The commonly used coordinate systems include the 1954 Beijing Coordinate System, the 1980 Xi'an Coordinate System, the WGS 84 Geodetic Coordinate System, and the currently required 2000 National Geodetic Coordinate System, etc. The parameters for each coordinate system are listed in the table below:

From the above parameters, it can be seen that the reference ellipsoids and datums of the four coordinate systems are all different. Therefore, the coordinate values for the same point on Earth are different in different coordinate systems. When it is necessary to convert data from one coordinate system to another, the issue of rigorousness in transformation must first be clarified. That is, coordinate transformations within the same ellipsoid are rigorous, while transformations between different ellipsoids are not rigorous. For example, transforming geodetic coordinates from the 1954 Beijing Coordinate System to Gauss-Kruger plane rectangular coordinates in the same system is within the scope of the same reference spheroid, and the transformation process is rigorous. The transformation from the 1954 Beijing Coordinate System to the 2000 National Geodetic Coordinate System belongs to transformation between different ellipsoids, and there is no single set of completely invariant parameters that can be used everywhere on Earth. Therefore, it is necessary to use a transformation model to transform spatial points from one reference ellipsoid datum to another. The process of datum transformation is the process of solving for transformation parameters. Only after obtaining the transformation parameters and performing the coordinate system transformation under the same ellipsoid datum can the final data conversion be completed; otherwise, the data cannot be correctly converted.

Coordinate Transformation Technical Process

1. Preparation Work: Collect and organize the coordinate data of coincident points used for transformation, analyze and select coincident points for transformation. The number of coincident points should meet the requirements; the coincident points should be reliable and of high accuracy; and they should be uniformly distributed to cover the entire survey area.
2. Calculation of Transformation Parameters: Based on the existing coincident points and transformation requirements, determine the transformation model for parameter calculation. During calculation, there should be redundant coincident points, and the least squares method should be used as the constraint condition to calculate the transformation parameters.
3. Accuracy Analysis: Based on the transformation parameters, calculate the coordinates of coincident points in the target coordinate system, analyze the transformation residuals. Transformation residuals are the differences between the transformed coordinates and the known coordinates of coincident points. Calculate the root mean square error of coordinate residuals to evaluate the accuracy of coordinate transformation, and eliminate gross errors based on the residual tolerance (three times the root mean square error). If the transformation accuracy evaluation is not qualified, reselect coincident points for parameter calculation.
4. Coordinate Transformation: Based on the final qualified transformation parameters, calculate the coordinates of other features in the target coordinate system.

   

Notes：

Before performing coordinate transformation, users need to understand the following issues:

• How to select coincident points?
• How to choose a transformation model?

Related Topics

Reproject Dataset

Batch Reproject

Transform Coordinates