Hi Rainer,
Thanks a lot for your reply. The problem is indeed that the result of
the calculation does not fit into the variable and your answer made me
realize I had to take a closer look at what happens inside the formula.
As it turns out, the problem lies in the following part of the formula:
round(C/0.0001)
The output of round() is an integer and c/0.0001 gives values that are
larger then the maximum number for integer layers (which I presume is
(2^31)-1). So I need to rethink the formula and the use of round.
Paulo
On 05/15/2013 03:51 PM, Rainer M. Krug wrote:
Paulo van Breugel <p.vanbreu...@gmail.com> writes:
Hi,
I am having trouble with the following computation, which gives me an overflow
warning ("WARNING: Overflow occured in the
calculation").
oerflow usually means that the result of a calculation does not fit into
the variable type selected, i.e. is either smaller then the smallest
value which can be stored or larger then the largest value.
GRASS uses FCELL (float) and DCELL (double) varisbles, where double can
store a larger range (sorry - I don't have the actual values at hand).
You should be able to do the calculations by explicitely converting the
result to double by using the double() function:
UNTESTED:
r.mapcalc "A = if(B==0, double(
(round(C/0.0001)-1175699902)/(3007966667-1175699902) *100.0 ), 1) " --overwrite
should work, although untested.It is possible, thet the conversion to
double needs to be made inside the calculation, depending where the
actual overflow occurs.
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.
Yes - overflow is a warning only, but *usually* results in wrong
results! I fell in that trap once and it took me some time to figure out
what was going on, as, if I remember correctly, no warning was issued
(GRASS 6.4?).
Cheers,
Rainer
I am running GRASS 7.0 on Ubuntu 13.04 64 bit.
Best
Paulo
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--
Paulo van Breugel
Department of Geosciences and Natural Resource Management
Section of Forest, Nature and Biomass
University of Copenhagen
Rolighedsvej 23
1958 Frederiksberg C
Phone: +45 353-31646
Phone: +31 6 12189147
e-mail: p...@life.ku.dk
e-mail: p.vanbreu...@gmail.com
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