Adding a Custom Transformation

Some datasets require a transformation that is not predefined in FME. In such a case, a custom transformation may be created. Transformation definitions may occur in an FME mapping file, as well as in the <FME_Install_Dir>/Reproject/MyCoordSysDefs.fme file.

Single-step Transformation Syntax

XFORM_DEF <xformName> \

SRC_DTM <datum name> \

TRG_DTM <datum name> \

[DESC_NM <descriptive name>] \

[SOURCE <source>] \

[GROUP <group>] \

[EPSG_NBR <epsg #>] \

[INVERSE <yes|no>] \

[MAX_ITR <max iterations for inverse convergence>] \

[CNVRG_VAL <inverse convergence threshold for completion>] \

[ERROR_VAL <inverse convergence threshold for error reporting>] \

[ACCURACY <0-1000>] \

[EPSG_VAR <0-32767>] \

[MIN_LNG <longitude>] \

[MAX_LNG <longitude>] \

[MIN_LAT <latitude>] \

[MAX_LAT <latitude>] \

METHOD <transformation method> \

[DELTA_X <x translation>] \

[DELTA_Y <y translation>] \

[DELTA_Z <z translation>] \

[ROT_X <x rotation>] \

[ROT_Y <y rotation>] \

[ROT_Z <z rotation>] \

[XLATE_X <x rotation origin>] \

[XLATE_Y <y rotation origin>] \

[XLATE_Z <z rotation origin>] \

[BWSCALE <scale>] \

[GRID_FILE <format>,<direction>,<file path>]* \

[FALLBACK <xformName>]

Multi-step Transformation Syntax

PATH_DEF <pathName> \

[SRC_DTM <datum name>] \

[TRG_DTM <datum name>] \

[DESC_NM <descriptive name>] \

[SOURCE <source>] \

[GROUP <group>] \

[ACCURACY <0-1000>] \

[XFORM <xformName>,<direction>]+

Examples

Refer to file MyCoordSysDefs.fme in folder <FME_Install_Dir>/Reproject.

Transformation Definition Parameters

Name	Range	Description	Optional	Default
XFORM_DEF	CS-Map identifier name, as described in <FME_Install_Dir>/Reproject/MyCoordSysDefs.fme	The name of the single-step transformation being defined.	No
PATH_DEF	CS-Map identifier name, as described in <FME_Install_Dir>/Reproject/MyCoordSysDefs.fme	The name of the multi-step transformation being defined.	No
SRC_DTM	Name of a datum	The name of the source datum. If omitted for a Path, this transformation is never automatically selected.	XFORM: No PATH: Yes
TRG_DTM	Name of a datum	The name of the target datum. If omitted for a Path, this transformation is never automatically selected.	XFORM: No PATH: Yes
DESC_NM	String	A descriptive name for the transformation.	Yes
SOURCE	String	The individual or agency providing the transformation parameters.	Yes
GROUP	String	The group that will appear in the Geographic Transformation Gallery in FME Workbench.	Yes
EPSG_NBR	Integer greater than or equal to zero	Used for logging if greater than zero.	Yes	0
INVERSE	Yes/No	If yes, transformation can be run in reverse (TRG_DTM -> SRC_DTM)	Yes	Yes
MAX_ITR	Integer greater than or equal to zero	Maximum number of iterations that are attempted when transformation is run reversed, in 2D.	Yes	8
CNVRG_VAL	Floating-point number	Convergence threshold: When a reversed 2D transformation is within this distance of the real answer, iteration halts.	Yes	1.0E- 09
ERROR_VAL	Floating-point number larger than CNVRG_VAL	Error threshold: When a reversed 2D transformation does not meet the CNVRG_VAL threshold after MAX_ITR iterations, the result is considered acceptable as long as it is closer than ERROR_VAL.	Yes	1.0E- 06
METHOD	See Geographic Transformations	Transformation method to be applied.	No
DELTA_X	Floating-point number	The amount the intermediary geocentric X coordinate is translated. This value must be given in meters and the direction of the translation is given by the sign of the value. Only applies to some METHODs.	Yes	0
DELTA_Y	Floating-point number	The amount the intermediary geocentric Y coordinate is translated. This value must be given in meters and the direction of the translation is given by the sign of the value. Only applies to some METHODs.	Yes	0
DELTA_Z	Floating-point number	The amount the intermediary geocentric Z coordinate is translated. This value must be given in meters and the direction of the translation is given by the sign of the value. Only applies to some METHODs.	Yes	0
ROT_X	Floating-point number	The amount of rotation about the X axis which is applied to the intermediary geocentric coordinates. This value is given in seconds of arc, and the direction of the rotation is indicated by the sign of the value. Only applies to some METHODs.	Yes	0
ROT_Y	Floating-point number	The amount of rotation about the Y axis which is applied to the intermediary geocentric coordinates. This value is given in seconds of arc, and the direction of the rotation is indicated by the sign of the value. Only applies to some METHODs.	Yes	0
ROT_Z	Floating-point number	The amount of rotation about the Z axis which is applied to the intermediary geocentric coordinates. This value is given in seconds of arc, and the direction of the rotation is indicated by the sign of the value. Only applies to some METHODs.	Yes	0
XLATE_X	Floating-point number	The X component of the point (in the source Cartesian coordinate reference system) about which the rotation is performed. Only applies to some METHODs.	Yes	0
XLATE_Y	Floating-point number	The Y component of the point (in the source Cartesian coordinate reference system) about which the rotation is performed. Only applies to some METHODs.	Yes	0
XLATE_Z	Floating-point number	The Z component of the point (in the source Cartesian coordinate reference system) about which the rotation will be performed. Only applies to some METHODs.	Yes	0
BWSCALE	Floating-point number	A scale factor that is applied to the intermediary geocentric coordinates. The value is given as a value in parts per million, and is the difference of the actual scale factor and unity. For example, a value for the scale parameter of -2.5 produces an actual scale factor of 0.9999985. That is, the actual scale factor used is arrived at by multiplying the parameter value by 1.0x10-06 and adding the result (algebraically) to 1.0. Only applies to some METHODs	Yes	0
GRID_FILE	<format>,<direction>, <file path>	METHOD=GRID_INTERP requires at least one grid file; otherwise it is invalid. The first grid file that covers the coordinate being transformed is used.	Depends on the METHOD chosen
GRID_FILE <format>	NTv2|NADCON|FRGEO|JPPAR| ATS77|GEOCON	Grid file format.	No
GRID_FILE <direction>	fwd|inv	Direction grid file should be applied.	No
GRID_FILE <file_path>	Path to a grid file	Either absolute or relative to <FME_Install_Dir>/Reproject	No
FALLBACK	Non-grid, single-step transformation name	Transformation to be used if no grid files cover the coordinate being transformed.	Yes
XFORM	<Single-step transformation name>,<fwd|inv>	Path definitions require at least one single-step transformation to be listed. Transformations are applied in the order and direction listed.	No
ACCURACY	0-1000	Not used.	Yes	8
EPSG_VAR	Integer greater than or equal to zero	Not used.	Yes	0
MIN_LNG	Floating-point number	Not used.	Yes	0
MAX_LNG	Floating-point number	Not used.	Yes	0
MIN_LAT	Floating-point number	Not used.	Yes	0
MAX_LAT	Floating-point number	Not used.	Yes	0