The program is not shifting the pixels, but the program does assume the pixels to be points and not rectangular areas so maybe I will have to shift the pixels. Do you know what transformation I would need to use?
Jack. -- mathuin at gmail dot com On Tue, Aug 19, 2014 at 7:17 PM, Chaitanya kumar CH <[email protected]> wrote: > Jack, > The GDALPolygonize algorithm draws the polygon edges along the pixel edges. > It assumes the pixels to be rectangular areas instead of points. > In the example you described, the first polygon should contain four vertices > with the pixel in the centre. > Make sure that the program you are using to display them is not shifting the > pixels. > > On 20 Aug 2014 07:12, "John Twilley" <[email protected]> wrote: >> >> I am trying to use GDAL's polygonize algorithms to help me identify >> regions in landcover data. I made a trivial example, but I am having >> trouble understanding the results that I get, nor can I determine how >> to get the results I want. >> >> Given the following raster: >> >> 11 11 11 11 11 >> 11 11 11 11 11 >> 11 11 12 11 11 >> 11 11 11 11 11 >> 11 11 11 11 11 >> 11 11 11 11 11 >> >> If I were to polygonize this raster, I would expect two polygons: one >> which contains the single point 12, and another with an outer ring was >> the perimeter of the raster and an inner ring circling the single >> point 12. I would also expect that the first polygon would contain >> the single point 12 and that the second polygon would contain all the >> points 11. >> >> Instead, what I got was a polygon starting from the single point 12 >> and extending down and to the right one pixel, and another polygon >> with an outer ring that went off the down and right edges and an inner >> ring equal to the first polygon's outer ring. The first polygon >> doesn't actually contain any points and the second one doesn't contain >> any points on either ring but does contain all the other points. >> >> What do I need to do to get the results I am expecting? >> >> Jack. >> -- >> mathuin at gmail dot com >> _______________________________________________ >> gdal-dev mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/gdal-dev _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
