Optical load on-orbit calibration navigation star catalog construction method, calibration method and equipment

Abstract

The invention relates to the technical field of satellite optical load in-orbit calibration, in particular to an optical load in-orbit calibration navigation star catalogue construction method, a calibration method and equipment. According to the in-orbit calibration navigation star catalogue construction method, star magnitude and reference angular distance are set to screen alternative navigation star catalogues, the applicability of the navigation star catalogues is guaranteed, and meanwhile the distribution uniformity of navigation stars in the star catalogues is improved. For load application, a navigation star catalogue array is generated, all-sky-domain fixed stars are divided under a heliocentric inertial coordinate system, and the screened star catalogue is bound in a three-dimensional array form, so that software implementation and in-orbit application are facilitated. For satellite optical load on-orbit calibration, the problem of conversion from a navigation star catalogue to a load pointing target is solved, and the pointing target is easily and rapidly obtained according to the actual engineering requirement of the optical load to complete space calibration. The on-orbit calibration method is more convenient for on-orbit application, the optical load can point to a determined star catalogue to realize load calibration, and the calculation amount and flow of ground image processing are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of on-orbit calibration technology for satellite optical payloads, and in particular to a method for constructing an on-orbit calibration navigation satellite catalog, a calibration method, and equipment for optical payloads. Background Technology

[0002] For satellites using high-resolution visible light cameras as payloads, the imaging parameters of the payload cameras are all tested and set on the ground. After entering orbit, a lot of calibration work needs to be carried out to complete the optical parameter calibration in the outer space environment, so as to achieve high-resolution imaging of the earth at different orbital altitudes. However, with the improvement of satellite payload imaging accuracy, the traditional satellite payload camera on-orbit calibration work has the following problems: (1) For cameras with high accuracy and small field of view, the requirements for inertial sky areas for space calibration are extremely demanding. The previous calibration method pointing to any sky area cannot meet the requirements of high-resolution satellite payload characteristics. It is necessary to identify the sky area that can meet specific requirements. (2) After the satellite enters orbit, the camera needs to carry out calibration work frequently and irregularly. The traditional method of relying on ground calculation and then injecting calibration pointing information is not only complex in itself, but also easy to trigger on-board autonomous protection, resulting in calibration failure, which puts great pressure on ground telemetry and control, and is inefficient and cannot meet the requirements of the model mission. Summary of the Invention

[0003] The purpose of this invention is to propose a method for constructing an on-orbit calibration navigation satellite catalog for optical payloads, an on-orbit calibration method, electronic equipment, and a computer-readable storage medium, so as to construct an on-orbit calibration navigation satellite catalog for optical payloads and realize the autonomous real-time on-orbit calibration of satellite optical payloads.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a method for constructing an on-orbit calibration navigation satellite catalog for optical payloads, characterized by comprising the following steps: S1. Set the number W of navigation star catalogs used for calibration of the optical payload within the celestial sphere constructed in the heliocentric inertial coordinate system; S2. Select one spherical ring in the northern and southern hemispheres of the celestial sphere. The two spherical rings are symmetrical along the equator. Divide the two spherical rings into W / 2 celestial regions according to right ascension. Number each celestial region and store the navigation stars in these celestial regions into the first candidate navigation star library according to the partition. S3. The navigation stars in the first candidate navigation star library are screened again in terms of brightness and stability. Navigation stars that do not meet the requirements are removed, and navigation stars that meet the brightness and stability requirements are stored in the second navigation star library. S4. Calculate the angular distance between each navigation star in the second navigation star database and set a reference angular distance. Set the number of target navigation stars M in the sky region corresponding to the field of view of the optical payload. Let n be the number of navigation stars whose angular distance between navigation stars is within the set reference angular distance range. Determine whether n>M. If yes, identify all navigation stars that meet the reference angular distance range as candidate navigation star lists, number each candidate navigation star list according to the sky region it is located in, and store it in the first star list database. Otherwise, put it back into the first candidate navigation star database. S5. Extract the candidate navigation star catalogs in the first star catalog library according to the divided sky regions, so that each sky region corresponds to a navigation star catalog, and store it in the second star catalog library. S6. Calculate the right ascension and declination of the center points of all navigation star catalogs in the second star catalog library, and use them as imaging targets for optical payload calibration. S7. Define a three-dimensional array of navigation star catalogs, and bind the right ascension and declination of the center points of all navigation star catalogs in the second star catalog library to the three-dimensional array of navigation star catalogs.

[0005] Optionally, the filtering criteria in step S3 are: the star magnitude is within the range of [level1, level2], and the star attribute is identified as a non-binary star and a non-variable star navigation star.

[0006] Optionally, in step S5, candidate navigation star catalogs in the first star catalog library are extracted according to the divided sky regions, with each sky region corresponding to one navigation star catalog. The extraction principle is as follows: If more than one candidate navigation star catalog is selected for the same celestial region, the catalog with the most navigation stars is selected as the final navigation star catalog for that celestial region; if only one candidate navigation star catalog is selected for a celestial region, this catalog is selected as the navigation star catalog for that celestial region; if no candidate navigation star catalog is selected for a celestial region, the navigation star catalog from the adjacent celestial region with the smaller right ascension is selected as the navigation star catalog for that celestial region.

[0007] Optionally, if the number of sky regions for which no candidate navigation star catalogs are selected is greater than three, the declination width of the spherical ring is increased and steps S2 to S4 are repeated.

[0008] Secondly, the present invention also provides an on-orbit calibration method for optical payloads, comprising the following steps: a) Generate a three-dimensional array of navigation star catalogs using any of the methods described in the first aspect; b) Based on the spacecraft orbital parameters and the solar direction vector, select candidate star catalog center points from the three-dimensional array that meet the sunlight avoidance conditions. The sunlight avoidance conditions require that the angle between the sun and the pointing direction be greater than the safety threshold. c) Calculate the angular distance between the spacecraft's current position and each candidate center point, and select the target with the smallest angular distance; d) Control the attitude maneuver to point the optical payload toward the center point of the selected target.

[0009] In the second aspect, optionally, in step b, targets within ±15 degrees of the ecliptic plane of the celestial sphere are screened and excluded simultaneously.

[0010] In the second aspect, optionally, the safety threshold is the angle between the beveled edge of the optical load's shield and the optical axis of the optical load.

[0011] Thirdly, the present invention also provides an electronic device, comprising: Memory, used to store computer-readable instructions; and A processor for executing computer-readable instructions to perform a method of either the first aspect or the second aspect.

[0012] Fourthly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program is executed by a processor to implement any of the implementations of the first and second aspects.

[0013] The above-described technical solution of the present invention has the following advantages: The present invention provides a method for constructing an on-orbit calibration navigation star catalog for optical payloads. It establishes magnitude and reference angular distance to screen candidate navigation star catalogs, ensuring the applicability of the catalogs while improving the uniformity of navigation star distribution within the catalogs. For payload applications, it generates a navigation star catalog array and divides the entire sky into heliocentric inertial coordinates. The screened catalogs are bound in a three-dimensional array format, which facilitates software implementation and on-orbit application. For on-orbit calibration of satellite optical payloads, it solves the problem of converting the navigation star catalog to the payload's pointing target, allowing for rapid acquisition of the pointing target and completion of space calibration according to the actual engineering needs of the optical payload.

[0014] The on-orbit calibration method provided by this invention ensures the safety of the optical payload, avoids interference from sunlight at the pointed-to star catalog location, and can find the nearest star catalog target based on the spacecraft's position in the sky. The payload can point to the target through attitude maneuvers in the shortest possible time, and can be maneuvered to any target star catalog location that meets the payload safety requirements via commands from the ground, thus achieving the payload calibration task. Compared to traditional star-sensitive cataloging strategies that require matching and comparing imaging images with star catalogs on the ground to obtain calibration information, this application combines practical on-orbit applications, obtaining a star catalog library covering a specified sky area and generating the star catalog library as a three-dimensional array. Generating the star catalog library in array form makes it more convenient for on-orbit applications. The optical payload can point to a specific star catalog to achieve payload calibration, greatly reducing the computational load and process of ground image processing. Attached Figure Description

[0015] The accompanying drawings are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not be consistent with the actual product.

[0016] Figure 1 This is a flowchart of an on-orbit calibration navigation satellite catalog construction method for an optical payload according to an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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] like Figure 1 As shown, the method for constructing an on-orbit calibration navigation satellite catalog for optical payloads provided in this embodiment of the invention includes the following steps: S1. Based on mission requirements or experience, set the number W of navigation star catalogs used for calibration of the optical payload within the celestial sphere constructed in the heliocentric inertial coordinate system.

[0019] S2. Divide the celestial sphere into two hemispheres, the Northern Hemisphere corresponding to the celestial region with declination from 0° to 90°, and the Southern Hemisphere corresponding to the celestial region with declination from 0° to -90°. Select a spherical ring in each of the Northern and Southern Hemispheres, with the two spherical rings symmetrical along the equator. The Northern Hemisphere is selected... The sky region, as a spherical ring in the Northern Hemisphere, is selected from the Southern Hemisphere. The celestial region forms a spherical ring around the Southern Hemisphere. A positive number indicates the declination of the center point of the region. Used to characterize the extent of a region. The two spherical annulus are divided into P celestial regions according to right ascension, where P = W / 2, and the extent of right ascension is... The calculation formula is: Each celestial region is numbered. The P celestial regions of the spherical annulus in the Northern Hemisphere, where P = W / 2, are numbered according to their equatorial length, increasing from smallest to largest. Divide the spherical ring of the Southern Hemisphere into P regions, where P = W / 2, and number the regions according to their equatorial length, increasing from small to large. The navigation stars within these celestial regions are stored in the first candidate navigation star (StarTable1) according to their regions. Divide into sections.

[0020] S3. Based on step S2, star magnitudes are filtered. In this embodiment, navigation stars with magnitudes in the range of [level1, level2] are selected, and navigation stars that do not meet the requirements are removed. For example, navigation stars with star attributes identified as binary stars or variable stars in the star table are removed. Navigation stars that meet the brightness and stability requirements are stored in the second navigation star library (StarTable 2).

[0021] S4. Based on step S3, calculate the angular distances between each navigation satellite in the second navigation satellite pool and set a reference angular distance, selecting the reference angular distance as... ,in Let M be the field of view of the optical payload, and let n be the number of target navigation stars in the sky corresponding to the field of view of the optical payload. Let n be the number of navigation stars whose angular distances between navigation stars are within the set reference angular distance range. Determine whether n > M. If so, identify all navigation stars that meet the reference angular distance range as candidate navigation stars, denoted as . and , where subscript The first in the Northern Hemisphere The first region List of candidate navigation stars, subscript The first in the Southern Hemisphere The first region If a candidate navigation star list is generated, it is stored in the first star list library (Starlist1); otherwise, it is returned to the first candidate navigation star library (StarTable1).

[0022] S5. Extract candidate navigation star lists from the first star list library (Starlist1) according to the sky regions divided in step S2, so that each sky region corresponds to one navigation star list, and store them in the second star list library. In this embodiment, an example extraction principle is as follows: If more than one candidate navigation star catalog is selected for the same celestial region, the catalog with the most navigation stars is chosen as the final navigation star catalog for that region. If only one candidate navigation star catalog is selected for a celestial region, this catalog is used for that region. If no candidate navigation star catalog is selected for a celestial region, the navigation star catalog of the adjacent region with the smaller right ascension is chosen as the navigation star catalog for that region. For example, in the Northern Hemisphere... The final navigation star will be denoted as Starlib. Ni And so on, to obtain the sky region of the Northern Hemisphere. Group navigation star catalog; the first [number] of the Southern Hemisphere sky region The final navigation star will be denoted as Starlib. Si And so on, to obtain the southern hemisphere sky region Create a navigation star list and store all extracted navigation star lists into the second star list library (Starlist2).

[0023] S6. Calculate the right ascension and declination of the center points of all navigation star catalogs in the second star catalog (Starlist2), which will serve as imaging targets for optical payload calibration. For example, based on the navigation star catalog Starlib in the second star catalog (Starlist2)... Ni and Starlib Si , .

[0024] Calculate the navigation star table Starlib Ni The mean right ascension is the same as the right ascension of the center point of the navigation star catalog: ; Calculate the navigation star table Starlib Si mean right ascension That is, the right ascension of the center point of the navigation star catalog: ; Calculate the navigation star table Starlib Ni mean declination That is, the declination of the center point of the navigation star catalog: ; Calculate the navigation star table Starlib Si mean declination That is, the declination of the center point of the navigation star catalog: ; In the above formula, For the first The first in the navigation star list One navigation satellite, For the first Number of navigation stars in the navigation star table The first in the Northern Hemisphere The first in the navigation star list The right ascension of each navigation star, The first in the Southern Hemisphere The first in the navigation star list The right ascension of each navigation star, The first in the Northern Hemisphere The first in the navigation star list The declination of a navigation satellite, The first in the Southern Hemisphere The first in the navigation star list The declination of a navigation satellite, .

[0025] This completes the selection process for the navigation star catalog in the designated sky region.

[0026] S7. Define a three-dimensional array of navigation star catalog: NavStarTab[num][NS][Dec]: Where num represents the number of celestial regions to be divided, with the first celestial region starting from 0 and ranging from 0 to 1. -1, for example, the celestial sphere is divided into 12 regions, 6 in the north and 6 in the south, so the value of num is 0~5; the value of NS is 0~1, where 0 indicates that it is located in the northern hemisphere and 1 indicates that it is located in the southern hemisphere; the value of Dec is 0~1, where 0 indicates right ascension and 1 indicates declination.

[0027] Bind the right ascension and declination of the center points of all navigation star catalogs calculated in step S6 into the array NavStarTab[num][NS][Dec]. For example, if it is determined that the number of navigation star catalogs uniformly selected within the celestial sphere constructed in the heliocentric inertial coordinate system is 12, then calculate NavStarTab[1][0][0] for each of the northern and southern sky regions. NavStarTab[0][1][1] = (This indicates the right ascension of the second celestial region in the Northern Hemisphere) , indicating the declination of the first celestial region in the Southern Hemisphere.

[0028] The latitude and longitude results corresponding to the array are as follows: The method for constructing an on-orbit calibration navigation star catalog for optical payloads in this embodiment establishes magnitude and reference angular distance to screen candidate navigation star catalogs, ensuring the applicability of the navigation star catalogs while improving the uniformity of the distribution of navigation stars within the catalogs. For payload applications, a navigation star catalog array is generated, and stars across the entire sky are divided in a heliocentric inertial coordinate system. The screened star catalogs are bound in a three-dimensional array format, which facilitates software implementation and on-orbit application. For on-orbit calibration of satellite optical payloads, the method solves the problem of converting the navigation star catalog to the payload's pointing target, allowing for rapid acquisition of the pointing target and completion of space calibration according to the actual engineering needs of the optical payload.

[0029] In one example, the right ascension and declination ranges of each celestial region are the same size in step S2.

[0030] In another example, if the number of sky regions for which no candidate navigation star catalog is found is greater than three, the declination width of the spherical ring is increased and steps S2 to S4 are repeated. For example, the declination width is increased by 5° each time, that is, the range of the selected spherical ring is re-divided. This process is repeated until the requirements are met. This method completes the search iteration by expanding the range of sky regions to obtain a star catalog that meets the requirements.

[0031] This embodiment also provides an on-orbit calibration method for optical payloads, including the following steps: a) Generate a three-dimensional array of navigation star tables using any of the on-orbit calibration navigation star table construction methods described in the above embodiments.

[0032] b) Based on the spacecraft orbital parameters and the solar direction vector, select candidate star catalog center points from the three-dimensional array that meet the sunlight avoidance conditions. The sunlight avoidance conditions require that the angle between the sun and the pointing direction be greater than a safety threshold.

[0033] c) Calculate the angular distance between the spacecraft's current position and each candidate center point, and select the target with the smallest angular distance.

[0034] d) Control the attitude maneuver to point the optical payload toward the center point of the selected target.

[0035] This on-orbit calibration method ensures the safety of the optical payload, avoids interference from sunlight at the pointed-to star catalog location, and can locate the nearest star catalog target based on the spacecraft's position in the sky. The payload can point to the target through attitude maneuvers in the shortest possible time, and can be maneuvered to any target star catalog location that meets the payload safety requirements via commands from the ground, thus achieving the payload calibration task. Compared to traditional star-sensitive cataloging strategies that require matching and comparing imaging images with star catalogs on the ground to obtain calibration information, this application combines practical on-orbit applications, obtaining a star catalog library covering a specified sky area and generating the star catalog library as a three-dimensional array. Generating the star catalog library in array form makes it more convenient for on-orbit applications. The optical payload can point to a specific star catalog to achieve payload calibration, greatly reducing the computational load and process of ground image processing.

[0036] Preferably, during calibration, in step b, targets within ±15 degrees of the ecliptic plane are screened and excluded simultaneously. This ensures that the optical payload is kept away from the ecliptic to avoid interference from interplanetary objects (this region is the concentrated orbital plane of solar system planets, asteroids, and comets, posing a high risk of calibration contamination; in addition, the background brightness in this region is high, resulting in a high signal-to-noise ratio for stars). It also prevents stray solar light from entering the target area and ensures the reliability of star identification (stars in the Milky Way are unevenly distributed near the ecliptic plane, resulting in an abnormal stellar density).

[0037] It is worth noting that the "ecliptic plane" mentioned above refers to the reference plane formed by extending the plane of Earth's orbit around the Sun infinitely into the celestial sphere.

[0038] Optical payloads are equipped with sunshades to prevent sunlight from entering the field of view. In this embodiment, preferably, the safety threshold is the angle between the beveled edge of the sunshade and the optical axis of the optical payload (i.e., the beveled angle of the sunshade) to prevent sunlight from entering the field of view.

[0039] This invention also provides an electronic device, including a memory and a processor. The memory stores computer-readable instructions, and the processor is used to run the computer-readable instructions. When executing a computer program, it implements the on-orbit calibration navigation star table construction method or the on-orbit calibration method in any embodiment of this invention.

[0040] This invention also provides a computer-readable storage medium storing a computer program. When executed by a processor, the computer program causes the processor to perform the on-orbit calibration navigation star table construction method or the on-orbit calibration method in any embodiment of this invention.

[0041] Specifically, a system or apparatus equipped with a storage medium may be provided, on which software program code implementing the functions of any of the embodiments described above is stored, and the computer (or CPU or MPU) of the system or apparatus may read and execute the program code stored in the storage medium.

[0042] Examples of storage media used to provide program code include floppy disks, hard disks, magneto-optical disks, optical disks (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), magnetic tapes, non-volatile memory cards, and ROMs. Alternatively, program code can be downloaded from a server computer via a communication network.

[0043] Furthermore, it should be clear that not only can the program code read by the computer be executed, but also the operating system or other components operating on the computer can be instructed based on the program code to perform some or all of the actual operations, thereby realizing the function of any of the embodiments described above.

[0044] Furthermore, it is understood that the program code read from the storage medium is written to the memory set in the expansion board inserted into the computer or to the memory set in the expansion module connected to the computer. Then, based on the instructions of the program code, the CPU or other components installed on the expansion board or expansion module execute some and all of the actual operations, thereby realizing the function of any of the above embodiments.

[0045] Those skilled in the art will understand that all or part of the steps of the above method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps of the above method embodiments. The aforementioned storage medium includes various media that can store program code, such as ROM, RAM, magnetic disk, or optical disk.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that not every embodiment contains only one independent technical solution, and in the absence of conflict between solutions, the various technical features mentioned in each embodiment can be combined in any way to form other implementation methods that can be understood by those skilled in the art.

[0047] Furthermore, without departing from the scope of the present invention, modifications to the technical solutions described in the foregoing embodiments, or equivalent substitutions of some of the technical features, shall not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing an on-orbit calibration navigation satellite catalog for an optical payload, characterized in that, Includes the following steps: S1. Set the number W of navigation star catalogs used for calibration of the optical payload within the celestial sphere constructed in the heliocentric inertial coordinate system; S2. Select one spherical ring in the northern and southern hemispheres of the celestial sphere. The two spherical rings are symmetrical along the equator. Divide the two spherical rings into W / 2 celestial regions according to right ascension. Number each celestial region and store the navigation stars in these celestial regions into the first candidate navigation star library according to the partition. S3. The navigation stars in the first candidate navigation star library are screened again in terms of brightness and stability. Navigation stars that do not meet the requirements are removed, and navigation stars that meet the brightness and stability requirements are stored in the second navigation star library. S4. Calculate the angular distance between each navigation star in the second navigation star library and set a reference angular distance. Set the number of target navigation stars M in the sky area corresponding to the field of view of the optical payload. Record the number of navigation stars whose angular distance between navigation stars is within the set reference angular distance range as n. Determine whether n>M is satisfied. If so, all navigation stars that meet the reference angular distance range will be identified as candidate navigation star catalogs, and each candidate navigation star catalog will be numbered according to the sky region it is located in and stored in the first star catalog library. Otherwise, return to the first candidate navigation satellite pool; S5. Extract the candidate navigation star catalogs in the first star catalog library according to the divided sky regions, so that each sky region corresponds to a navigation star catalog, and store it in the second star catalog library. S6. Calculate the right ascension and declination of the center points of all navigation star catalogs in the second star catalog library, and use them as imaging targets for optical payload calibration. S7. Define a three-dimensional array of navigation star catalogs, and bind the right ascension and declination of the center points of all navigation star catalogs in the second star catalog library to the three-dimensional array of navigation star catalogs.

2. The method for constructing an on-orbit calibration navigation satellite catalog according to claim 1, characterized in that: The filtering criteria in step S3 are: the star magnitude is within the range of [level1, level2] and the star attribute is identified as a non-binary star and a non-variable star navigation star.

3. The method for constructing an on-orbit calibration navigation satellite catalog according to claim 1, characterized in that: In step S5, candidate navigation star catalogs are extracted from the first star catalog library according to the divided sky regions, with each sky region corresponding to one navigation star catalog. The extraction principle is as follows: If more than one candidate navigation star catalog is selected for the same celestial region, the catalog with the most navigation stars is selected as the final navigation star catalog for that celestial region. If only one candidate navigation star list is selected within the sky region, this list will be the navigation star list selected within this sky region. If no candidate navigation star catalog is found within a given celestial region, then the navigation star catalog of the adjacent celestial region with the smaller right ascension is selected as the navigation star catalog for that celestial region.

4. The method for constructing an on-orbit calibration navigation satellite catalog according to claim 3, characterized in that: If the number of sky regions for which no candidate navigation star catalog is found is greater than three, then increase the declination width of the spherical ring and repeat steps S2 to S4.

5. An on-orbit calibration method for an optical payload, characterized in that, Includes the following steps: a) Generate a three-dimensional array of navigation star catalogs by the method described in any one of claims 1-4; b) Based on the spacecraft orbital parameters and the solar direction vector, select candidate star catalog center points from the three-dimensional array that meet the sunlight avoidance conditions, wherein the sunlight avoidance conditions require that the angle between the sun and the pointing direction is greater than a safety threshold. c) Calculate the angular distance between the spacecraft's current position and each candidate center point, and select the target with the smallest angular distance; d) Control the attitude maneuver to point the optical payload toward the center point of the selected target.

6. The on-orbit calibration method according to claim 5, characterized in that: In step b, the screening process simultaneously excludes targets within ±15 degrees of the ecliptic plane.

7. The on-orbit calibration method according to claim 5, characterized in that: The safety threshold is the angle between the beveled edge of the optical load's shield and the optical axis of the optical load.

8. An electronic device, characterized in that, include: Memory, used to store computer-readable instructions; as well as A processor for executing the computer-readable instructions to perform the method as described in any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that, It stores a computer program, which is executed by a processor to implement the method of any one of claims 1 to 7.

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