Explanation of the Coordinate Systems Exceptions Folder in FME Desktop

Question

What are Coordinate System Exceptions?

Answer

Definition

The exceptions folder stores mappings that are used to match FME coordinate systems to the coordinate systems of other applications.

This action is necessary because coordinate system names & definitions for the same coordinate system may vary (ever so slightly) between different applications. Therefore the only way to 100% guarantee pleasing accurate mapping between FME Coordinate Systems and Application Coordinate Systems is to maintain a lookup table that goes from FME internal names to the coordinate system representation used by the application.

Files

The exceptions files are currently these:

• autodeskwkt.db

• epsg.db

• esriwkt.db

• mapinfo.db

• oracle.db

The files can be located in <fme_install_dir>\reproject\exceptions

File Structure

The exception files are always structured so that the first match found in the file "wins". This allows several application representations to map to the same FME internal name, for example, but the first occurrence of the FME internal name would "win" when the application representation was being looked up.

Adding Exceptions

Exceptions files may occasionally be out of date, since we rely on the application creators to provide their list of supported coordinate systems and, of course, we can't account for custom coordinate systems.

In order to make modifications to the ESRI coordinate systems see the (ESRI exceptions update instructions).

For the other exceptions files, Safe recommends that users NOT add to the exceptions files themselves but instead involve Safe support.