On Tue, Nov 20, 2018 at 7:59 PM Micha Silver <tsvi...@gmail.com> wrote: > > > On 11/19/18 12:41 PM, Markus Neteler wrote: > > On Sun, Nov 18, 2018 at 10:32 PM Micha Silver <tsvi...@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 > > _______________________________________________ > grass-dev mailing list > grass-...@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-dev
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