a few years ago someone had posted some perl code for making polys from the contour output.
the idea was to sort the lines into an m-way tree by contains with the root node being the extent of the data then each node would be outer ring and a copy of the children being the inner rings i have done this myself and it works Brian On Tue, 2013-02-19 at 14:28 -0500, Jeff Lacoste wrote: > Hi Frank, > > > Thanks for your quick response. Following the edges of the pixels > seems a perfect solution for non continuous grid (ex. land use, etc.) > as > the boundary between the class is important to keep when constructing > the polygon. However for continuous grid (.ex elevations), the > boundaries are > a bit not clear and not clear cut. When following the pixels edges, > the created polygons appear to have the stairs effect and are > less visually attractive. > > > I thought of a smoothing the polygons to not have *rough* edges using > the current gdal_polygonize by trying to not follow the pixels edges > and use instead of the > pixel centers. Basically do something similar to what contour > generator does by treating the raster values as continuous. > > > Thanks > > > On Tue, Feb 19, 2013 at 1:44 PM, Frank Warmerdam <warmer...@pobox.com> > wrote: > On Tue, Feb 19, 2013 at 10:29 AM, Jeff Lacoste > <jefflacosteg...@gmail.com> wrote: > > Hi, > > > > I'm using gdal_polygonize.py to create polygon from a grid > and the output > > polygons seems to follow the edges > > of the grid pixels. I was wondering if there is any way to > change/edit the > > code to instead of following the edges > > of the pixels, use the center of the pixels as the nodes of > the created > > polygons ? > > > > So instead of a polygon following the edges of the pixels, > it will instead > > be passing through the center of the connected > > pixels... This is to avoid having a scale effect of > following the pixels > > edges. > > > Jeff, > > With the current algorithm, this is not really possible. > > I am also not clear what it would mean to go from pixel center > to > pixel center. The algorithm attempts to identify the borders > between > regions of different pixel values and turn them into > polygons. What > does it mean to make a polygon boundary that goes through the > center > of a pixel with a particular value? > > Another algorithm you might want to keep in mind is the > contour > generator. It treats the the raster values as a continuous > field, and > builds edges based on linear interpolation between pixel > centers. > This gives a result that could pass through a pixel center if > it > happens to be an exact contour level. > > Best regards, > -- > > ---------------------------------------+-------------------------------------- > I set the clouds in motion - turn up | Frank Warmerdam, > warmer...@pobox.com > light and sound - activate the windows | > http://pobox.com/~warmerdam > and watch the world go round - Rush | Geospatial Software > Developer > > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev -- Brian Case KF7WPK r...@winkey.org _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
