The geocoordination system now contains a way to override any datum definition by adding uncommented entries in a user override file.
Delivered with MicroStation CONNECT in the MicroStation\GeoCoordinateData folder is a file called UserOverrideGeodeticTransformSeed.asc. This file contains entries for all geodetic transformations that currently make use of grid shift files.
To add a new grid shift override file, create an empty text file in the coordinate system dictionary folder. (Usually MicroStation\GeoCoordinateData). This file must be called UserOverrideGeodeticTransform.asc
From UserOverrideGeodeticTransformSeed.asc locate the section pertaining to the geodetic transformation to be overridden. Copy this section and paste it into the newly created empty file.
Uncomment the section in the new file by removing the ‘#’ symbol from the front of each line.
Add an entry introducing the new grid shift file. An example for the ED50-IGN.ES datum is below. Here we are adding an entry for a new grid file called NEW_USER_FILE.gsb.
More details are described in the comment section of UserOverrideGeodeticTransformSeed.asc.
GX_NAME: ED50-IGN.ES_to_ETRF89 SRC_DTM: ED50-IGN.ES TRG_DTM: ETRF89 DESC_NM: ED50 to ETRF89 via Grid File (Canadian NTv2 format) SOURCE: Instituto Geográfico Nacional, Spain EPSG_NBR: 0 INVERSE: Yes MAX_ITR: 10 CNVRG_VAL: 1e-09 ERROR_VAL: 5e-08 ACCURACY: 1.0 METHOD: GRID_INTERP GRID_FILE: NTv2,Fwd,.\Spain\sped2et-2005.gsb GRID_FILE: NTv2,Fwd,.\Spain\BALR2009.gsb GRID_FILE: NTv2,Fwd,.\Spain\R2009V9.gsb GRID_FILE: NTv2,Fwd,.\Spain\NEW_USER_FILE.gsb FALLBACK: ERP50-SP-EST99_to_WGS84
If the override file is a well-known addition to your geocoordination workflow, then please contact Bentley through the normal support channels to have it added to the product in a later release.