Reference System Transformation Methods

SuperMap ImageX Pro provides various reference system transformation methods to facilitate projection between different coordinate systems. Descriptions for each method are listed below:

Transformation Method	Description
Geocentric Transalation(3-para)	Geocentric three-parameter transformation method with relatively low accuracy.
Molodensky(3-para)	Molodensky transformation method with relatively low accuracy.
Abridged Molodensky(3-para)	Simplified Molodensky transformation method with relatively low accuracy.
Position Vector(7-para)	High-accuracy position vector method requiring seven parameters for adjustment and transformation. Considered equivalent to Coordinate Frame (7-para) with European definition where counterclockwise rotation is negative.
Coordinate Frame(7-para)	High-accuracy geocentric seven-parameter method requiring seven parameters for adjustment and transformation. Considered equivalent to Position Vector(7-para) with US/Australian definition where counterclockwise rotation is positive.
Bursa-wolf(7-para)	Bursa-Wolf method with high accuracy, requiring seven parameters for adjustment and transformation.
MolodenskyBadekas(10-para)	Molodensky-Badekas spatial coordinate transformation model with ten parameters.
China_3D_7P(7-para)	3D seven-parameter transformation model suitable for nationwide and provincial ellipsoidal surface transformations above 3-degree zones. Incorporates three translation parameters, three rotation parameters, and one scale factor, while considering differences in semi-major axis and flattening between two reference ellipsoids.
China_2D_7P(7-para)	2D seven-parameter transformation model suitable for nationwide and provincial transformations between geodetic coordinate systems above 3-degree zones. Recommended for conversions between Beijing 1954, Xi'an 1980, and China Geodetic Coordinate System 2000 due to lower vertical accuracy in local datum systems.
PROJ4 Transmethod	PROJ4 projection algorithm based on third-party PROJ4 tools, supporting more projection operations for overseas users. Only supports transformations between projections with valid EPSG codes.

These transformation methods are generally categorized into two groups:

Three-Parameter Transformation
This method assumes only spatial origin translation between geodetic reference systems (Figure 1), requiring three translation parameters (ΔX, ΔY, ΔZ). Simple calculation but lower accuracy, typically used for transformations between geocentric coordinate systems.

Seven-Parameter Transformation
This advanced method considers translation, rotation, and scale differences (Figure 2). Requires three translation parameters (meters), three rotation angles (arc-seconds), and one scale factor (parts-per-million). Scale factor represents dimensional scaling between coordinate systems.


Figure 1: Three-Parameter Method	Figure 2: Seven-Parameter Method

Note:

Selection of transformation method depends on specific requirements. Transformation accuracy relies on proper parameter settings. Parameters can be obtained from official surveying institutions, data providers, or calculated through field measurements. Validation through control points in both reference systems is essential.

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