Yes visually attractive or smooth polygons is the goal. Thanks again Frank.
Doing a web search about simplification algorithm i found one named '*Ramer-Douglas–Peucker' (*http://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm). It appears that 'Geos'' library implement this algorithm. Is this algorithm exposed through OGR ? Could this algorithm help smoothing a polygon without necessary make the new nodes too far from the original one ? Or may be there are other *more* recommended algorithms ? If any one could suggest a simplification algorithm or had some experience with smoothing polygons, I appreciate their input. Thanks Jeff On Tue, Feb 19, 2013 at 2:42 PM, Frank Warmerdam <warmer...@pobox.com>wrote: > On Tue, Feb 19, 2013 at 11:28 AM, Jeff Lacoste > <jefflacosteg...@gmail.com> 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. > > Jeff, > > Ah, I see, you are looking for visually attractive polygons from > continuous fields. > > I have wondered if it would be reasonable to produce a version of the > contour generator that actually produces polygon regions. If we had > that then applying appropriate simplification to the resulting very > detailed edges should give something attractive and with reasonable > information density. An appropriate simplification algorithm might do > this in a reasonable way for the existing polygonize output but I > don't know enough about the simplification algorithms to suggest one. > > I don't think aiming for pixel centers in gdal_polygonize would really > solve the problem. > > 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 >
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