[Mapserver-users] Non-8bit Raster Classification and NODATA

[Frank Warmerdam]

Folks,

I have committed support for proper classification of non-8bit rasters in
MapServer.  I hope to update the mapfile reference, and raster howto about
this soon, but the basics that non-8bit rasters are now supported for
a more refined classification (via a 16bit lookup table).  Some notes:

  o Only works via GDAL raster module.
  o Only [pixel] can be used in expressions on these rasters, [red], [green]
    and [blue] will be ignored.
  o Internally mapserver is preparing a lookup table with up to 65536 entries
    (buckets) so you still don't get complete accurancy when classifying floating
    point values.
  o For any 16bit integer rasters (signed or unsigned) classification results
    should be exact.
  o For floating point rasters scaling to the 16bit lookup table may be explicitly
    controlled via the SCALE and SCALE_BUCKETS PROCESSING options.  By default
    scale min and max are computed from the data, and 65536 buckets are used.
  o I have added support for a NODATA PROCESSING keyword so that non-colour
    offsite values can be supported.  These can't really be specified via the
    OFFSITE keyword currently.

Anyone wanting to experiment with this will need to build from CVS (last
changes committed just a few minutes ago).   Feel free to contact me for details.
There are also some contrived examples of the various options in the MSAutoTest
test suite.

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent