Hello Cesar I wouldn't expect pixel resolution to play a role here. The statistics must be carried out over the values. The raster(s) I'm testing are rectangular, without null values. So reprojecting will change the pixel size (from a square to a rectangle), but it will (should) not change the number of pixels.
I'll try in another GRASS version and post the results. best Carlos On Mon, Nov 16, 2015 at 4:48 PM, César Augusto Ramírez Franco < [email protected]> wrote: > Hello Carlos, > > Maybe it has something to do with the pixel resolution? I would certainly > expect the same results, but with a very similar region (i.e. same number > of rows and columns, or at least very close and a similar number of pixels) > > Maybe when projecting the raster, the length of the array is varying but I > wouldn't expect to vary very much, are you getting the same results in a > previous version of GRASS? (7.0 or even 6.4?) > > Greetings > El nov. 16, 2015 11:35 AM, "Carlos Grohmann" <[email protected]> > escribió: > >> Hi all. >> >> I'm analyzing some global-scale DEMs, like ETOPO1/2, SRTM30_PLUS, etc. >> >> I'm getting the statistics for the whole dataset with r.univar, but today >> I noticed that the results differ if I use different projections. (GRASS >> 7.1) >> >> For example, ETOPO2: >> >> Using a latlong pseudo-projection (plate carré) >> >> >> min: -10791 >> max: 8440 >> mean: -1888.6480792 >> median: -2457 >> stddev: 2650.01922839 >> p25: -4273 >> p75: 216 >> >> >> And using equal-area cylindrical: >> >> min: -10791 >> max: 8440 >> mean: -2379.78247747 >> median: -3291 >> stddev: 2507.89668617 >> p25: -4541 >> p75: 94 >> >> >> >> Are these differences expected? I would think that they should be the >> same, regardless of projection (I'm thinking on the elevation values as an >> array of values). >> >> thanks >> >> Carlos >> >> >> >> >> >> -- >> Prof. Carlos Henrique Grohmann >> Institute of Energy and Environment - Univ. of São Paulo, Brazil >> - Digital Terrain Analysis | GIS | Remote Sensing - >> >> http://carlosgrohmann.com >> http://orcid.org/0000-0001-5073-5572 >> ________________ >> Can’t stop the signal. >> >> _______________________________________________ >> grass-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-user >> > -- Prof. Carlos Henrique Grohmann Institute of Energy and Environment - Univ. of São Paulo, Brazil - Digital Terrain Analysis | GIS | Remote Sensing - http://carlosgrohmann.com http://orcid.org/0000-0001-5073-5572 ________________ Can’t stop the signal.
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