[GRASS-dev] Overflow warning in r.mapcalc calculation

[Rainer M Krug]

On Wednesday, May 15, 2013, Glynn Clements wrote:

>
> Paulo van Breugel wrote:
>
> > I am having trouble with the following computation, which gives me an
> > overflow warning ("WARNING: Overflow occured in the calculation").
> >
> > r.mapcalc "A = if(B==0,
> (round(C/0.0001)-1175699902)/(3007966667-1175699902) *100.0, 1)" --overwrite
> >
> >
> > whereby C is a map with values between 1 and 31000. It seems to be
> > related to the size of the numbers (no warning if I divide C by 0.001),
> > but I am not clear what limit I am hitting here or how to avoid this.
> >
> > The warning does not stop the calculation, and the resulting map seems
> > to be correct. However, I rather avoid this warning, also because the
> > warning message causes problems when running in batch from within R.
>
> The round() function always returns an integer, regardless of its
> argument types. Integers are always 32-bit, so the result is limited
> to the range +/- 2147483647 (2^31-1).


True - but is there an equivalent function to round numbers outside the
integer range? Would be useful. Looking at the functions in r.mapcalc, I
can't think of a way of doing this?

Rainer


>
> --
> Glynn Clements <glynn at gclements.plus.com <javascript:;>>
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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

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