problems w. i.composite, i.points

nick%ikaros at nick%ikaros at
Tue Jun 30 15:58:27 EDT 1992

I am a new user to GRASS and have a couple questions:

1) I have been having problems making composite color images from 
three Landsat MSS bands. I have run i.composite, and specified the three 
data bands. The program seems to run normally and produces a new raster
file which looks relatively normal, but it has too few colors or data values: 
it seems that similar values are being clumped together so that the
resulting image has only a dozen or so different values/colors. The
problem isn't with the monitor -- a histogram and stats of the compostite
map shows just a series of spikes, not a smooth curve.  I tried
rescaling the different bands of data, to make sure that they're all
at the same scale, but the results were about the same (is this necessary
in i.composite, or does it account for differences in scale?) Are there any 
secrets to getting i.composite to produce the clean smooth images I'm 
looking for?

2) Is there a way to rectify MSS and other imagery directly into a 
lat-long coordinate system? I can't get i.points to accept lat-long 
coordinates; it will only take UTM or other x,y coordinates. I could
rectify first into a UTM database and then re-rectify that int lat-long, but 
that seems unnecessarily roundabout. If it is necessary to go through
a UTM database, what is the easiest way to convert from UTM to 
long-lat without having to point again to individual pixels on the image in

I would very much appreciate any help people could offer. Thanks in
advance --

Nick Cahill
Perseus Project
nick at

PS -- forgive me if this has been posted before; we've been having problems
with the mailer here, and I'm not sure what's gotten through and what hasn't.

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