[GRASSLIST:4247] Re: r.in.gdal help

Markus Neteler neteler at itc.it
Thu Aug 8 02:41:39 EDT 2002

On Thu, Aug 08, 2002 at 12:36:54AM +0100, Glynn Clements wrote:
> Kevin Slover wrote:
> > I am having a little trouble (again) with the r.in.gdal.  Currently, I
> > am trying to import an erdas img file.  It comes in fine, however, it
> > breaks it up into 3 separate files.  The file is supposed to be a map of
> > somesorts.  Any idea on how to recreate this??  Thanks....
> Does it break it up spatially, or into R/G/B colour channels?
> If it's broken up into colour channels, you can generate a composite
> map using r.composite. However, depending upon what you're planning to
> do with it, it may be better to leave it as three separate channels. 
> Generating a composite map may either lose information, or create a
> massive number of categories (and an equally massive colour table), or
> a combination of both.

Short addition: a massive number of categories (and an equally massive
color table) will slow down the map display *significantly*. The
magic number is around 8000 colors, with more than 8000 colors you
face a speed problem for that particular map. Since 8000 colors are
far from 24bit, it's better to keep the channels separated and
compose them on the fly for visual purposes only.

d.rgb and r.composite use per default less than 24bit.



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