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[Dave Beverstock]

From: bever at erim.org (Dave Beverstock)
Subject: Re-Post of Question: What Integer Data Type Does GRASS Use?

I've posted this question to grass-u once and got no response.  I
posted to grass-p once and got no response either. I realize that
there may be some communication failure from me to the list, and so I
repost.  I am sincerely interested in an answer, and the answer is not
evident to me.  I would appreciate an informative response.  If I am
violating some grass-list etiquette please inform me.

I have Landsat TM data, Band 5 and 7.  I refer to the r.mpacalc
tutorial manual that came with the 4.1(beta?) release. Following the
tutorial I use r.mapcalc to scale the two bands. The tutorial states
that the raster image is stored as an integer file.  What is the data
format of the resulting new raster image ?  Is it signed or unsigned 8
bit, 16 bit, 32 bit integers?

EG: mapcalc> img1 = ((2.95*tmb.5) + (4.2*tmb.7)) - float(30)

I am concerned because somewhere I thought I read that GRASS stores
raster images as unsigned 8 bit words (0-255), and it's quite possible
that the equation above could generate negative numbers which would be
then probably clipped to 0.

If this is the case is there an alternative data type I can select?

dave

bever at erim.org