GNSS Commander currently supports more than 1700 coordinate projection systems.
In germany the official coordinate system is the Gauss-Krueger (GK) system.
The Gauß-Krüger system is a transverse mercator projection which is very similar to the universal transverse mercator
system (UTM), but the central meridians of the Gauß–Krüger zones are only 3° apart, as opposed to 6° in UTM.
The central meridian of zone 4 for example is at 12 degrees and represents longitude values from 10.5° to 13.5°.
The greater the distance between the central meridian and the longitude of the position the higher the standard deviation!
The coordinate transformation is calculated in several steps:
- Conversion of the WGS84 satellite coordinate into geocentric system (ECEF: 'Earth-Centered, Earth-Fixed')
- Shift of the converted coordinate to the destination ellispoid (e.g.: from WGS84 to Bessel)
- Convert the cartesian coordinates (X,Y,Z) into ellipsoidal coordinates
- Projection of the ellipsoidal coordinates to the plane
- Add optional offsets for easing and northing
- Definition of the source-ellipsoid (always WGS84)
- Definition of the target-ellipsoid (e.g. "Bessel 1841" if projection is Gauß-Krüger)
- 7 parameters for the datum transformation (translation xyz, rotation xyz and scale)
- Offset values for easting and northing if the projection system is "transverse mercator"
The number for Gauß-Krüger system - zone 4 is 31468: http://spatialreference.org/ref/epsg/31468/