[GRASS5] r.mapcalc and NULL question

Justin Hickey jhickey at hpcc.nectec.or.th
Tue Jan 16 03:44:39 EST 2001

Hi Markus

Markus Neteler wrote:
> Generally I consider this as a bug because you can't always know if
> a map contains NULLs. If only a few pixels would be nulls you may
> use option 2 and don't realize that the result is not want you want.
> I feel this behaviour is somewhat dangerous. The isnull() is useful,
> but if you have to apply it on default in if-clauses, it's a bit 
> annoying.
> Other comments?

I agree with the others, it is not a bug. Perhaps r.mapcalc should print
a warning if it tries to perform arithmetic on null values. At least
then, the user will be notified of the problem.


Jazzman (a.k.a. Justin Hickey)  e-mail: jhickey at hpcc.nectec.or.th
High Performance Computing Center
National Electronics and Computer Technology Center (NECTEC)
Bangkok, Thailand
People who think they know everything are very irritating to those
of us who do.  ---Anonymous

Jazz and Trek Rule!!!

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