[GRASS-dev] [GRASS-user] r.covar vs layerStats in R

[Markus Metz]

On Tue, Nov 20, 2018 at 7:59 PM Micha Silver <tsvibar at gmail.com> wrote:
>
>
> On 11/19/18 12:41 PM, Markus Neteler wrote:
> > On Sun, Nov 18, 2018 at 10:32 PM Micha Silver <tsvibar at gmail.com> wrote:
> >> I am preparing a correlation matrix for 7 raster layers. The results
using the r.covar module are different from the R layerStats function. I
suspect this is due to handling of null cells. The R function has a
parameter to remove NA cells, but the GRASS module, I think, just loops
over all cells, including no value.
> >>
> >>
> >> Can anyone confirm that GRASS does not deal with null cells, and that
this would cause the difference in correlation results?
> > Here how r.covar treats NULL cells:
> >
> >
https://trac.osgeo.org/grass/browser/grass/trunk/raster/r.covar/main.c#L93
>
> Looking at lines 94 - 100, it seems that the count variable is
> incremented even when a cell value is null.

because of the "continue;", count is not incremented if any cell value is
null

Markus M

>
> Please correct me if I'm wrong.
>
> Since count is used in the calculation of covariance and correlation
> (lines 118-132) shouldn't it contain the number only of cells with value?
>
>
> Thanks
>
> >
> > Markus
>
> --
> Micha Silver
> Ben Gurion Univ.
> Sde Boker, Remote Sensing Lab
> cell: +972-523-665918
>
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