Dear Roger and Micha, Thank you for the reply. I will read carefully your coments, and write back again. Both you clarified some interesting points to me.
cheers, milton brazil=toronto 2009/6/10 Micha Silver <[email protected]> > Hello Milton > > Roger's answer was, as always, both complete and to the point. > > As a further exercise, I took a small region of 540000 cells with floating > point values, and using the "feature=area" option to r.to.vect I created a > vector map of polygons. It produced over 360000 polygons. Most will be > polygons of 1 cell in size (from the original raster). I assume that's *not* > what you're looking for... > > -- > > Micha > > > > Roger Bivand wrote: > > I think that r.to.vect wants to build a line structure, like river >> channels, >> but sees all the raster cells occupied, so no linear structure, and the >> advice to thin first is then appropriate. If this is connected to your >> question about calculating a measure of spatial autocorrelation for the >> raster data, then I suspect that you do not need polygons but rather >> points, >> where r.out.xyz may be helpful, followed by v.in.ascii if you will be >> using >> GRASS downstream, or if you want to emit a shapefile for GeoDa (another >> posting). >> >> If you really want to calculate a measure of spatial autocorrelation for >> your raster, I suggest copying the raster to R with readRAST6, creating >> the >> neighbour list with dnearneigh() with max. distance the greater of ewres >> and >> nsres, and proceeding from there in the usual way. But please consider the >> inevitable fact that unless the resolution of your raster matches the >> "natural" support of the phenomenon of interest, the observed >> autocorrelation will certainly be driven by your having multiple >> neighbouring "observations" of each "entity", in addition to not having >> demeaned (detrended) the data. This means that any results will almost >> certainly be spurious. >> >> Hope this helps, >> >> Roger >> >> >> Milton Cezar Ribeiro wrote: >> >> >>> Dear Grass-Gurus, >>> >>> I have a 2400x2200 raster image with values ranging >>> from 0.1 to 42, in float format. Now I need >>> vetororize the image, on the way that each pixel >>> come to be a polygon and the pixel value be stored as >>> attribute. >>> >>> I am trying to do this using: >>> r.to.vect input=temp71.img output=temp71_img_integer_vect_200m --o -b >>> >>> but grass return the following error messages: >>> >>> GRASS 6.4.0svn (newLocation):C:/GRASS-6-SVN/msys/home/mjfortin > >>> r.to.vect >>> inpu >>> t=temp71.img output=temp71_img_integer_vect_200m --o -b >>> WARNING: Vector map <temp71_img_integer_vect_200m> already exists and >>> will >>> be overwritten >>> WARNING: Table <temp71_img_integer_vect_200m> linked to vector map >>> <temp71_img_integer_vect_200m> does not exist >>> Extracting lines... >>> ERROR: Raster map is not thinned properly. >>> Please run r.thin. >>> By the way, I am running grass under a WinXp 64bit. >>> Any help are welcome. >>> >>> Cheers >>> >>> milton >>> brazil=toronto >>> >>> _______________________________________________ >>> grass-user mailing list >>> [email protected] >>> http://lists.osgeo.org/mailman/listinfo/grass-user >>> >>> >>> >>> >> >> >> ----- >> Roger Bivand >> Economic Geography Section >> Department of Economics >> Norwegian School of Economics and Business Administration >> Helleveien 30 >> N-5045 Bergen, Norway >> >> >> > >
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