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.
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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