GRASS -- GRASS Rasters

GDAL optionally supports reading of existing GRASS raster layers (cells, and image groups), but not writing or export. The support for GRASS raster layers is determined when the library is configured, and requires libgrass to be pre-installed (see Notes below).

GRASS rasters can be selected in several ways.

The full path to the cellhd file for the cell can be specified. This is not a relative path, or at least it must contain all the path components within the database including the database root itself. The following example opens the cell "proj_tm" within the mapset "PERMANENT" of the location "proj_tm" in the grass database located at /u/data/grassdb.
eg.
```
  % gdalinfo /u/data/grassdb/proj_tm/PERMANENT/cellhd/proj_tm
```
The full path to the directory containing information about an imagery group (or the REF file within it) can be specified to refer to the whole group as a single dataset. The following examples do the same thing.
eg.
```
  % gdalinfo /usr2/data/grassdb/imagery/raw/group/testmff/REF
  % gdalinfo /usr2/data/grassdb/imagery/raw/group/testmff
```
If there is a correct .grassrc5 setup in the users home directory then cells or imagery groups may be opened just by the cell name. This only works for cells or images in the current location and mapset as defined in the .grassrc5 file.

The following features are supported by the GDAL/GRASS link.

Up to 256 entries from cell colormaps are read (0-255).
Compressed and uncompressed integer, floating point and double precision cells are all supported. Integer cells are classified with a band type of "Byte" if the 1-byte per pixel format is used, or UInt16 if the two byte per pixel format is used. Otherwise integer cells are treated as UInt32.
Georeferencing information is properly read from GRASS.
An attempt is made to translate coordinate systems, but some conversions may be flawed, in particular in handling of datums and units.

NOTES on driver variations

For GRASS 5.7 Radim Blazek has moved the driver to using the GRASS shared libraries directly instead of using libgrass. Currently (GDAL 1.2.2 and later) both version of the driver are available and can be configured using "--with-libgrass" for the libgrass variant or "--with-grass=<dir>" for the new GRASS 5.7 library based version. The GRASS 5.7 driver version is currently not supporting coordinate system access, though it is hoped that will be corrected at some point.