What Integer Data Type Does GRASS Use?

[Malcolm Williamson]

Dave,
Per the GRASS4.1 Programmer's Manual (a recommended reference!!):
"Each grid cell is stored in the file as one to four 8-bit bytes of data."
"When the data values in the raster file require more than one byte, they are
stored in *big-endian* format, which is to say as a base 256 number with the
most significant digit first."
"Negative values are stored as a signed quantity, i.e., with the highest bit set
to 1:"

To summarize, GRASS supports integer values from -2E+32 to 2E+32. Beware of the 
handling of floating point numbers within GRASS programs!

-- 
Malcolm D. Williamson - Research Assistant       E-mail: malcolm at cast.uark.edu
Center for Advanced Spatial Technologies      Telephone: (501) 575-6159
Ozark Rm. 12                                        Fax: (501) 575-3846 
University of Arkansas              
Fayetteville, AR 72701
> 
> 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
> 
>