[GRASS-user] Null or 0?

[ALT SHN]

Patrice, Daniel,


Thank you for your commments - it shaded some light on the subject.

Regards,

André Mano

2012/2/5 Patrice Dumas <pertusus at free.fr>

> On Sun, Feb 05, 2012 at 07:22:29AM -0200, Daniel Victoria wrote:
> > Hi Andre,
> >
> > On raster algebra, operations using null will return null while
> operations
> > with 0 behaves like expected. Ex:
> > 12 x null = null
> > 12 x 0 = 0
>
> Also means do not behave the same on NULL, for example when using r.univar
> (according to my understanding of the documentation, haven't tested)
> NULL cells are excluded from the computation, so 1 cell with a value 1
> and 9 NULL will give a mean of 1 while 1 cell with a value 1 and 9 with
> value 0 will give a mean of 0.1.
>
> --
> Pat
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