A method to quickly obtain CGCS2000 coordinates with an accuracy better than 5 cm

Abstract

The invention discloses a method for quickly obtaining CGCS2000 coordinates with an accuracy better than 5 cm, and specifically relates to the field of geodetic measurement technology. The invention provides a method for calculating the average value, obtains the coordinates of the national "Land State Network" stations under the ITRF2008 framework from 1998 to 2014, then uses a time series analysis method to obtain the base station speed, and finally uses a cubic spline fitting method to detect and eliminate the gross errors. The coordinate method adopts the ITRF2008 plate motion model using the rotation vector of the Eurasian plate, and the velocity field data generated by the calculation is the absolute velocity, and has been converted to the ITRF2014 reference frame. Therefore, the coordinate method deeply studies the ITRF coordinate conversion theory and method, and can quickly obtain the CGCS2000 coordinates. The research results show that the difference between the coordinate frames is very small, and the different epochs are the main reason for the coordinate difference. The velocity grid method proposed by the coordinate method is used for coordinate conversion, and the accuracy can reach the cm level, which can be widely used in engineering.

Description

Technical Field

[0001] The present invention relates to the field of geodetic measurement technology, and more specifically, to a method for rapidly obtaining CGCS2000 coordinates with an accuracy better than 5 cm. Background Art

[0002] The International Terrestrial Reference Frame is constructed from a series of ground stations with 3D Cartesian coordinates. ITRF is a reference frame (coordinate system) that specifically implements the International Terrestrial Reference Frame. Since the birth of the ITRF coordinate system, several different frames have been released (ITRF89, ITRF90, ITRF91, ITRF92, ITRF93, ITRF94, ITRF96, ITRF97, ITRF2000, ITRF2005, ITRF2008, ITRF2014).

[0003] my country has been promoting the use of the 2000 National Geodetic Coordinate System (CGCS2000) since 2008. This is a geocentric three-dimensional coordinate system based on the ITRF97 framework 2000.0 epoch. With the completion of the Beidou satellite navigation and positioning system network, the CGCS2000 coordinate system has also begun to explore the establishment of a global coordinate system.

[0004] Using the ITRF framework as a link, strict conversion can be performed between different coordinate systems. At present, the most widely used and influential version is ITRF2008. In actual work, conversion between different coordinate frames is often encountered in baseline solution or network adjustment, and even coordinate comparison and conversion under different epochs. As a result, the existing coordinate methods are often difficult to meet the rigor required for actual use, and their scope of application is greatly limited. Summary of the invention

[0005] In order to overcome the above-mentioned defects of the prior art, the present invention provides a CGCS2000 coordinate method with a precision better than 5 cm. The technical problem to be solved by the present invention is: using the ITRF framework as a link, strict conversion can be performed between different coordinate systems. In actual work, conversion between different coordinate frames, even coordinate comparison and conversion under different epochs, is often encountered in baseline solution or network adjustment, resulting in the existing coordinate method often being difficult to meet the rigor required for actual use, and the scope of its application is greatly limited.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for quickly obtaining CGCS2000 coordinates with an accuracy better than 5 cm, comprising the following steps:

[0007] S1. Under the same epoch, the conversion between different ITRF frames has a strict mathematical formula, which follows the seven-parameter conversion model between three-dimensional spatial coordinate systems, namely: three translation parameters (Tx, Ty, Tz), three rotation parameters (Rx, Ry, Rz) and scaling parameter D.

[0008] S2. At epoch t, ​​the three-dimensional space rectangular coordinate frame conversion formula is as follows:

[0009]

[0010] Among them, X, Y, Z represent the coordinates in the source ITRF frame, and XS, YS, ZS represent the coordinates in the target frame.

[0011] At any epoch t, ​​the conversion parameter acquisition formula is as follows:

[0012]

[0013] Among them, EPOCH represents the reference epoch of the framework conversion parameters, for example, the reference epoch for ITRF2008 conversion to other frameworks is 2000.00. They represent the conversion parameter and parameter rate at epoch t respectively.

[0014] S3. The coordinate values ​​of four IGS core stations in different regions of my country were tested under ITRF2014, 2020 epoch and converted to ITRF2008, 2020 epoch. It was found that the coordinate deviations of different frames in the same epoch were very small.

[0015] S4. Epoch conversion

[0016] In the same coordinate frame, the coordinates of different epochs are quite different, which is caused by the movement of crustal plates. The velocity field is a mathematical modeling of the movement of plates in a specific area. The velocity field is an important basic data for coordinate reference frame maintenance, coordinate conversion and even crustal dynamics and seismological research. It is strictly confidential data.

[0017] The measurement of the earth's surface is not fixed, but moves slowly with the tectonic movement of the earth's plates, generally on the order of cm / yr. The high-precision coordinate frame is realized and maintained by a series of point coordinates and velocities fixed to the surface (the latest ITRF14 also adds post-seismic deformation PSD). In addition to the above-mentioned frame conversion, the coordinate system conversion must also consider the influence of the velocity field.

[0018] In the same frame (Earth-centered Earth-fixed coordinate system), the coordinates of a point at different times t1 and t2 are Xt1, Yt1, Zt1 and Xt2, Yt2, Zt2 respectively, and the velocity of the point is Vx, Vy, Vz. The coordinate conversion formula at two times in the same frame is as follows:

[0019]

[0020] Wherein, the site velocity values ​​(or block motion model) Vx, Vy, Vz are difficult to measure and require continuous observation for several years. In order to obtain the site velocity, a large number of research papers have been conducted in-depth research. Commonly used methods include: global Euler vector method, local Euler vector method, grid average method and block Euler vector method. Among them, the local Euler vector method and global Euler vector method have the highest and lowest velocity value accuracy. The grid average method is used for the following reasons: 1) The grid method is second only to the local Euler vector method in terms of velocity accuracy; 2) The grid average method is very fast and easy to operate.

[0021] Speed ​​conversion formula between different frames: Vs = V + T' + (D' + R') · X

[0022] Where Vs represents the speed in the target frame, V represents the speed in the original frame, and T', D', and R' represent the speeds of translation, scaling, and rotation parameters, respectively.

[0023] The conversion from 2020.00 epoch to 2016.00 epoch under ITRF2014 is as follows:

[0024]

[0025] S5. The Chinese land drawn by GMT is divided into 137 plane velocity grids of 3°×3°. The plane velocity needs to convert the three-dimensional velocity field XYZ into ENU, and then make a velocity field file according to "longitude, latitude, easting component, northing component, error ellipse semi-major axis, error ellipse semi-minor axis, and the angle of the major axis of the ellipse rotated counterclockwise relative to the horizontal direction";

[0026] By converting the ITRF2014 frame from epoch 2020.00 to epoch 2016.00 and comparing the three-component coordinate deviations, it can be found that the accuracy is within 1 cm;

[0027] S6. Arbitrary coordinate transformation

[0028] Operation process: Convert the A frame to ITRF97 or ITRF2014, then use the grid velocity model to quickly obtain the velocity value for epoch conversion, and finally convert it to the B frame.

[0029] S7. In actual engineering projects, it is often necessary to obtain the CGCS2000 coordinates of the survey area. When no known national control points are found around the survey area, GNSS static observation for 2 hours can be used, and the IGS station data can be combined to obtain the ITRF2014 frame 2021 epoch coordinates of the survey point. The coordinates are then converted to the ITRF97 frame 2000.00 epoch to obtain the CGCS2000 coordinate system.

[0030] The reliability of the test method was tested by collecting national B-level control points, and the coordinates were calculated and converted according to the research method. The results showed that the method had high accuracy and could achieve cm-level accuracy.

[0031] ITRF2014 coordinates are converted to CGCS2000 coordinates, as shown in the following table:

[0032]

[0033] As a further solution of the present invention: the seven conversion parameters are provided by the ITRF official website. It should be noted that each conversion parameter provided by the official website has a reference epoch and rate.

[0034] As a further solution of the present invention: It is worth noting in S4 that the site speed also has a reference frame, and there may be scaling and rotation between different frames, confusing the frame problem of speed, and the worst impact of the closure error on the coordinate transformation result can reach centimeter level.

[0035] The beneficial effects of the present invention are:

[0036] The present invention obtains the base station velocity by using the time series analysis method, and finally uses the cubic spline fitting method to detect and eliminate the gross errors. The coordinate method adopts the ITRF2008 plate motion model using the rotation vector of the Eurasian plate. The velocity field data generated by the calculation is the absolute velocity and has been converted to the ITRF2014 reference frame. Therefore, the coordinate method deeply studies the ITRF coordinate transformation theory and method, and can quickly obtain the CGCS2000 coordinates. The research results show that the difference between the coordinate frames is very small, and the different epochs are the main reason for the coordinate difference. The velocity grid method proposed by the coordinate method is used for coordinate transformation, and the accuracy can reach cm level, which can be widely used in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the conversion of the three-dimensional rectangular coordinate frame of the present invention;

[0038] Figure 2 It is a schematic diagram of the arbitrary coordinate conversion operation flow of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] like Figure 1-2 As shown, the present invention provides a method for quickly obtaining CGCS2000 coordinates with an accuracy better than 5 cm, comprising the following steps:

[0041] S1. Under the same epoch, the conversion between different ITRF frames has a strict mathematical formula, which follows the seven-parameter conversion model between three-dimensional spatial coordinate systems, namely: three translation parameters (Tx, Ty, Tz), three rotation parameters (Rx, Ry, Rz) and scaling parameter D.

[0042] S2. At epoch t, ​​the three-dimensional space rectangular coordinate frame conversion formula is as follows:

[0043]

[0044] Among them, X, Y, Z represent the coordinates in the source ITRF frame, and XS, YS, ZS represent the coordinates in the target frame.

[0045] At any epoch t, ​​the conversion parameter acquisition formula is as follows:

[0046]

[0047] Among them, EPOCH represents the reference epoch of the framework conversion parameters, for example, the reference epoch for ITRF2008 conversion to other frameworks is 2000.00. They represent the conversion parameter and parameter rate at epoch t respectively.

[0048] S3. The coordinate values ​​of four IGS core stations in different regions of my country were tested under ITRF2014, 2020 epoch and converted to ITRF2008, 2020 epoch. It was found that the coordinate deviations of different frames in the same epoch were very small.

[0049] The conversion between ITRF2008 and ITRF2014 is as follows:

[0050]

[0051] S4. Epoch conversion

[0052] In the same coordinate frame, the coordinates of different epochs vary greatly, which is caused by the movement of crustal plates. The velocity field is a mathematical modeling of the movement of plates in a specific area. The velocity field is an important basic data for coordinate reference frame maintenance, coordinate transformation, and even crustal dynamics and seismological research. It is strictly confidential data.

[0053] The measurement of the earth's surface is not fixed, but moves slowly with the tectonic movement of the earth's plates, generally on the order of cm / yr. The high-precision coordinate frame is realized and maintained by a series of point coordinates and velocities fixed to the surface (the latest ITRF14 also adds post-seismic deformation PSD). In addition to the above-mentioned frame conversion, the coordinate system conversion must also consider the influence of the velocity field.

[0054] In the same frame (Earth-centered Earth-fixed coordinate system), the coordinates of a point at different times t1 and t2 are Xt1, Yt1, Zt1 and Xt2, Yt2, Zt2 respectively, and the velocity of the point is Vx, Vy, Vz. The coordinate conversion formula at two times in the same frame is as follows:

[0055]

[0056] Wherein, the site velocity values ​​(or block motion model) Vx, Vy, Vz are difficult to measure and require continuous observation for several years. In order to obtain the site velocity, a large number of research papers have been conducted in-depth research. Commonly used methods include: global Euler vector method, local Euler vector method, grid average method and block Euler vector method. Among them, the local Euler vector method and global Euler vector method have the highest and lowest velocity value accuracy. The grid average method is used for the following reasons: 1) The grid method is second only to the local Euler vector method in terms of velocity accuracy; 2) The grid average method is very fast and easy to operate.

[0057] Speed ​​conversion formula between different frames: Vs = V + T' + (D' + R') · X

[0058] Where Vs represents the speed in the target frame, V represents the speed in the original frame, and T', D', and R' represent the speeds of translation, scaling, and rotation parameters, respectively.

[0059] The conversion from 2020.00 epoch to 2016.00 epoch under ITRF2014 is as follows:

[0060]

[0061] S5. The Chinese land drawn by GMT is divided into 137 plane velocity grids of 3°×3°. The plane velocity needs to convert the three-dimensional velocity field XYZ into ENU, and then make a velocity field file according to "longitude, latitude, easting component, northing component, error ellipse semi-major axis, error ellipse semi-minor axis, and the angle of the major axis of the ellipse rotated counterclockwise relative to the horizontal direction";

[0062] By converting the ITRF2014 frame from epoch 2020.00 to epoch 2016.00 and comparing the three-component coordinate deviations, it can be found that the accuracy is within 1 cm;

[0063] S6. Arbitrary coordinate transformation

[0064] Involving any conversion between different coordinates, the operation process is: the A frame is converted to ITRF97 or ITRF2014, and then the grid velocity model is used to quickly obtain the velocity value for epoch conversion, and finally converted to the B frame through the frame.

[0065] S7. In actual engineering projects, it is often necessary to obtain the CGCS2000 coordinates of the survey area. When no known national control points are found around the survey area, GNSS static observation for 2 hours can be used, and the IGS station data can be combined to obtain the ITRF2014 frame 2021 epoch coordinates of the survey point. The coordinates are then converted to the ITRF97 frame 2000.00 epoch to obtain the CGCS2000 coordinate system.

[0066] The reliability of the test method was tested by collecting national B-level control points, and the coordinates were calculated and converted according to the research method. The results showed that the method had high accuracy and could achieve cm-level accuracy.

[0067] ITRF2014 coordinates are converted to CGCS2000 coordinates, as shown in the following table:

[0068]

[0069] The seven conversion parameters are provided by the ITRF official website (https: / / itrf.ign.fr / trans_para.php). It should be noted that each official conversion parameter has a reference epoch and rate.

[0070] It is worth noting in S4 that the site speed also has a reference frame. There may be scaling and rotation between different frames, which may confuse the speed frame problem. The worst impact of the closure error on the coordinate transformation result can reach the centimeter level.

[0071] Experiment 1: Convert the four IGS stations from epoch 2020.00 in the ITRF2018 frame to epoch 2016.00 and compare the three-component coordinate deviations.

[0072]

[0073] Conclusion: The four IGS stations were converted from epoch 2020.00 in the ITRF2018 framework to epoch 2016.00. The three-component coordinate accuracy was about 1 cm.

[0074] Experiment 2: Different frames and epoch conversions;

[0075] The A coordinate frame is converted to ITRF97, then the epoch conversion is performed using the grid velocity model, and then the frame is converted to the B coordinate.

[0076] The coordinates of the ITRF2008 frame at epoch 2017.393 are converted to the ITRF97 frame at epoch 2000.00, thus obtaining the CGCS2000 coordinate system.

[0077]

[0078] Conclusion: Test results, comparison between the real CGCS2000 coordinates of national B-level GPS control points and the conversion results (<2cm).

[0079] Finally, a few points should be explained: First, in the description of this application, it should be noted that, unless otherwise specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, which may refer to mechanical connection or electrical connection, or internal communication between two components, or direct connection. "upper", "lower", "left", "right", etc. are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may change;

[0080] Secondly: In the drawings of the embodiments disclosed in the present invention, only the structures related to the embodiments disclosed in the present invention are involved, and other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of the present invention can be combined with each other;

[0081] Finally: The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for quickly obtaining CGCS2000 coordinates with an accuracy better than 5 cm, characterized in that: The following steps are involved: S1. Under the same epoch, the conversion between different ITRF frames has a strict mathematical formula, which follows the seven-parameter conversion model between three-dimensional spatial coordinate systems, namely, seven conversion parameters: three translation parameters Tx, Ty, Tz, three rotation parameters Rx, Ry, Rz and scaling parameter D; S2. At epoch t, ​​the three-dimensional space rectangular coordinate frame conversion formula is as follows: Among them, X, Y, Z represent the coordinates in the source ITRF frame, and XS, YS, ZS represent the coordinates in the target frame; At any epoch t, ​​the conversion parameter acquisition formula is as follows: Among them, EPOCH represents the reference epoch of the framework conversion parameters. The reference epoch for ITRF2008 to convert other frameworks is 2000.00; P, They represent the conversion parameter and parameter rate at epoch t respectively; S3, the coordinate values ​​of four IGS core stations in different regions of my country were tested under ITRF2014, 2020 epochs and converted to ITRF2008, 2020 epochs, and it was found that the coordinate deviations of different frames in the same epoch were very small; S4. Epoch conversion In the same coordinate frame, the coordinates of different epochs vary greatly, which is caused by the movement of crustal plates. The velocity field is a mathematical modeling of the movement of plates in a specific area; The measurement of the earth's surface is not fixed, but moves slowly with the tectonic movement of the earth's plates, generally on the order of cm / yr. The high-precision coordinate frame is realized and maintained by a series of point coordinates and velocities fixed to the surface. In addition to the above-mentioned frame conversion, the coordinate system conversion must also consider the influence of the velocity field; In the same frame, in the Earth-centered Earth-fixed coordinate system, the coordinates of a point at different times t1 and t2 are Xt1, Yt1, Zt1 and Xt2, Yt2, Zt2 respectively, and the velocity of the point is Vx, Vy, Vz. The coordinate conversion formula at two times in the same frame is as follows: In the formula, the site velocity value or block motion model Vx, Vy, Vz is difficult to measure and requires continuous observation for several years. In order to obtain the site velocity, a large number of research papers have been conducted in-depth research. The commonly used methods are: global Euler vector method, local Euler vector method, grid average method and block Euler vector method. Among them, the local Euler vector method and global Euler vector method have the highest and lowest velocity value accuracy. The grid average method is used for the following reasons: 1) The velocity accuracy obtained by the grid average method is second only to the local Euler vector method; 2) The grid average method is very fast to obtain velocity values ​​and is simple to operate; The speed conversion formula between different frames: Vs=V+T'+(D'+R')·X Where Vs represents the speed in the target frame, V represents the speed in the original frame, T', D', and R' represent the speeds of translation, scaling, and rotation parameters, respectively; S5. The Chinese land drawn by GMT is divided into 137 plane velocity grids of 3°×3°. The plane velocity needs to convert the three-dimensional velocity field XYZ into ENU, and then make a velocity field file according to "longitude, latitude, easting component, northing component, error ellipse semi-major axis, error ellipse semi-minor axis, and the angle of the major axis of the ellipse rotated counterclockwise relative to the horizontal direction"; By converting the ITRF2014 frame from epoch 2020.00 to epoch 2016.00 and comparing the three-component coordinate deviations, it can be found that the accuracy is within 1 cm; S6. Arbitrary coordinate transformation Involving any conversion between different coordinates, the operation process is: the A frame is converted to ITRF97 or ITRF2014, and then the grid velocity model is used to quickly obtain the velocity value for epoch conversion, and finally the frame is converted to the B frame; S7. In actual engineering projects, it is often necessary to obtain the CGCS2000 coordinates of the survey area. When no known national control points are found around the survey area, GNSS static observation for 2 hours can be used, and the coordinates of the survey points in the ITRF2014 frame 2021 epoch can be obtained by combining the IGS station data. The coordinates are then converted to the ITRF97 frame 2000.00 epoch to obtain the CGCS2000 coordinate system. The reliability of the test method was tested by collecting national B-level control points, and the coordinates were calculated and converted according to the research method. The results showed that the method had high accuracy and could achieve cm-level accuracy.

2. A method for quickly obtaining CGCS2000 coordinates with an accuracy better than 5 cm according to claim 1, characterized in that: The seven conversion parameters are provided by the ITRF official website. It should be noted that each official conversion parameter has a reference epoch and rate.

3. The method for quickly obtaining CGCS2000 coordinates with an accuracy better than 5 cm according to claim 1, characterized in that: It is worth noting in S4 that the site speed also has a reference frame. There may be scaling and rotation between different frames, which may confuse the speed frame problem. The worst impact of the closure error on the coordinate transformation result can reach the centimeter level.

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