[GRASSLIST:4284] Re: more gdal help!

Kevin Slover kevin.slover at noaa.gov
Tue Aug 13 14:43:45 EDT 2002

    mission accomplished.  What was happening was that when I imported the
.img file with r.in.gdal, it was assigning a color scale to it.  I went in
and edited the colr table, using vi, and then had to run r.support to create
a histogram.  And voila, using d.rgb, it displayed correctly.

I am not sure, of course, what the usefullness of the r.composite tool.  It
fails to correctly display the image I was shooting for.  I know in other
programs (manifold) that you use a composite type function to piece together
the rgb values.

Thanks for the info, now, off to bigger and better? files...

Glynn Clements wrote:

> Kevin Slover wrote:
> > Thanks to everyone with the previous response for creating a composite
> > image.  i.composite worked the best, however is still not completely
> > working for me.  I would say there was a problem with the file, but we
> > are able to process it with another program, just takes hours to
> > manipulate.
> >
> > The problem that I am having is that there doesn't seem to be much color
> > variation.  How do I explain this.  Example, the United States
> > background color is a bright yellow.  It should be a softer yellow, with
> > different shades.  Not happening.  I have tried a variety of color
> > levels, from 2 (min) to 6/7 (for 256 colors) and all the way to 500.
> > None have worked.
> First, check the range of the actual data, with r.info.
> Second, check the images' colour tables, either visually with
> d.legend, or by examining the file in the mapset's "colr" directory.
> This should be a grey scale, where black (0 or 0:0:0) corresponds to
> zero and white (255 or 255:255:255) corresponds to the maximum
> possible value (e.g. 255 for 8-bit data).
> Then, try displaying the data with d.rgb, or exporting it to a PPM
> file (with r.out.ppm3) and viewing the PPM file.
> Also, I'm curious as to your reason for generating a composite map.
> I've yet to hear of a good reason for using them (I'm not saying that
> there aren't reasons, just that I don't currently know of any).
> --
> Glynn Clements <glynn.clements at virgin.net>

LTJG Kevin Slover, NOAA
GIS Specialist/Meteorologist/Oceanographer
Tropical Prediction Center/Technical Support Branch
11691 SW 17th Street Miami FL 33165
(W) 305-229-4456  (F) 305-553-1264

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