Benefits
Gtrans is widely used for coordinate transformation within Sweden as it is officially recommended, translates between numerous local coordinate systems, and supports rubbersheeting transformations. Within FME, support for Gtrans naturally complements and extends comprehensive transformation and reprojection capabilities.
Availability
Gtrans is available within the standard FME product and also within FME Server (which means it can be used from SpatialDirect). Gtrans is available on the Windows platform only and in the 32 bit version of FME only. For licensing reasons it is not available within the ESRI Data Interoperability Extension.
If Gtrans is unavailable, the CS-MAP reprojection engine also supports Swedish coordinate systems. It is important to be aware that CS-MAP reprojects some Swedish systems using direct projection.
Available Functionality
The @Reproject command has been updated with new options, and the GtransReprojector and GtransAttributeReprojector transformers are now available in Workbench.
Installation
Gtrans is installed as part of the full FME product.
The product installs to <fme install dir>/Reproject/Gtrans
There are three subdirectories, of which Sys is the most important. It contains a whole series of transformation files.
- *.TF - transformation file
- *.TFI - Inverse transformation file
- *.TR1 and *.TR2 - Rubbersheet transformation files
Operation
Gtrans transformation is done through a transformer, and not reader/writer settings.
Vector Data
This workspace(gtrans1.zip) is an example of Gtrans reprojection of vector data.
Above: Workspace set up to read data and carry out Gtrans reprojection.
Above: Settings dialog for GtransReprojector transformer. The "translation file" setting is asking for the *.TF file to use.
Above: Clicking the button to browse for the "translation file" opens this dialog. Here is selected the TF for converting SWEREF 99 lat long to SWEREF 99 14 15.
Above: Data before in LL...
Above: ...Data after, in RT90
Raster Data
This workspace(gtrans2.zip) is an example of Gtrans reprojection of raster data.
For raster transformations the Reverse Translation File must be supplied in addition to the normal (forward) Translation File. You may also select the raster interpolation type and cell size.
Attribute Data
This workspace(gtrans3.zip) is an example of Gtrans reprojection of attribute data.
Gtrans attribute transformations work the same way as the usual AttributeReprojector transformer.
Q+A
Q) What happens when I already have a coordinate system set on the destination dataset? Will FME reproject the data a second time?
A) No. The data that exits a GtransReprojector transformer has no coordinate system tag, therefore it will not get reprojected by a writer (unless you set the coordinate system deliberately with a CoordinateSystemSetter).
Q) How does FME match its own coordinate systems with the ones in Gtrans?
A) It doesn't. There is no correlation between the two and (as yet) no lookup table that lists matches. If you are aware that your Gtrans coordinate system is an exact match for one of FME's, then you can tag your features using the CoordinateSystemSetter transformer. The main reason to do this is so that when you write the data to an output format, the output format will end up storing the correct coordinate system.