[GRASSLIST:5538] Re: A problem with computation in r.mapcalc

[Miha STAUT]

>Miha STAUT wrote:
>
> > I have a problem computing this with r.mapcalc:
> >
> > r.mapcalc < avg # piping
> > avg=10*log((
> > 10^(rast1/10-12)*6.863636
> > +10^(rast2/10-12)*2.909091
> > +10^(rast3/10-12)*3.742424
> > +10^(rast4/10-12)*2.333333
> > +10^(rast5/10-12)*2.318182
> > +10^(rast6/10-12)*3.590909
> > +10^(rast7/10-12)*0.969697
> > +10^(rast8/10-12)*2.435484
> > )
> > *10^12/30.84457
> > ,10)
> >
> > The process of computing seems to finish OK, but the new map gives only 
>NAs.
> > Why can that be? The problem appearently lies in the 10^rast. All the
> > rasters have values between 0 and 140. The final map should not have
> > excessively high values.
> >
> > How should I surround the problem?
>
>First, I suggest converting all of the literals to floating-point,
>e.g.
>
> > *10.0^12.0/30.84457
>
>An expression such as "10^12" will be computed using integer
>arithmetic, which is likely to result in an overflow.
>
>--
>Glynn Clements <glynn.clements at virgin.net>

Thanks Glynn and all the others, it worked.

Miha Staut


_________________________________________________________________
The new MSN 8: smart spam protection and 2 months FREE*  
http://join.msn.com/?page=features/junkmail