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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