Description

A coordinate system is mathematical model of the conversion between the data coordinates and a specific location on the Earth.

In order to be truly georeferenced, data needs to have a coordinate system associated to it. FME will gladly handle data without any coordinate system, but without a defined coordinate system, it will not be possible to accurately combine the dataset with those in other coordinate systems.

Coordinate system definitions are specified by a set of parameters that define this mathematical model, including the earth model (ellipsoid or datum), the units used to measure the coordinates, the projection type, and any parameters specific to the projection type

Setting a Coordinate System

Coordinate systems are defined in the navigation pane of Workbench. A coordinate system can be changed by double-clicking the setting or by right-clicking and choosing the edit parameter option:

Implicit Reprojection

Setting the source coordinate system will override any coordinate system read from the dataset. Setting the destination coordinate system will force a reprojection of any data sent to the writer that is not in that coordinate system.

Here the user is reprojecting data from a Lat-Long coordinate system to a UTM zone:



When reprojecting data using the destination coordinate system setiing, the reprojection happens after any processing in the workspace is complete. If you wish to perfom an operation on data with disparate coordinate systems, you will need use the Reprojector transformer to explicitly reproject to the same coordinate system before doing the operation.

 

Reprojection Engines

FME's implicit reprojection uses the CS-MAP reprojection engine, as does the Reprojector transformer. This is a general reprojection engine that is included with FME and includes definitions for thousands of coordinate systems, with a large variety of projections, datums, ellipsoids and units. The user can easily define their own coordinate systems and datums by adding the definition to the file FME\Reproject\MyCoordSysDefs.fme. For more details on defining new coordinate systems and datums, please see the FME Coordinate System documentation.

FME also has specialized reprojection transformers for other reprojection engines:

• CsmapReprojector uses the same CS-MAP engine as the Reprojector, but also performs vertical transformations.
• ESRIReprojector uses the ArcGIS reprojection engine. ArcGIS must be installed and licensed on the same computer as FME for this transformer to work. It uses the ArcGIS reprojection interface to choose both the coordinate systems and datum transformations, and supports user created coordinate systems and datums transformations.
• GridInQuestReprojector uses the GridInQuest reprojection engine to perform horizontal and vertical transformations within the United Kindom and Ireland.
• GTransReprojector uses the GTrans reprojection engine to perform coordinate system conversion in the Scandinavian region.

FME includes a Software Development Kit to allow third parties to develop their own reprojection engines, so this list  will grow in the future. We anticipate adding the BlueMarbleReprojector in the spring of 2012.