[GRASS5] status of libgrass, mapserver, gdal and >8bit rasters

Frank Warmerdam warmerdam at pobox.com
Sat Mar 13 14:32:54 EST 2004

Stephan Holl wrote:
> Dear developers,
> after some testing using the (quite outdated) libgrass-version with
> gdal, grass and mapserver I would like to know, if there are some
> initiatives to make libgrass/gdal support more than 256 colors. I am no
> programmer but I like to know if this would be a big deal to implement
> (because I am strongly interested in using it).
> It would be a real benefit for the interaction with mapserver, if
> raster-support directly from a a GRASS-Location could be possible, I
> think. 
> Perhaps anybody from the core-developers could give some comments on
> this topic.


It what sense would you like to support >8bit rasters?  The GDAL access to
GRASS rasters via libgrass already supports floating point rasters, and
integer rasters with >8 bit pixel data types.  There may (or may not, I'm
not too sure) be a limit only 256 colors in the driver though that isn't
a requirements of GDAL.

Is the issue at the MapServer end?  MapServer has supported >8bit rasters
for a while, but by scaling them to 8bit.  I very recently implemented support
in mapserver to apply "true" classification to original >8bit rasters and this
would apply to GRASS rasters as well.  One thing that does not work in MapServer
at this time is use of more than 256 colors in a color table taken from a
GDAL datasource.  So if you want to render an integer grass coverage that
has more than 256 values you are still going to have a problem.  I could look
into correcting this but it hasn't been high priority.

Then there is the more general question of whether I will be updating libgrass
to catch up to more modern GRASS versions. I am not actually aware of any
changes in GRASS raster support that would need an update of libgrass, but it
is my hope to modernize it at some point.  Quite possibly in the near future
everything provided by libgrass will be provided in the core GRASS shared
libraries (libgis, etc) in a way suitable to replace the seperate libgrass.

Best regards,
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

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