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91 lines
3 KiB
HTML
91 lines
3 KiB
HTML
<html>
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<head>
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<title>GRASS Raster Format</title>
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</head>
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<body bgcolor="#ffffff">
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<h1>GRASS Raster Format</h1>
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GDAL optionally supports reading of existing GRASS raster maps or
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imagery groups, but not writing or export. The support for GRASS
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raster format is determined when the library is configured, and
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requires libgrass to be pre-installed (see Notes below).
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<p>
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GRASS raster maps/imagery groups can be selected in several ways.
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<ol>
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<li> The full path to the <tt>cellhd</tt> file can be specified. This
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is not a relative path, or at least it must contain all the path
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components within the GRASS database including the database root
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itself. The following example opens the raster map "proj_tm"
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within the GRASS mapset "PERMANENT" of the GRASS location
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"proj_tm" in the GRASS database located at
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<tt>/u/data/grassdb</tt>.
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<p>
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For example:
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<pre>
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gdalinfo /u/data/grassdb/proj_tm/PERMANENT/cellhd/proj_tm
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</pre>
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<li> The full path to the directory containing information about an
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imagery group (or the REF file within it) can be specified to refer to
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the whole group as a single dataset. The following examples do the
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same thing.
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<p>
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For example:
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<pre>
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gdalinfo /usr2/data/grassdb/imagery/raw/group/testmff/REF
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gdalinfo /usr2/data/grassdb/imagery/raw/group/testmff
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</pre>
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<li> If there is a correct <tt>.grassrc5</tt> (GRASS
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5), <tt>.grassrc6</tt> (GRASS 6) <tt>.grass7/rc</tt> (GRASS 7) setup
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file in the users home directory then raster maps or imagery groups
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may be opened just by the cell name. This only works for raster maps
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or imagery groups in the current GRASS location and mapset as defined
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in the GRASS setup file.
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</ol>
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<p>
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The following features are supported by the GDAL/GRASS link.
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<ul>
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<li> Up to 256 entries from raster colormaps are read (0-255).
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<li> Compressed and uncompressed integer (CELL), floating point
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(FCELL) and double precision (DCELL) raster maps are all
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supported. Integer raster maps are classified with a band type of
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"Byte" if the 1-byte per pixel format is used, or
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"UInt16" if the two byte per pixel format is used. Otherwise
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integer raster maps are treated as "UInt32".
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<li> Georeferencing information is properly read from GRASS format.
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<li> An attempt is made to translate coordinate systems, but some
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conversions may be flawed, in particular in handling of datums and
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units.
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</ul>
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<h2>Notes on driver variations</h2>
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For GRASS 5.7 Radim Blazek has moved the driver to using the GRASS
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shared libraries directly instead of using libgrass. Currently (GDAL
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1.2.2 and later) both version of the driver are available and can be
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configured using "--with-libgrass" for the libgrass variant
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or "--with-grass=<dir>" for the new GRASS 5.7+ library
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based version. The GRASS 5.7+ driver version is currently not
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supporting coordinate system access, though it is hoped that will be
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corrected at some point.
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<h2>See Also</h2>
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<ul>
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<li> <a href="http://grass.osgeo.org">GRASS GIS home page</a>
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<li> <a href="http://home.gdal.org/projects/grass/">libgrass page</a>
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</ul>
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</body>
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</html>
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