency parameter, when the brightness relationship of corresponding star pairs in the brightness sequence ring model is consistent with the magnitude relationship of the navigation stars at both ends of the chain... =1, otherwise =0; Global Hierarchical Score The candidate chains forming the closed loop are compared with the global brightness relationship of the brightness sequence ring model to check whether the overall brightness ranking of the navigation stars is consistent with the original brightness sequence ring model. (7); Brightness Relationship Consistency Score Local hierarchical scores Global Hierarchical Score Joint decision: (8); in For hierarchical weights; After the neighboring star matching verification is completed, the candidate navigation star pairs form a chain structure of a certain length. The optimal candidate chain is selected from the chain structure to become the matching chain for star map recognition. The navigation star points in the matching chain are matched one by one with the points to be matched, thereby completing the star map recognition work.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a star identification method for deep-space, large-field-of-view, high-distortion images. It constructs local feature descriptions through brightness optimization of the central star and geometric encoding (angular distance and brightness ranking) of a ring-shaped neighborhood structure. Combined with a matching strategy using a star pair angular distance index table, it prioritizes candidate star pairs that meet both brightness and geometric constraints. Furthermore, based on the longest continuous matching chain optimization mechanism, it solves the problem of mismatched star points under positional distortion interference, effectively improving the efficiency of star identification. This invention fully utilizes the relationships between stars as constraints, enhances noise resistance through brightness ranking, and ensures matching reliability through closed-loop / open-chain compatibility verification of the ring topology. It is suitable for complex observation scenarios with significant star point positioning deviations or partial occlusion. Simultaneously, the use of constraints effectively reduces the matching time in star map identification, improving the efficiency of star identification. Attached Figure Description

[0016] Figure 1 A flowchart of a star identification method for deep-space large-field-of-view, high-distortion images provided by the present invention; Figure 2 This is a schematic diagram of the brightness sequence ring model in this invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Figure 1 This is a flowchart illustrating a star identification method for deep-space, large-field-of-view, high-distortion images provided by the present invention. Figure 1 As shown, the embodiments of the present invention provide a star identification method applied to deep-space large field-of-view high-distortion images, including the following steps: Step 1: After precession and nutation corrections are applied to the standard star catalog based on the image imaging time, noise and dark current are removed from the image itself, and the brightness index of the observed stars in the image is calculated. The observed star with the highest brightness and closest to the center region is selected as the reference star. Step 2: Based on the central bright star, filter the surrounding neighboring stars and construct a brightness sequence ring model that includes the star spacing and brightness order. Then, quickly match and filter out possible corresponding candidate star pairs. Step 3: By gradually expanding the idea of ​​the best matching star point, extend the longest continuous matching sequence from the candidate star pair, and prioritize retaining the matching chain with the smooth extension and the longest matching sequence; then check whether these sequences can be closed at the beginning and end. If they can be closed, they are considered to be a correct match. If they cannot be closed, select the most reasonable matching result based on the sequence length.

[0019] In one embodiment of the present invention, step 1 specifically includes: Step 1.1: Calculate the Julian century number based on the image imaging time, and then use the Julian century number to perform precession and nutation corrections; Step 1.2: Calculate the grayscale integral value of all star points from the star map by summing the pixel grayscale values ​​of the observation point spot area. Use this value as the brightness index of the observed star points and select the brightest star as the candidate reference star. If there are multiple candidate stars with similar brightness, select the star closest to the center of the field of view as the reference star, number it 0, and establish a polar coordinate system with the position of this star as the origin.

[0020] Figure 2 This is a schematic diagram of the bright sequence loop model in this invention. In one embodiment of this invention, step 2 specifically includes: Step 2.1: Filter nearby satellites around the reference star. The neighboring stars are arranged in counterclockwise azimuth angles to form a brightness sequence ring model, and numbered from 1 to n; Step 2.2: Match the angular distance and brightness relationship between the reference star and neighboring stars with the star-to-star angular distance index table: Step 2.3: Based on the matched reference star navigation star identifiers, extract the angular distance and magnitude information of its theoretical neighboring stars from the index table to generate a candidate set of neighboring stars to be matched, denoted as . to For example, it may contain asterisks [678,416, 432, 345], indicating that these navigation stars may correspond to the observed star No. 2.

[0021] Furthermore, in one embodiment of the present invention, step 2.1 specifically includes: Extract the following features: Relationship between reference star and neighboring stars: Record the angular distance between the reference star and each neighboring star, and mark the brightness relationship; for example, "1" indicates that the reference star is brighter than the neighboring stars, and "0" indicates that it is dimmer; Neighboring star relationships: Calculate the angular distance between adjacent star pairs and their brightness ranking; if the status indicator between star 2 and star 3 is "1", it means that star 2 is brighter than star 3, and the indicator is "0", it means that star 2 is dimmer than star 3; Global brightness sorting: The neighboring stars are sorted by brightness. For example, in a region containing only 4 stars, "3-1-2-4" means that star 3 is the brightest and star 4 is the dimmest.

[0022] In one embodiment of the present invention, step 2.2 specifically includes: Retrieve star pairs from the index table that meet the following conditions: (1); In formula (1) Represents the angular distance in the star diagonal distance index table. Number its star pairs. This represents the angular distance between the reference star and the neighboring star numbered x. Indicates the matching threshold; Ruoxing The magnitude relationship is (represent Compare (bright), then For the reference star, candidate matching asterisks are identified. The frequency of occurrence of all candidate matching asterisks is counted, and the most frequently occurring asterisk is selected as the reference star navigation asterisk, denoted as . .

[0023] In one embodiment of the present invention, step 3 specifically includes: Step 3.1: Apply dual constraints to the angular distance and brightness relationships between neighboring stars: Step 3.2: By weighted fusion of chain length features and brightness ranking relationship, the optimal matching chain that has both geometric continuity and physical consistency is selected.

[0024] In one embodiment of the present invention, step 3.1 specifically includes: Brightness ranking consistency: The brightness ranking of observed neighboring stars must be consistent with the magnitude ranking of candidate navigation stars; Angular distance chain matching: The observed angular distances of adjacent star pairs must match the angular distances of candidate navigation star pairs, and the cumulative error must not exceed a threshold. (2); In formula (2) express One of the candidate navigation stars and The diagonal distance between a candidate navigation satellite in the system. This represents the angular distance between neighboring stars numbered a and b.

[0025] Based on the advantages of spatial continuity assessment using standardized chain length scores, the matching degree between adjacent star pairs and the global brightness order is calculated hierarchically. Local noise interference and overall misalignment risk are balanced by dynamic weights. Finally, the matching confidence is quantified by comprehensive score, ensuring that high-quality candidate chains that meet the brightness sequence ring structure constraints are selected first in complex observation environments.

[0026] In one embodiment of the present invention, step 3.2 specifically includes: The final score for the matching chain is calculated as follows: (3); in Indicates the chain length score weight. The score represents the length of the matching chain. This represents the brightness consistency score.

[0027] In one embodiment of the present invention, the matching chain length fraction The calculation method is as follows: (4); in This represents the number of consecutively matched adjacent star pairs in the candidate chain. The theoretical maximum chain length is represented by the number of neighboring stars in the bright-sequence ring model. Decide: (5).

[0028] In one embodiment of the present invention, the brightness relationship consistency score The calculation is performed at two levels: local and global. The local level is sorted by adjacent star pairs, while the global level is sorted by the overall order. Local Hierarchical Score The brightness order matching degree of adjacent star pairs is obtained by calculating the brightness order matching degree of adjacent star pairs, and the consistency between the brightness order of adjacent navigation star pairs in the candidate chain and the original brightness sequence ring model is statistically analyzed. (6); in As a consistency parameter, when the brightness relationship of corresponding star pairs in the brightness sequence ring model is consistent with the magnitude relationship of the navigation stars at both ends of the chain... =1, otherwise =0; Global Hierarchical Score The candidate chains forming the closed loop are compared with the global brightness relationship of the brightness sequence ring model to check whether the overall brightness ranking of the navigation stars is consistent with the original brightness sequence ring model. (7); Brightness Relationship Consistency Score Local hierarchical scores Global Hierarchical Score Joint decision: (8); in For hierarchical weights; After the neighboring star matching verification is completed, the candidate navigation star pairs form a chain structure of a certain length. The optimal candidate chain is selected from the chain structure to become the matching chain for star map recognition. The navigation star points in the matching chain are matched one by one with the points to be matched, thereby completing the star map recognition work.

[0029] The feasibility of the star identification method for deep-space, large-field-of-view, high-distortion images provided by this invention is verified using specific data: This invention uses image data from a certain deep space test payload as test data. The image data includes a TIFF image and the initial interior orientation elements of the image. The right ascension and declination of the center of the image are approximately [64.48, 20.05]. Step 1: Calculate the Julian century number according to the image imaging time, and then perform precession and nutation corrections on the star catalog accordingly. For example, [52.73374, 18.79942] is corrected to [52.73467, 18.79892]. Extract the star images from the image, resulting in a total of 34,164 star images. Select the brightest and closest observation star to the center region as the reference star. The coordinates of this reference star on the image are: [3071.349, 3172.095]. Step 2: Based on the central bright star, select surrounding neighboring stars and construct a brightness sequence ring model that includes the star spacing and brightness order. Through rapid matching, select possible corresponding candidate star pairs. The coordinates of the obtained ring structure on the image are: [2611.523, 2895.062], [2909.762, 2493.079], [3333.607, 3114.063], [3530.714, 3554.618]; Step 3: After the neighboring star matching verification is completed, the candidate navigation star pairs can form a chain structure of a certain length. The optimal candidate chain is selected from the chain structure to become the matching chain for star map recognition. The navigation star points in the matching chain are matched one by one with the points to be matched, thus completing the star map recognition work. Finally, the right ascension and declination coordinates of the corresponding stars in the ring structure are: [63.85895, 21.14201], [66.57787, 21.47017], [66.23882, 19.04177], [65.73449, 17.54232].

[0030] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for star identification applied to deep-space, large-field-of-view, high-distortion images, characterized in that, Includes the following steps: Step 1: After precession and nutation corrections are applied to the standard star catalog based on the image imaging time, noise and dark current are removed from the image itself, and the brightness index of the observed stars in the image is calculated. The observed star with the highest brightness and closest to the center region is selected as the reference star. Step 2: Based on the central bright star, filter the surrounding neighboring stars and construct a brightness sequence ring model that includes the star spacing and brightness order. Then, quickly match and filter out possible corresponding candidate star pairs. Step 3: By gradually expanding the idea of ​​the best matching star point, extend the longest continuous matching sequence from the candidate star pair, and prioritize retaining the matching chain with the smooth extension and the longest matching sequence; then check whether these sequences can be closed at the beginning and end. If they can be closed, they are considered to be a correct match. If they cannot be closed, select the most reasonable matching result based on the sequence length.

2. The star identification method for deep-space large field-of-view, high-distortion images as described in claim 1, characterized in that, Step 1 specifically includes: Step 1.1: Calculate the Julian century number based on the image imaging time, and then use the Julian century number to perform precession and nutation corrections; Step 1.2: Calculate the grayscale integral value of all star points from the star map by summing the pixel grayscale values ​​of the observation point spot area. Use this value as the brightness index of the observed star points and select the brightest star as the candidate reference star. If there are multiple candidate stars with similar brightness, select the star closest to the center of the field of view as the reference star, number it 0, and establish a polar coordinate system with the position of this star as the origin.

3. The star identification method for deep-space large field-of-view high-distortion images as described in claim 2, characterized in that, Step 2 specifically includes: Step 2.1: Filter nearby satellites around the reference star. The neighboring stars are arranged in counterclockwise azimuth angles to form a brightness sequence ring model, and numbered from 1 to n; Step 2.2: Match the angular distance and brightness relationship between the reference star and neighboring stars with the star-to-star angular distance index table: Step 2.3: Based on the matched reference star navigation star identifiers, extract the angular distance and magnitude information of its theoretical neighboring stars from the index table to generate a candidate set of neighboring stars to be matched, denoted as . to .

4. The star identification method for deep-space large field-of-view, high-distortion images as described in claim 3, characterized in that, Step 2.1 specifically includes: Extract the following features: Relationship between reference star and neighboring stars: Record the angular distance between the reference star and each neighboring star, and mark the brightness relationship; Neighboring star relationships: Calculate the angular distance between adjacent star pairs and their brightness ranking; Global brightness sorting: The neighboring stars are sorted by brightness.

5. A star identification method for deep-space, large-field-of-view, high-distortion images as described in claim 4, characterized in that, Step 2.2 specifically includes: Retrieve star pairs from the index table that meet the following conditions: （1）； In formula (1) Represents the angular distance in the star diagonal distance index table. Number its star pairs. This represents the angular distance between the reference star and the neighboring star numbered x. Indicates the matching threshold; Ruoxing The magnitude relationship is ,but For the reference star, candidate matching asterisks are identified. The frequency of occurrence of all candidate matching asterisks is counted, and the most frequently occurring asterisk is selected as the reference star navigation asterisk, denoted as . .

6. A star identification method for deep-space, large-field-of-view, high-distortion images as described in claim 5, characterized in that, Step 3 specifically includes: Step 3.1: Apply dual constraints to the angular distance and brightness relationships between neighboring stars: Step 3.2: By weighted fusion of chain length features and brightness ranking relationship, the optimal matching chain that has both geometric continuity and physical consistency is selected.

7. A star identification method for deep-space, large-field-of-view, high-distortion images as described in claim 6, characterized in that, Step 3.1 specifically includes: Brightness ranking consistency: The brightness ranking of observed neighboring stars must be consistent with the magnitude ranking of candidate navigation stars; Angular distance chain matching: The observed angular distances of adjacent star pairs must match the angular distances of candidate navigation star pairs, and the cumulative error must not exceed a threshold. （2）； In formula (2) express One of the candidate navigation stars and The diagonal distance between a candidate navigation satellite in the system. This represents the angular distance between neighboring stars numbered a and b.

8. A star identification method for deep-space, large-field-of-view, high-distortion images as described in claim 7, characterized in that, Step 3.2 specifically includes: The final score for the matching chain is calculated as follows: （3）； in Indicates the chain length score weight. The score represents the length of the matching chain. This represents the brightness consistency score.

9. A star identification method for deep-space, large-field-of-view, high-distortion images as described in claim 8, characterized in that, Matching chain length score The calculation method is as follows: （4）； in This represents the number of consecutively matching adjacent star pairs in the candidate chain. The theoretical maximum chain length is represented by the number of neighboring stars in the bright-sequence ring model. Decide: （5）。 10. A star identification method for deep-space, large-field-of-view, high-distortion images as described in claim 8, characterized in that, Brightness Relationship Consistency Score The calculation is performed at two levels: local and global. The local level is sorted by adjacent star pairs, while the global level is sorted by the overall order. Local Hierarchical Score The brightness order matching degree of adjacent star pairs is obtained by calculating the brightness order matching degree of adjacent star pairs, and the consistency between the brightness order of adjacent navigation star pairs in the candidate chain and the original brightness sequence ring model is statistically analyzed. （6）； in As a consistency parameter, when the brightness relationship of corresponding star pairs in the brightness sequence ring model is consistent with the magnitude relationship of the navigation stars at both ends of the chain... =1, otherwise =0; Global Hierarchical Score The candidate chains forming the closed loop are compared with the global brightness relationship of the brightness sequence ring model to check whether the overall brightness ranking of the navigation stars is consistent with the original brightness sequence ring model. （7）； Brightness Relationship Consistency Score Local hierarchical scores Global Hierarchical Score Joint decision: （8）； in For hierarchical weights; After the neighboring star matching verification is completed, the candidate navigation star pairs form a chain structure of a certain length. The optimal candidate chain is selected from the chain structure to become the matching chain for star map recognition. The navigation star points in the matching chain are matched one by one with the points to be matched, thereby completing the star map recognition work.

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