Re: [GRASS-user] r.covar vs layerStats in R
Micha Silver <[email protected]> Tue, 20 Nov 2018 20:59:00 +0200
| Newsgroups | gmane.comp.gis.grass.devel,gmane.comp.gis.grass.user |
|---|---|
| Message-ID | <[email protected]> |
On 11/19/18 12:41 PM, Markus Neteler wrote: > On Sun, Nov 18, 2018 at 10:32 PM Micha Silver <[email protected]> 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. 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 [email protected] https://lists.osgeo.org/mailman/listinfo/grass-dev