Geodetic Survey Division, Natural Resources Canada.
2016-12-15
true
false
false
(none)
urn:ogc:def:method:EPSG::1060
Geographic3D to GravityRelatedHeight (CGG2013)
For consistency with earlier models the Information Source references software which uses bi-quadratic interpolation. Because of denser node spacing in CGG2013 bi-linear interpolation will be sufficient for most uses. See Info Source for file format doc.
This transformation involves the application of a geoid-ellipsoid separation value interpolated from a geoid model. The model provides separation values at the nodes on a regular grid of latitude and longitude intersection points. The geodetic latitude and longitude used to interpolate within the grid are not affected by this transformation.
The grid is referenced to a specific geographic CRS (the source CRS) and interpolation must be made in this system.
Calculation of the separation is achieved through a bi-quadratic interpolation of the grid, using the latitude and longitude of the point. This step provides the geoid-ellipsoid separation (N) above the ellipsoid of the source Geographic 3D CRS.
Then:
H = h - N
where h = the height above the ellipsoid in the source geographic 3D CRS
and H = the gravity-related height in the target vertical CRS.