Thank you Frank ! Very much appreciated. I'll give 'Simplify' option a try.
Jeff On Tue, Feb 19, 2013 at 3:25 PM, Frank Warmerdam <warmer...@pobox.com>wrote: > Jeff, > > I believe this is exposed in ogr2ogr using the -simplify argument: > > -simplify tolerance: > (starting with GDAL 1.9.0) distance tolerance for simplification. > Note: the algorithm used preserves topology per feature, in particular > for polygon geometries, but not for a whole layer. > > Best regards, > Frank > > On Tue, Feb 19, 2013 at 12:12 PM, Jeff Lacoste > <jefflacosteg...@gmail.com> wrote: > > 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 > > > > > > > > -- > > ---------------------------------------+-------------------------------------- > 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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