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. 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>
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 |
\ \ \ \ \ \ \ \ |
|
Name |
Range |
Description |
Optional |
|
<datumName> |
any string |
The name of the datum being defined. |
No |
|
<descriptive name> |
any string |
A descriptive name for the datum. |
Yes |
|
<source> |
any string |
The individual or agency providing the datum parameters. |
Yes |
|
<ellipsoid name> |
valid ellipsoid |
The ellipsoid upon which the datum is based. |
No |
|
<use type> |
3PARAMETER 4PARAMETER 6PARAMETER 7PARAMETER AGD66 AGD84 ATS77 BURSA CSRS DHDN GDA94 HPGN JGD2K MOLODENSKY MULREG NAD27 NAD83 NZGD2K NZGD49 WGS72 WGS84 |
The type of approximation used when the datum is involved in a datum conversion. |
No |
|
<x value> |
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. |
No |
|
<y value> |
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. Units: meters.
|
No |
|
<z value> |
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. Units: meters. |
No |
|
<bwscale> |
floating point value |
The scale factor employed by the BURSA use-type, in parts per million. |
Not used by all datum types. |
|
<rotX> |
floating point value |
The X rotation factor employed by the BURSA use-type. Units: Seconds of arc. |
Not used by all datum types. |
|
<rotY> |
floating point value |
The Y rotation factor employed by the BURSA use-type. Units: Seconds of arc. |
Not used by all datum types. |
|
<rotZ> |
floating point value |
The Z rotation factor employed by the BURSA use-type. Units: Seconds of arc. |
Not used by all datum types. |