You are here: FME Workbench > Coordinate Systems and FME > Custom Coordinate Systems > Adding a Custom Coordinate System

Adding a Custom Coordinate System

Use a text editor to edit the MyCoordSysDefs.fme file in your Reproject directory. This directory is located where FME was installed on your system. (It is always good practice to create a backup copy of the file before you make any changes.)

The projection and units of your source data are not predefined within FME, so, to define them, you must edit the mapping file to add the following lines:

Coordinate System Definition Lines	Additional Information
COORDINATE_SYSTEM_DEF <coordsysname> \
PROJ <projType> \	Table of projection types
UNIT <unitName> \	Table of predefined units
(DT_NAME <datumName> \| EL_NAME <ellipName>) \	Table of predefined datums and predefined ellipsoids. Note that each coordinate system definition must specify either a datum or ellipsoid.
[<parameter> <value>]+ \
[DESC_NM <descriptive_name>] \
[GROUP <group_name>] \	Tip: Defining a unique group name allows you to sort coordinate systems by the "Group" column in the Coordinate System Gallery.
[QUAD <quadrant>] \	Quadrant definition
[SOURCE <source>] \
[ZERO_X <zero_x>] \
[ZERO_Y <zero_y>] \

For example, this mapping file fragment defines a NAD83 based UTM Zone 12 coordinate system.

COORDINATE_SYSTEM_DEF UTM12N83 \

PROJ TM \

UNIT METER \

DT_NAME NAD83 \

PARM1 -111.0 \

GROUP "Custom Group" \

SCL_RED 0.9996 \

ORG_LAT 0.0 \

X_OFF 500000.0 \

Y_OFF 0.0 \

MAP_SCL 1.0 \

ZERO_X 0.001 \

ZERO_Y 0.001

Edit, save, and close the MyCoordSysDefs.fme file.

Note that you will have to restart Workbench before FME can recognize the custom coordinate system.

The custom coordinate system will appear in the columns of the Coordinate System Gallery. These columns are, in order, Name, Description, Group, Datum, Ellipsoid, Projection, and Units.

When you update to a newer version of FME, the MyCoordSysDefs.fme file will not be overwritten. (However, it is always good practice to back up any custom files.)

Parameter Descriptions

The parameters above are described in Local Coordinate Systems.
For a complete list of generic parameters that you can define, please see Generic Parameters.

Working with Mapping Files

If you are working with custom mapping files and you set coordinate system definitions, you will have to remove the definitions after they are defined in the MyCoordSysDefs.fme file – the same coordinate system cannot be defined in both places.