11. Data Processing

GPS data collected for high precision applications must be post-processed to provide millimeter to meter level precision. Typically, the post-processing involves differential processing relative to a fixed base location. For certain survey types, such as stop-and–go kinematic, it is essential to process the data while still in the field as a data quality check. This allows for a re-survey if there are problems with the data. For more robust data collection methods such as static surveys, data processing in the field is not required. For many high accuracy applications final data processing in the field is not possible. Advanced data processing methods typically require internet access to continuous station data, precise satellite orbits, and on-line data processing services. A common process is to field process data as a quick quality check, then spend more time back in the office to rigorously develop the final results.

When processing GPS data, the positions are typically referenced to a precisely defined ellipsoid, such as IRTF 98 or WGS-84. These ellipsoids are mathematical representations of the shape of the Earth, and do not reflect the constant-gravity defined geoid (mean sea-level) surface of the Earth. As a result, the ellipsoidal elevations are usually significantly different from the corresponding geoid, or sea-level elevations. If the user is ultimately interested in geoid elevations, a gravity model such as EGM96 must be applied. The user may also want to apply a coordinate transformation to other reference frames or map projections.

1. Trimble Geomatics Office summary
2. Trimble GPSurvey summary
3. Auto-GIPSY on-line data processing service
4. Bernese, GAMIT, and GIPSY data processing programs
5. NIMA EGM96 Geoid Calculator
6. NGS Reference Frame Transformation
7. NGS Benchmark Index

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