Working with Coordinate Systems in FME

FME Version

Introduction

A coordinate system is a 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.

For further information, please consider reviewing our documentation, Working with Coordinate Systems, and Reprojecting Data.

Terminology

Coordinate System: A mathematical system that describes the position of points in a space.
Datum: A reference for representing the position of locations on earth precisely by means of geodetic coordinates.
Ellipsoid Height: The difference between the ellipsoid and a point on the surface of the earth.
Projection: A mathematical way of portraying the earth on a flat surface to create a map. One component of a Coordinate System
Reprojection: A spatial term meaning to change the projection from one to another

Setting Coordinate Systems

Setting a Source Coordinate System

Most formats read by FME will have a coordinate system defined on them. However, for those that have no coordinate system defined, or have an incorrect coordinate system, FME allows you to set the source coordinate system. This setting will override the coordinate system read from the data.

Coordinate systems are defined while reading in the data, or they can be set in the Navigation window. A coordinate system can be changed by double-clicking the setting or by right-clicking and choosing the edit parameter option.

Coordinate System Gallery

You can type the name of the coordinate system directly, but if you are unsure, you can choose from the Coordinate System Gallery. The gallery can be accessed by clicking on the drop-down arrow inside of the Coordinate System box and selecting More Coordinate Systems.

Setting a Destination Coordinate System

Unlike setting the Source Coordinate System, setting the Destination Coordinate System does not override the coordinate system on the data, but forces a reprojection if it is different than the coordinate system of the data. This is referred to as Implicit Reprojection.

Implicit reprojection uses the CS-MAP reprojection engine to do a horizontal reprojection only, with the default datum transformation.

When reprojecting data using the destination coordinate system setting, the reprojection happens after any processing in the workspace is complete. If you wish to perform an operation on data with disparate coordinate systems, you will need to use one of the reprojector transformers to explicitly reproject to the same coordinate system before doing the operation.

Reprojector Transformers

Reprojection, including datum and ellipsoid transformation, is a complex mathematical operation. Different reprojection engines may produce slightly different results for the same reprojection. For this reason, FME has several reprojector transformers, using different reprojection engines:

CsmapReprojector uses the CS-MAP reprojection engine to do horizontal and vertical transformations. CS-MAP 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. CS-MAP is also used by Autodesk applications.
Reprojector is a simpler version of the CsmapReprojector for horizontal reprojection only. It does not allow you to choose a datum transformation, or override the source data coordinate system.
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.
GridInQuestIIReprojector uses the GridInQuest reprojection engine to perform horizontal and vertical transformations within the United Kingdom and Ireland.
GTransReprojector uses the GTrans reprojection engine to perform coordinate system conversion in the Scandinavian region.
ReframeReprojector uses the Reframe Library from the Federal Office of Topography (swisstopo) and it is used to reproject feature coordinates within Switzerland.
PROJReprojector uses the PROJ library to reproject feature coordinates from one coordinate system to another.

Those new to reprojection will find the Reprojector the easiest to use, while those more familiar may prefer the increased capabilities of the CsmapReprojector.

Examining a Dataset’s Coordinate System

If your data has a coordinate system defined, it will display in the FME Data Inspector, in the Feature Information pane:

Generally, the displayed coordinate system’s name will match a defined CS-MAP coordinate system, but there are a few exceptions:

Esri Shape and Geodatabase dataset coordinate system names will be prefaced with an underscore. This is done so that the Esri coordinate system WKT read from the source can be included in the coordinate system definition, ensuring that an Esri -> Esri conversion will retain the exact coordinate system definition.
_FME_0, _FME_1, etc. are used when the coordinate system on the source data does not match any of the CS-MAP coordinate systems. In this case, FME creates a temporary coordinate system for use within the conversion.
KML_COORDSYS_0, SKP_COORDSYS_0 are used for 3D models stored in Google Earth and Sketchup datasets. These models are stored in a local coordinate system referenced to a latitude and longitude. FME creates a custom local coordinate system from the lat/long, allowing these datasets to be reprojected into standard coordinate systems.

If you click on the coordinate system, a dialog will pop up displaying the coordinate system parameters:

This is helpful in comparing CS-MAP coordinate systems to those on other applications.

Custom Coordinate Systems

FME comes with around 5600 pre-defined coordinate systems, but occasionally it may be necessary to add a new coordinate system. The procedure for doing so is described in the FME documentation at Adding a New Coordinate System, but we have recently added a web interface to allow you to create a new definition interactively, at Define Custom Coordinate Systems.

Vertical Coordinate Systems

FME is able to reproject vertical coordinate systems. For more information, see Which transformer do I use to do 3D reprojection (vertical datums)?

Articles

Documentation

How FME Identifies Coordinate Systems
Reprojecting Data
Custom Coordinate Systems
Adding a Custom Transformation
Shared Directories
Included Grid Shift Files
Adding Grid Files
Using the CoordinateSystemSetter Transformer
Coordinate Systems Files Reference

Additional Resources

Blogs

3 Key Concepts in Coordinates and Mapping
4 Options for Mapping our (Locally) Flat World
Axis Order in Spatial Data
Coordinate Systems 101: The Basics
Coordinate Systems and Earth Movements
Datums in GIS: Coping With the Limits of Lat/Long
Handling the Unknown Coordinate System
Heights in Coordinate Systems
Moving to Standardization in Coordinate Reprojection: CS-MAP, Datum Shifts, and Axis Order
Orientation and Geodetic Data
The Difference Between Geocoding & Georeferencing

Presentations

X and Y Mark the Spot, but on What Map? Dealing With Custom Coordinate Systems in FME [16:06]

Webinars

Coordinate Systems in FME 101 [47:25]

Troubleshooting

Cannot Reproject NAD27 - NAD83 on FME Server
Dateline Problem
GDAL/PROJ Library Updates Affect Coordinate System Handling
Missing Coordinate System
Resolving an unrecognized Esri Coordinate System Exception

Known Issues

For a list of Known Issues, see the following articles: 2021.x, 2020.x, 2019.x, 2018.x, 2017.x

FME Fails to Write Coordinate System to Autodesk Map 3D Dataset

Support

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