Vertical Offset by Grid Interpolation (BEV AT)


Data source: EPSG

Information source: Bundesamt für Eich- und Vermessungswesen (BEV).

Revision date: 2019-12-27


The relationship between EVRF2000 Austria orthometric heights and GHA heights is available through a gridded data file of offsets (sometimes called height differences). The vertical offset at a point is first interpolated within the grid of values using horizontal positions in the MGI geographic 2D CRS.

The interpolated value is then applied as an offset:
•	If the height in EVRF2000 Austria is required when a GHA height is given, add the interpolated offset to the GHA height (EVRF2000 Austria height = GHA height + interpolated offset).
•	If the GHA height is required when an EVRF2000 Austria orthometric height is given, subtract the interpolated offset from the EVRF2000 Austria height (GHA height = EVRF2000 Austria height - interpolated offset).

Care! In the EPSG Dataset, vertical offsets are additive (for the forward transformation). See EPSG Guidance Note 7-2, Implementation Notes - Offsets. The BEV Hoehengrid documentation assumes that the offset is subtracted, and descriptions and examples reflect that convention. The source and target CRSs of the EPSG transformation reflect the EPSG additive offset convention.


For a point in Austria  at 48.27091391°N, 16.29473899°E (MGI) with EVRF2000 Austria orthometic height of 558.150 metres and GHA height of 558.613 metres:

First using bi-linear interpolation of the Hoehengrid for 48.27091391°N, 16.29473899°E, the resulting offset = -0.463m.

For the transformation from GHA height to EVRF2000 Austria height, 
EVRF2000 Austria height = 558.613m + (- 0.463m) = 558.150m.

For the transformation from EVRF2000 Austria height to GHA height,
GHA height = 558.150m - (- 0.463m) = 558.613m.
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