Hi, @Nikos: I'll send information about maps tonight. I'll send 'r.describe -r' output also. @Sylvain: Thank you, I didn't noticed the differences, my friend might had done histogram strecthing over results, so this may be the reason for -2/2 thing, I will check this. By the way I'm not sure how we can make data to have same layer extent and dimension in both programs. I didn't do a special thing before calculation, I just used g.region and r.mapcalc methods.
2013/1/14 Sylvain Maillard <[email protected]> > Hi, > > a quick look at the stats files show some differences: > - "Dimensions" > - "Layer Extent" > - not the same range of data (from -2 to 2 in ERDAS ? oO) > > so that's totally logical to get different mean and stdev ... > > take care to use exactly the same extent/res when you are comparing 2 > files ;) > > > cheers, > Sylvain > > > > 2013/1/14 Nikos Alexandris <[email protected]> > >> Gökçen Güner: >> >> > > This will not be a specific GRASS question. My friend and I tried to >> > > calculate NDVIs of same data set and results seem same to us. >> >> What kind of images are those, if I may ask? Which sensor? >> >> > > But checking statistics of each output we saw that statistics are very >> > > different. I mean, median, mean, std.dev values of Grass output and >> Erdas >> > > output are different. >> >> > > We couldn't find an explanation for this situation. What can be >> > > the reason for this? >> >> > There are reasons. For example, different pixel inclusion rules (of >> course I >> > have in mind border-near pixels). Other reasons might be the spatial >> > resolution and extent (remember, GRASS-GIS is strict with that) and the >> > presence of a MASK. >> >> Also, >> >> what about NULL or NoData cells? How does ERDAS deal with them -- I don't >> remember now. How are they defined, if they exist, in your image? >> >> What does "r.describe -r" return for the data set(s) in question? >> >> Thanks, Nikos >> _______________________________________________ >> grass-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-user >> >> > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user > >
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