[GRASS-dev] r.mapcalc 32-bit ceiling

Rainer M Krug r.m.krug at gmail.com
Fri Nov 25 04:59:12 EST 2011

On Fri, Nov 25, 2011 at 4:31 AM, Andy Wickert <andrewwickert at gmail.com>wrote:

> Hi Grass-dev,
> I ran into an unexpected issue (to me, at least) with r.mapcalc:
> I was multiplying and dividing by some pretty big scalars, and one of
> those was greater than a 32-bit signed value (so >2**31). What mapcalc
> did was to reduce that value to 2**31 and carry on with operations.
> There was no warning, and I didn't find any information about this on
> the r.mapcalc help page, so I just wanted to alert (or possibly
> remind) the list that this exists and note that (as a non-developer)
> it took me a while to figure out that this was a problem. If there is
> an easy way to throw an error instead of silently hitting a ceiling,
> or this would be important enough to put on the manual webpage, I
> think it would be helpful, and certainly would have saved me a ton of
> time.

I ran into the same issue when I was using integers - I solved it by
converting the raster to double. But I agree with Andy: I think GRASS
should throw an error when the rollover occurs, or use a dedicated value in
this cell, so that one can check afterwards. Thinking about it: an error is
asked for, as something went wrong.



> Thanks, and happy Thanksgiving to those in the USA!
> Andy
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Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology,
UCT), Dipl. Phys. (Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

Tel :       +33 - (0)9 53 10 27 44
Cell:       +33 - (0)6 85 62 59 98
Fax (F):       +33 - (0)9 58 10 27 44

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email:      Rainer at krugs.de

Skype:      RMkrug
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