Datum Transformations and Grid Shift Files
From Fmepedia
FME supports conversions between coordinate systems using different datums. Many datum transformations are not mathematically definable and require the use of grid of shifts. If you attempt to make a datum transformation of this kind without the appropriate grid shift file in place FME will abort the translation. In older versions of FME the translation would continue but the FME log file would alert you that the transformation was not done correctly. Installing FME from the CD will ensure that the grid shift files provided by Safe Software are installed in the correct location. The downloaded versions of FME however do not include many of the grid shift files.
If your translation is failing or producing warnings because of missing grid shift files you can install many of them using our Grid Shift File Installer available here:
- gridshift.exe (36.6 MB) (ftp://ftp.safe.com/fme/beta/gridshift.exe)
Safe Software provides grid shift files for the following datum transformations*:
- AGD66 <-> GDA94 (Australia)
- AGD84 <-> GDA94 (Australia)
- ED50 <-> ETRF89 (Spain)
- NAD27 <-> NAD83 (Canada)
- NOTE: US NAD27 <-> NAD83 gridshift files are installed with FME.
- NTF <-> RGF93 (France)
- NZGD49 <-> NZGD2K (New Zealand)
- OSGB <-> OSTN97 (Great Britain)
- OSGB <-> OSTN02 (Great Britain)
Safe is unable to provide grid shift files for the transformations listed below. In these cases is it necessary to contact the appropriate jurisdiction to obtain the required files.
- NAD27 <-> CSRS (Canadian provinces)
- NAD83 <-> CSRS (Canadian provinces)
- ATS77 <-> NAD83 (Province of New Brunswick)
- ATS77 <-> NAD27 (Province of New Brunswick)
- TOKYO <-> TOKYO GRID (Japan)
To obtain gridshift files for Canadian CSRS and ATS77 transformations, provincial contacts are available here:
Managing your Grid Shift Files
For every datum transformation requiring the use of grid shift files FME includes a configuration file for managing the use and location of the grid shift files. These files are found in the Reproject directory in the FME installation directory. For example the file Nad27ToNad83.gdc includes file paths to both the Canadian and US grid shift files for the NAD27 <-> NAD83 transformations. You are encouraged to edit these files to ensure your FME is using the correct grid shift file for your location.
- Please note that different jurisdictions and standards may require the use of specific grid shift files not necessarily provided by Safe Software. In these cases you will need to aquire the appropriate grid shift files and edit the relevant .gdc file in the FME Reproject directory to make FME aware of these files.
For more information on this topic please see the Datums (http://docs.safe.com/fme/html/Workbench/fme_workbench_help.htm#maintaining_grid_files.htm) section in our Online Help Documentation (http://docs.safe.com/fme/html/Workbench/fme_workbench_help.htm).
