Coordinate Projection

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PilaBlu
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Coordinate Projection

Beitrag von PilaBlu » 21.10.2017, 17:02

The WGS84 position can be optionally converted to a local coordinate system.
GNSS Commander currently supports more than 1700 coordinate projection systems.

In germany the official coordinate system is the Gauss-Krueger (GK) system.
:arrow: http://wiki.openstreetmap.org/wiki/DE:Gauß-Krüger

gk-system.png
gk-system.png (32.42 KiB) 411 mal betrachtet

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:
  1. Conversion of the WGS84 satellite coordinate into geocentric system (ECEF: 'Earth-Centered, Earth-Fixed')
  2. Shift of the converted coordinate to the destination ellispoid (e.g.: from WGS84 to Bessel)
  3. Convert the cartesian coordinates (X,Y,Z) into ellipsoidal coordinates
  4. Projection of the ellipsoidal coordinates to the plane
  5. Add optional offsets for easing and northing
For this calculation you need the following parameters:
  • 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"
Most of this parameter sets are available by the EPSG (European Petroleum Survey Group Geodesy) number.
The number for Gauß-Krüger system - zone 4 is 31468: http://spatialreference.org/ref/epsg/31468/

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