At present, the commonly used coordinate systems include 1954 Beijing Coordinate System, 1980 Xi'an Coordinate System, WGS 84 Geodetic Coordinate System and 2000 National Geodetic Coordinate System currently required to be used. The following table shows the Parameters of each coordinate system:
| Coordinate System | Reference ellipsoid | Major semi-axis | Flattening rate |
| Beijing Coordinate System 1954 | Krasovsky | 6378245 | 1：298.3 |
| 1980 Xi'an coordinate system | IAG-75 International Ellipsoid | 6378140 | 1：298.257 |
| WGS 84 | WGS 84 | 6378137 | 1：298.257223563 |
| National Geodetic Coordinate System 2000 | CGCS2000 | 6378137 | 1：298.257222101 |
From the above parameters, it can be seen that the reference ellipsoid matrix and datum plane of the four coordinate systems are different, so the coordinate values of the same point on the earth in different coordinate systems are different. When a piece of data needs to be transformed from one coordinate system to another coordinate system, the strictness of the transformation should be made clear first, that is, the Coordinate Transformation in the same ellipsoid is rigorous, while the transformation between different ellipsoids is not rigorous. For example, the geodetic Coordinate Transformation of the 1954 Beijing coordinate system to the Gaussian plane rectangular coordinate of the 1954 Beijing coordinate system is a Coordinate Transformation in the same Reference Spheroid category. The conversion process is rigorous. The transformation from the 1954 Beijing Coordinate System to the 2000 National Geodetic Coordinate System belongs to the transformation between different ellipsoids, and there is no set of completely unchanged parameters that can be used at all locations on the earth. Therefore, it is necessary to transform the space point from Coordinate Transformation under a reference ellipsoid datum to another reference ellipsoid datum through the transformation model. The process of datum transformation is the process of solving Transformation Parameters. After the Transformation Parameters are obtained, the coordinate system is transformed under the same ellipsoid datum to complete the final transformation of the data, otherwise the data can not be transformed correctly.
Coordinate Transformation Technical Flow
- Preparation: Collect and sort out the coordinate data of coincident points for conversion, and analyze and select the coincident points for conversion. The number of coincident points shall meet the requirements. The coincident points shall be reliable and have high precision. The coincident points shall be evenly distributed to cover the whole survey area.
- Transformation Parameters Calculation: determine the transformation model for parameter calculation according to the existing coincidence point results and transformation requirements. There shall be redundant coincident points during calculation, and the transformation parameters shall be calculated by using the least square method as the constraint condition.
- Precision Analysis: Calculate the coordinates of the coincident points of the Target Coordinate System according to the Transformation Parameters, and analyze the transformation residual error. The transformation residual error is the difference between the coordinates of the coincident points after transformation and the known coordinates. Calculate the mean square error of coordinate residuals to evaluate the accuracy of Coordinate Transformation, and eliminate gross errors according to the residual tolerance (3 times the mean square error of residuals). If the evaluation of conversion accuracy is not qualified, the coordinates of coincidence points shall be re-selected for parameter calculation.
- Coordinate Transformation: Calculate other figure coordinates of Target Coordinate System according to the final qualified Transformation Parameters.
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Related topics
Dataset Projection Transformation
Batch Projection Transformation