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Satellite Vectors

Gemini Terrain can process data measured with satellite equipment. This can be data collected in real-time or static measurements that have been post-processed. For differential measurements, a spatial vector is calculated that can be expressed by dX, dY, and dZ components in a 3D geocentric coordinate system. This vector contains information that can be transformed to distance, direction angle, and height difference between the observed points. After transformation, the observations are in the same form as conventional observations. You can therefore perform an adjustment based solely on satellite data or together with conventional data.

Procedure for Processing Satellite Vectors

The procedure for processing satellite vectors can be summarized in the following main points:

Procedure

  1. Import vector data
  2. Transform vector to distance, direction angle, and height difference
  3. Adjustment calculation

Import of Vector Data

When importing satellite data, it is the vectors with associated standard deviations and correlations that are imported. See Import from Field Book. You currently have the option to import vector data in the following formats:

  • KOF format (among others, Javad uses this format)
  • Trimble DC77
  • Trimble TGO
  • Leica ascii
  • Ashteck binary format
  • Geolab ascii
  • NGS Bluebook
  • Magellan

Transformation

As the vectors are imported into the project, an automatic transformation to direction angle, zenith distance, and horizontal distance occurs. For more information about when and how a transformation is performed, see Vector Transformation.

Important Information About Coordinate System

It is important that the correct coordinate system is selected for the project. This is crucial for the transformation to produce correct values as a basis for the adjustment.

Adjustment Calculation

Before performing the adjustment calculation, you should check whether the standard deviation for the observations has realistic values. Often, satellite receivers themselves can deliver standard deviations that are overly optimistic. If they are not realistic, you should recalculate the standard deviations based on instrument parameters. This is done from the Satellite Vectors list. Select all observations, right-click, and choose Calculate Standard Deviation from Instr. If you want to get the original data back, simply run a new transformation. Select all observations, right-click, and choose Transform Satellite Vector w/ Standard Deviation.

Since the satellite vectors are transformed to direction angle, zenith distance, and horizontal distance, the final calculation is performed in the same way as for conventional observations. See Adjustment Calculation.

Important Information

It is only during the adjustment calculation that the observations are corrected for map projection, plumb line deviation, and earth curvature.