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Datum Definition

Certain sites may require a datum that is not predefined in FME. In such a case, a custom datum may be created. Datum definitions may occur in an FME mapping file, as well as in the LocalCoordSysDefs.fme file (<FME_Install_Dir>/Reproject/LocalCoordSysDefs.fme). The syntax of a datum definition is:

DATUM_DEF <datumName> \

DESC_NM <descriptive name> \

SOURCE <source> \

ELLIPSOID <ellipsoid name> \

USE <use type> \

DELTA_X <x value> \

DELTA_Y <y value> \

DELTA_Z <z value> \

BWSCALE <bwscale> \

ROT_X <rotX> \

ROT_Y <rotY> \

ROT_z <rotz>

Example datum definition

This mapping file fragment defines a datum with the BURSA use-type:

DATUM_DEF DHDN \
   DESC_NM “Deutsches Hauptdreicknetz (DHDN)” \
   SOURCE “German Government” \
   ELLIPSOID BESSEL \
   USE BURSA \
   DELTA_X 582.00000000000 \
   DELTA_Y 105.00000000000 \
   DELTA_Z 414.00000000000 \
   BWSCALE 8.3000000000000
   ROT_X -1.0400000000000
   ROT_Y -0.35000000000000
   ROT_Z 3.0800000000000

For additional examples, see <FME_Install_Dir>/Reproject/LocalCoordSysDefs.fme. Note that at least one transformation should be added for most datums. For more information, see Adding a Custom Transformation.

Datum Definition Parameters

Name

Range

Description

Optional

DATUM_DEF

CS-Map identifier name, as described in <FME_Install_Dir>/Reproject/LocalCoordSysDefs.fme

The name of the datum being defined.

No

DESC_NM

any string

A descriptive name for the datum.

Yes

SOURCE any string The individual or agency providing the datum parameters. Yes
ELLIPSOID valid ellipsoid The ellipsoid upon which the datum is based.

No

USE See Datum USE Methods

The type of approximation used when the datum is involved in a datum conversion. Not used in FME 2013 or later workspaces.

Yes

DELTA_X

floating point value

The X component of the vector from the geocenter of the datum being defined to the geocenter of the WGS-84 datum.
Not used in FME 2013 or later workspaces.

Units: meters.

Yes

DELTA_Y floating point value

The Y component of the vector from the geocenter of the datum being defined to the geocentre of the WGS-84 datum. Not used in FME 2013 or later workspaces.

Units: meters.

Yes

DELTA_Z floating point value

The Z component of the vector from the geocenter of the datum being defined to the geocenter of the WGS-84 datum. Not used in FME 2013 or later workspaces.

Units: meters.

Yes

BWSCALE floating point value

The scale factor employed by the BURSA use-type, in parts per million. Not used in FME 2013 or later workspaces.

Yes

ROT_X floating point value

The X rotation factor employed by the BURSA use-type. Not used in FME 2013 or later workspaces.

Units: Seconds of arc.

Yes

ROT_Y floating point value

The Y rotation factor employed by the BURSA use-type. Not used in FME 2013 or later workspaces.

Units: Seconds of arc.

Yes

ROT_Z floating point value

The Z rotation factor employed by the BURSA use-type. Not used in FME 2013 or later workspaces.

Units: Seconds of arc.

Yes