A multi-station method base station coordinate self-calibration method based on absolute distance measurement

Abstract

This invention relates to a multi-station base station coordinate self-calibration method based on absolute distance measurement, comprising: setting up a base station mutual aiming self-calibration system, including at least three base stations, with tracking mirrors installed at the light emission positions of each base station; establishing a spatial coordinate system with the zero point of a first base station; measuring the distance between the first base station and the second base station, including: rotating the corresponding tracking mirrors of the first and second base stations so that the propagation directions of the measurement light emitted from the first and second base stations coincide and are opposite; obtaining a first optical path difference between the measurement light of the first base station and the reference light of the second base station; obtaining a second optical path difference between the measurement light of the second base station and the reference light of the first base station; calculating the distance between the first base station and the second base station based on the first and second optical path differences; and so on, using the above-described method for measuring the distance between the first and second base stations to obtain the distance between each base station; and completing the base station coordinate self-calibration based on the distance between each base station.

Description

Technical Field

[0001] This invention relates to a multi-station base station coordinate self-calibration method based on absolute distance measurement, and pertains to the field of optical precision metrology. Background Technology

[0002] Every object in space possesses six degrees of freedom. By determining these six pose parameters, the object's position and orientation in space can be uniquely determined. Large-scale six-DOF localization of objects has important applications in many fields: for example, in the aerospace field, the pose measurement of spacecraft is the foundation for precise networking and docking between spacecraft; in the machining field, precise end-effector pose measurement of automated robots can improve the robot's hand-eye feedback control performance and ensure the quality of processed products; in aircraft manufacturing, shipbuilding, and other applications requiring the assembly of large components, pose measurement of components can guide the assembly process and improve assembly accuracy.

[0003] Laser multistation (LMP) is a common method for large-scale pose measurement. LMP involves using three or more base stations to track at least three target points on an object, recovering the six-degree-of-freedom (DOF) pose parameters of the target point solely through distance measurement, without requiring angle measurements. In situations where measuring the complete attitude parameters of the object is not required, LMP can also be used for three-degree-of-freedom (DOF) coordinate measurements or other multi-DOF parameter measurements. For example, when measuring three-DOF coordinates, only three or more base stations need to track and measure the distance to a single target point. In LMP, the coordinates of the base stations themselves are needed as known quantities when calculating the target pose parameters. Therefore, the base station coordinates need to be calibrated before actual measurement, and the accuracy of the parameter calibration directly affects the accuracy of the target pose measurement.

[0004] Existing technologies for base station coordinate self-calibration require a redundant measurement scheme. First, at least four base stations are fixed, and a spatial coordinate system is established using these four base stations as a reference. The three-dimensional coordinates of the four base stations contain nine unknowns. Each base station simultaneously tracks a target point in the measured space, recording the distance from each base station to the target point. Subsequently, the target point is moved to multiple different locations and sequentially measured simultaneously by at least four base stations. Thus, each measurement of the target point generates three unknowns (the three-dimensional coordinates of the measured point) and establishes four equations containing these unknowns, meaning the distance from the target point to the base station equals the measured distance. After generating sufficient redundant measurement data, a numerical optimization algorithm is used to iteratively calculate the values ​​of all unknowns during the calibration process. This method requires a large amount of measurement data, necessitates the use of a numerical optimization algorithm, and is complex and time-consuming in its self-calibration process. Furthermore, this method uses an indirect measurement method for base station coordinate calibration, resulting in low self-calibration accuracy. Summary of the Invention

[0005] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, in response to the above-mentioned problems, the object of the present invention is to provide a multi-station base station coordinate self-calibration method based on absolute distance measurement, which can achieve efficient and accurate self-calibration of base station coordinates.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a multi-station base station coordinate self-calibration method based on absolute distance measurement, comprising:

[0007] A base station mutual aiming self-calibration system is set up, which includes at least three base stations, and each base station has a tracking rotating mirror at its light emission position;

[0008] Establish a spatial coordinate system using the zero point of the first base station;

[0009] Measuring the distance between the first base station and the second base station includes: rotating the corresponding tracking mirrors of the first base station and the second base station so that the propagation directions of the measurement light emitted from the first base station and the second base station are coincident and opposite; obtaining the first optical path difference between the measurement light of the first base station and the reference light of the second base station; obtaining the second optical path difference between the measurement light of the second base station and the reference light of the first base station; and calculating the distance between the first base station and the second base station based on the first optical path difference and the second optical path difference.

[0010] Similarly, the distance between each base station is obtained by using the distance measurement method for the first and second base stations described above;

[0011] The coordinates of each base station are obtained based on the distance between each base station, and the base station coordinate self-calibration is completed.

[0012] In a preferred embodiment of the present invention, the tracking mirror includes a two-dimensional turntable and a reflector. The two axes of rotation of the two-dimensional turntable intersect at a point that is the zero point of the base station. The reflector is fixedly mounted on the two-dimensional turntable, and the mirror surface of the reflector passes through the zero point of the base station.

[0013] In a preferred embodiment of the present invention, the distance between the first base station and the second base station refers to the distance between the zero point of the first base station and the zero point of the second base station.

[0014] In a preferred embodiment of the present invention, establishing a spatial coordinate system using the zero point of the first base station includes:

[0015] A spatial rectangular coordinate system is established with the zero point of the first base station (0, 0, 0) as the origin, the axis containing the zero point of the second base station (X2, 0, 0) as the X-axis, and the plane containing the zero point of the third base station (X3, Y3, 0) as the XOY plane.

[0016] In a preferred embodiment of the present invention, the testing process for the first optical path difference and the second optical path difference includes:

[0017] The first base station is equipped with at least a first collimating lens, a first beam splitter, a first detector, and a first reference lens. The second base station is equipped with at least a second collimating lens, a second beam splitter, a second detector, and a second reference lens. All base stations share a light source and an optical coupler. The first base station is equipped with a first tracking mirror at the light output point, and the second base station is equipped with a second tracking mirror at the light output point.

[0018] The pulsed light emitted by the light source reaches the first collimating mirror and the second collimating mirror via fiber optic couplers. The light exiting the first collimating mirror enters the first beam splitter and is split into measurement light and reference light. The reference light is incident on the first reference mirror and returns along the same path before passing through the first beam splitter and entering the first detector. The measurement light passes through the first tracking mirror and the second tracking mirror to reach the second beam splitter, and is reflected by the second beam splitter to enter the second detector. The optical path of the pulsed light through the second collimating mirror, the second beam splitter, and the second reference mirror is completely symmetrical with the above optical path. The first detector and the second detector each collect a pair of pulses. By measuring the time difference between the arrival of the two pulses at the corresponding detectors, the first optical path difference and the second optical path difference are obtained.

[0019] In a preferred embodiment of the present invention, the expressions for the first optical path difference and the second optical path difference are as follows:

[0020]

[0021] In the formula, D1 and D2 are the absolute ranging readings of the first and second detectors in the mutual aiming state; L F1 L F2 This refers to the optical path length from the beam splitting point of the optical coupler to the exit ports of the first and second collimating lenses, respectively; L D1 L D2 This refers to the optical path length from the exit ports of the first and second collimating lenses to the beam splitting points of the first and second beam splitters, respectively; L U1 L U2 This refers to the optical path length from the splitting point of the first beam splitter and the second beam splitter to the zero point of the first tracking mirror and the second tracking mirror, respectively; L R1 L R2 L refers to the optical path length from the splitting point of the first beam splitter and the second beam splitter to the first reference mirror and the second reference mirror, respectively. 12 It is the optical path between the zero points of the first base station and the second base station, which is the base station spacing to be calculated.

[0022] In a preferred embodiment of the present invention, the distance between the first base station and the second base station is:

[0023] L 12 =(D1+D2) / 2-(L U1 -L R1 )-(L U2 -L R2 ).

[0024] In a preferred embodiment of the present invention, the coordinates of each base station are obtained based on the distance between each base station as follows:

[0025]

[0026] Among them, L 13 L is the distance between the first base station and the third base station. 23 This refers to the distance between the second and third base stations.

[0027] In a preferred embodiment of the present invention, when the number of base stations exceeds three, after completing the self-calibration of the coordinates of the three base stations, the distances from the three base stations to other base stations are measured respectively, and the coordinates of other base stations in the current spatial coordinate system are calculated based on the spacing between each base station.

[0028] In a preferred embodiment of the present invention, when a fourth base station is provided, the coordinates of the fourth base station (X4, Y4, Z4) are:

[0029]

[0030] Among them, L 14 L 24 and L 34 This represents the distance from the fourth base station to the first through third base stations.

[0031] Because the present invention adopts the above technical solution, it has the following characteristics:

[0032] 1. This invention is the first to propose a method for calibrating the inter-station distance in multi-station pose measurement scenarios by using base stations sharing the same light source to perform inter-station mutual aiming absolute distance measurement, thereby achieving self-calibration of base station coordinates.

[0033] 2. This invention can directly measure the absolute distance between the zero points of each base station and directly determine the coordinates of each base station based on geometric relationships. It does not require redundant measurements or optimization algorithms. For a system with n base stations, only 3n-6 measurements are needed to complete the self-calibration, thus improving the efficiency of self-calibration before measurement.

[0034] 3. This invention enables the accuracy of base station spacing measurement to reach the same level as the accuracy of absolute distance measurement of the base station itself, avoiding the problem of decreased self-calibration accuracy caused by complex base station coordinate calculation algorithms.

[0035] In summary, this invention can be widely applied to the self-calibration of base station coordinates. Attached Figure Description

[0036] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0037] Figure 1 This is a schematic diagram of a three-station measurement system for self-calibration of base station mutual aiming under an embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of the mutual aiming inter-station ranging principle of base station 1 and base station 2 according to an embodiment of the present invention. Detailed Implementation

[0039] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “described” as used herein may also include the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0040] Although terms such as first, second, third, etc., may be used in this document to describe multiple elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or segment from another. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or segment discussed below may be referred to as the second element, component, region, layer, or segment without departing from the teachings of the exemplary embodiments.

[0041] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "above," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure.

[0042] The ranging methods used in laser multistation methods mainly include IFM (Interferometric Measurement) and ADM (Absolute Distance Measurement). Among them, IFM can only measure continuously moving target points, while ADM can measure the absolute distance from the base station to the target point without requiring the target to move continuously from zero point to the target position. Based on the characteristics of ADM (Absolute Distance Measurement), this invention provides a multi-station self-calibration method based on absolute distance measurement, comprising: setting up a base station mutual aiming self-calibration system, the system including at least three base stations, each base station having a tracking mirror at its light-emitting position; establishing a spatial coordinate system with the zero point of a first base station; measuring the distance between the first base station and the second base station, including: rotating the corresponding tracking mirrors of the first and second base stations so that the propagation directions of the measurement light emitted from the first and second base stations coincide and are opposite; obtaining a first optical path difference between the measurement light of the first base station and the reference light of the second base station; obtaining a second optical path difference between the measurement light of the second base station and the reference light of the first base station; calculating the distance between the first and second base stations based on the first and second optical path differences; and so on, using the above-mentioned distance measurement method for the first and second base stations to obtain the distance between each base station; obtaining the coordinates of each base station based on the distance between each base station, thus completing the base station coordinate self-calibration. Therefore, this invention uses multiple base stations from the same light source and employs mutual aiming between base stations to achieve efficient and accurate self-calibration of base station coordinates.

[0043] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0044] The multi-station base station coordinate self-calibration method provided by this invention achieves multi-base station coordinate self-calibration based on absolute distance measurement. To achieve multi-base station coordinate self-calibration, this invention provides a base station mutual aiming self-calibration system. This system includes at least three base stations, each with a tracking mirror at its light-emitting position. Each base station contains at least a collimating mirror, a beam splitter, a detector, and a reference mirror. All base stations share a single light source and an optical coupler. It should be noted that the number of base stations performing coordinate self-calibration is not limited and can be set according to actual measurement needs.

[0045] Furthermore, the tracking mirror includes a two-dimensional turntable and a reflector. The two-dimensional turntable can be automatic or manual. The two axes of the turntable intersect at a point, which is the zero point of the base station. The reflector is fixedly set on the two-dimensional turntable. The mirror surface of the reflector passes through the zero point. The measurement light emitted by the base station is incident on the zero point and reflected by the reflector onto the measurement target.

[0046] This invention uses three base stations as an example to describe in detail the process of achieving efficient and accurate self-calibration of base station coordinates through a method of mutual alignment between base stations. This is just one example, and the invention is not limited to this. In this embodiment, all base stations share the same light source. The ADM method is used to combine the measurement light from one base station sharing the same light source with the reference light from another base station. The optical path and light source within the base station can also be modified to use other forms depending on the ADM method used. The ADM method used in this embodiment is a relatively common time-of-flight ranging method based on pulsed light sources. This is just one example, and the invention is not limited to this.

[0047] Furthermore, this embodiment employs a method of measuring light backscattering to calibrate the zero-position length of the ranging base station, thereby achieving the specific process of base station coordinate self-calibration, including:

[0048] S1. Establish a spatial coordinate system

[0049] Specifically, such as Figure 1 As shown, in this embodiment, a spatial coordinate system is established with the zero point of base station 1. That is, a spatial rectangular coordinate system is established with base station zero point 1 (0, 0, 0) as the origin, the axis where base station zero point 2 (X2, 0, 0) is located as the X-axis, and the plane where base station zero point 3 (X3, Y3, 0) is located as the XOY plane.

[0050] S2. When it is necessary to calibrate the distance between base station 1 and base station 2, first rotate the corresponding tracking mirrors of base station 1 and base station 2 so that the propagation directions of the measurement light emitted by base station 1 and base station 2 coincide and are opposite. The measurement light emitted by base station 3 is not shown in the figure.

[0051] Specifically, the distance between base station 1 and base station 2 refers to the distance between the points where the measurement light emitted by base station 1 and base station 2 is reflected on the corresponding tracking mirrors (base station 1 zero point, base station 2 zero point).

[0052] S3. After the measurement light emitted by base station 1 enters base station 2, there is an optical path difference between it and the reference light inside base station 2. This optical path difference is measured by ADM through the detector inside base station 2. The optical path difference between the measurement light of base station 2 and the reference light of base station 1 can be measured in the same way.

[0053] In this embodiment, the measurement process of the optical path difference is as follows:

[0054] The pulsed light emitted from light source A travels through an optical fiber and fiber coupler B to collimating mirror 11 of base station 1 and collimating mirror 21 of base station 2. The light exiting collimating mirror 11 enters beam splitter 12 and is split into measurement light and reference light. The reference light is incident on reference mirror 13 and returns along the same path, then passes through beam splitter 12 and enters detector 14. The measurement light is reflected by tracking mirror 15 and tracking mirror 25 to beam splitter 22, and then reflected by beam splitter 22 to enter detector 24. The optical path of the pulsed light through collimating mirror 21, beam splitter 22 and reference mirror 23 is completely symmetrical as described above, so it will not be repeated. At this time, detectors 14 and 24 each collect a pair of pulses. By measuring the time difference between the arrival of the two pulses at the detector, the optical path difference between the two pulses can be obtained, and their optical path difference is expressed by formula (1).

[0055]

[0056] In the formula, D1 and D2 are the absolute ranging readings of detector 14 and detector 24 in the mutual aiming state. F1 L F2 This refers to the optical path length from the beam splitting point of optical coupler B to the exit ports of collimating lens 11 and collimating lens 21, respectively; L D1 L D2 This refers to the optical path length from collimating lens 11 and collimating lens 21 to the beam splitting points of beam splitter 12 and beam splitter 22, respectively; L U1 L U2 This refers to the zero-point optical path lengths from the beam-splitting points of beam splitters 12 and 22 to tracking mirrors 15 and 25, respectively; L R1 L R2 This refers to the optical path length from the beam splitting points of beam splitters 12 and 22 to reference mirrors 11 and 21, respectively. 12 It is the optical path between the zero points of base station 1 and base station 2, which is the distance between base stations to be calculated.

[0057] S4. The distance between base station 1 and base station 2 is calculated based on the optical path difference mentioned above.

[0058] Specifically, by adding the two equations based on equation (1) and taking the average, we can obtain the expression for the distance between the two base stations, as shown in equation (2). The first term on the right side of the equation is the average of the sum of the optical path differences measured by the two detectors, and the last two terms are the differences between the optical path from the beam splitter to the tracking mirror and the optical path from the beam splitter to the reference mirror in the two base stations, respectively. This difference is the zero-position length of each base station itself.

[0059] L 12 =(D1+D2) / 2-(L U1 -L R1 )-(L U2 -L R2 (2)

[0060] The zero-point length refers to the difference between the optical path from the beam splitter point of the beam splitter to the zero point of the tracking mirror and the optical path from the beam splitter point of the beam splitter to the reference mirror in a base station. In other words, it is the absolute ranging reading of the detector in the base station when the light from the measuring arm returns from the zero point along the original path by the tracking mirror.

[0061] Furthermore, such as Figure 2 As shown, simply rotate the tracking mirror 15 around the reflection point to be perpendicular to the measurement light from the beam splitter 12, so that the beam returns along the original path, combines with the reference light in the base station 1, and is incident on the detector 14, and the zero-position length of the base station 1 can be measured. The zero-position lengths of the other base stations can be obtained in the same way, which will not be elaborated further.

[0062] It should be noted that other methods for calibrating the zero-position length can also be used for different base station structures. The mutual aiming method base station spacing calibration scheme used in this invention is also applicable to situations where other zero-position length calibration methods are used. This is just one example, and it is not limited to this.

[0063] S5. Following the method described above, calculate the distances L between base station 1 and base station 2, between base station 1 and base station 3, and between base station 2 and base station 3, respectively. 12 L 13 and L 23 This allows us to obtain the coordinates of each base station.

[0064] Specifically, the coordinates of each base station in the current coordinate system are calculated based on the established coordinate system, as shown in formula (3):

[0065]

[0066] It should be noted that since the essence of base station coordinate self-calibration is the calibration of the absolute distance between base stations, changing the coordinate system establishment method does not affect the applicability of the mutual aiming self-calibration method proposed in this invention. The coordinate system establishment in this embodiment is only used as an example for illustration and is not intended as a limitation.

[0067] Furthermore, for cases where there are more than three base stations, after completing the self-calibration of the three base stations, the distances from these three base stations to other base stations can be measured respectively, and the coordinates of the remaining base stations in the current coordinate system can be calculated using the same method as multi-station coordinate measurement.

[0068] For example, for a new fourth base station (X4, Y4, Z4), its distances to base station 1, base station 2, and base station 3 are L, respectively. 14 L 24 and L 34 Its coordinates can be calculated using formula (4):

[0069]

[0070] In summary, this invention is a base station coordinate self-calibration method based on absolute distance measurement in a multi-station pose measurement system. Multiple absolute distance measurement base stations sharing the same light source achieve self-calibration of inter-station distances through inter-station mutual aiming, thereby achieving self-calibration of base station coordinates. This solves the problems of low accuracy and complex calibration process in traditional self-calibration schemes, and can improve the measurement efficiency and accuracy of multi-station pose measurement systems.

[0071] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In the description of this specification, the terms "a preferred embodiment," "furthermore," "specifically," "in this embodiment," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments in this specification. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0072] 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 modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do 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 multi-station base station coordinate self-calibration method based on absolute distance measurement, characterized in that... include: A base station mutual aiming self-calibration system is set up. The system includes at least three base stations. Each base station has a tracking mirror at its light-emitting position. The tracking mirror includes a two-dimensional turntable and a reflector. The two axes of the two-dimensional turntable intersect at one point, which is the zero point of the base station. The reflector is fixedly set on the two-dimensional turntable, and the mirror surface of the reflector passes through the zero point of the base station. Establish a spatial coordinate system using the zero point of the first base station; Measuring the distance between the first base station and the second base station includes: rotating the corresponding tracking mirrors of the first and second base stations so that the propagation directions of the measurement light emitted from the first and second base stations coincide and are opposite; obtaining the first optical path difference between the measurement light of the first base station and the reference light of the second base station; obtaining the second optical path difference between the measurement light of the second base station and the reference light of the first base station; and calculating the distance between the first base station and the second base station based on the first and second optical path differences. The testing process for the first and second optical path differences includes: The first base station is equipped with at least a first collimating lens, a first beam splitter, a first detector, and a first reference lens. The second base station is equipped with at least a second collimating lens, a second beam splitter, a second detector, and a second reference lens. All base stations share a light source and an optical coupler. The first base station is equipped with a first tracking mirror at the light output point, and the second base station is equipped with a second tracking mirror at the light output point. The pulsed light emitted by the light source reaches the first collimating mirror and the second collimating mirror via fiber optic couplers. The light exiting the first collimating mirror enters the first beam splitter and is split into measurement light and reference light. The reference light is incident on the first reference mirror and returns along the same path before passing through the first beam splitter and entering the first detector. The measurement light passes through the first tracking mirror and the second tracking mirror before reaching the second beam splitter, and is reflected by the second beam splitter and enters the second detector. The optical path of the pulsed light through the second collimating mirror, the second beam splitter, and the second reference mirror is completely symmetrical with the above optical path. The first detector and the second detector each collect a pair of pulses. By measuring the time difference between the arrival of the two pulses at the corresponding detectors, the first optical path difference and the second optical path difference are obtained. Similarly, the distance between each base station is obtained by using the distance measurement method for the first and second base stations described above; The coordinates of each base station are obtained based on the distance between each base station, and the base station coordinate self-calibration is completed.

2. The multi-station base station coordinate self-calibration method based on absolute distance measurement according to claim 1, characterized in that, The distance between the first base station and the second base station refers to the distance between the zero point of the first base station and the zero point of the second base station.

3. The multi-station base station coordinate self-calibration method based on absolute distance measurement according to claim 1, characterized in that, Establish a spatial coordinate system using the zero point of the first base station, including: A spatial rectangular coordinate system is established with the zero point of the first base station (0, 0, 0) as the origin, the axis containing the zero point of the second base station (X2, 0, 0) as the X-axis, and the plane containing the zero point of the third base station (X3, Y3, 0) as the XOY plane.

4. The multi-station base station coordinate self-calibration method based on absolute distance measurement according to claim 3, characterized in that, The expressions for the first optical path difference and the second optical path difference are: ； In the formula, D 1. D 2 represents the absolute ranging readings of the first and second detectors in the mutual aiming state; L F1 , L F2 This refers to the optical path length from the beam splitting point of the optical coupler to the exit ports of the first and second collimating lenses, respectively. L D1 , L D2 It refers to the optical path length from the light outlet of the first collimating lens and the second collimating lens to the beam splitting point of the first beam splitter and the second beam splitter, respectively; L U1 , L U2 This refers to the optical path length from the splitting point of the first beam splitter and the second beam splitter to the zero point of the first tracking mirror and the second tracking mirror, respectively. L R1 , L R2 This refers to the optical path length from the beam splitting points of the first and second beam splitters to the first and second reference mirrors, respectively. L 12 It is the optical path between the zero points of the first base station and the second base station, i.e., the base station spacing to be calculated.

5. The multi-station base station coordinate self-calibration method based on absolute distance measurement according to claim 4, characterized in that, The distance between the first base station and the second base station is: 。 6. The multi-station base station coordinate self-calibration method based on absolute distance measurement according to claim 5, characterized in that, The coordinates of each base station are obtained based on the distance between them: ； in, L 13 The distance between the first base station and the third base station. L 23 This refers to the distance between the second and third base stations.

7. The multi-station base station coordinate self-calibration method based on absolute distance measurement according to claim 1, characterized in that, When there are more than three base stations, after completing the self-calibration of the coordinates of the three base stations, the distances from these three base stations to other base stations are measured respectively, and the coordinates of other base stations in the current spatial coordinate system are calculated based on the distance between each base station.

8. The multi-station method base station coordinate self-calibration method based on absolute distance measurement according to claim 7, characterized in that, When a fourth base station is set up, the coordinates of the fourth base station (X4, Y4, Z4) are: ； in, L 14 , L 24 and L 34 This represents the distance from the fourth base station to the first through third base stations.

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