Changes in Geoid Model Interpolation
In earlier versions of Trimble Business Center, the software applied all Trimble geoid models (.ggf files) by using global coordinate positions for interpolation, and global height values for application of the interpolated geoidal separations. Now, geoid model interpolation is determined based on the model's reference ellipsoid, which is is specified in the geoid model file, indicating whether the model is configured for a global or a local ellipsoid. As a result, heights/elevations (not horizontal positions) may be changed in projects that were created before the interpolation enhancement was implemented. When this occurs, a message is displayed alerting you to the situation.
The following geoid models are affected by this change:
- NGS GEOIDXX (set to LOCAL)
- EGM96 (set to GLOBAL)
- OSU91A (set to GLOBAL)
Most users will not see any change in their heights/elevations due to this change.
Following is a list of users who will be affected, and the action they should take. For additional help, contact Technical Support.
|
Users |
Action |
|
GEOIDXX users with non-(0,0,0) transformation (for example, CORS96) |
Elevations will change if they are computed from a GNSS observation using a geoid model. Global heights will change if a point is computed or entered with an elevation. Evaluate calibrated sites and re-calibrate if necessary. Note: Most GEOIDXX users will not see a change because the default State Plane coordinate systems use a (0,0,0) transformation. |
|
EGM96 and OSU91A users |
Delete all sub-grids created from old ggf files as these were incorrectly set to LOCAL. Replace the deleted sub-grids with new sub-grids created from the new .ggf files, which are set to GLOBAL:
|
|
Minnesota and Wisconsin County Coordinate Systems (USA) users |
Switch all jobs and projects to use the newly created geoid sub-grids for these regions:
Do not use sub-grids based off of GEOIDXX models. |
