DESCRIPTION

r.out.ntv2 converts a pair of GRASS raster maps containing longitude and lattitude coordinate offsets into an NTv2 grid datum shift file (if this document dissapeared it might have been moved to the new PROJ.4 wiki).

NOTES

NTv2 format supports only single-precission floating point data. GRASS double-precision DCELL data need to be reduced to FCELL before export, eg. using r.mapcalc float() function.

The user should adjust the region and resolution to match the input raster maps before export, using g.region.

PROJ.4 and the software that depend on it, including GDAL, GRASS, QGIS, assume the NTv2 grid's destination coordinate system to be WGS84. The metadata values in the grid's header set with majort, minort, systemt parameters are ignored, same as the input coordinate system parameters (majorf, minorf, systemf). They are for documentation purposes only.

The CREATED and UPDATED output grid's metadata fields are set to, respectively, current date and time, in YYYYMMDD and HHMMSS format.

SEE ALSO

NTv2 format description by ESRI

AUTHOR

Maciej Sieczka

Last changed: $Date$