FME Form: 2024.1
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.
Singlestep 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 <yesno>] \
[MAX_ITR <max iterations for inverse convergence>] \
[CNVRG_VAL <inverse convergence threshold for completion>] \
[ERROR_VAL <inverse convergence threshold for error reporting>] \
[ACCURACY <01000>] \
[EPSG_VAR <032767>] \
[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>]
Multistep Transformation Syntax
PATH_DEF <pathName> \
[SRC_DTM <datum name>] \
[TRG_DTM <datum name>] \
[DESC_NM <descriptive name>] \
[SOURCE <source>] \
[GROUP <group>] \
[ACCURACY <01000>] \
[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 
CSMap identifier name, as described in <FME_Install_Dir>/Reproject/MyCoordSysDefs.fme 
The name of the singlestep transformation being defined.  No  
PATH_DEF 
CSMap identifier name, as described in <FME_Install_Dir>/Reproject/MyCoordSysDefs.fme 
The name of the multistep 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  Floatingpoint number  Convergence threshold: When a reversed 2D transformation is within this distance of the real answer, iteration halts.  Yes  1.0E 09 
ERROR_VAL  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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  Floatingpoint 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 1.0x1006 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>  NTv2NADCONFRGEOJPPAR ATS77GEOCON 
Grid file format.  No  
GRID_FILE <direction>  fwdinv  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  Nongrid, singlestep transformation name  Transformation to be used if no grid files cover the coordinate being transformed.  Yes  
XFORM  <Singlestep transformation name>,<fwdinv>  Path definitions require at least one singlestep transformation to be listed. Transformations are applied in the order and direction listed.  No  
ACCURACY  01000  Not used.  Yes  8 
EPSG_VAR  Integer greater than or equal to zero  Not used.  Yes  0 
MIN_LNG  Floatingpoint number  Not used.  Yes  0 
MAX_LNG  Floatingpoint number  Not used.  Yes  0 
MIN_LAT  Floatingpoint number  Not used.  Yes  0 
MAX_LAT  Floatingpoint number  Not used.  Yes  0 