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. 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 |