[gdal-dev] gdal_polygonize and polygon edges

[Frank Warmerdam]

On Tue, Feb 19, 2013 at 11:28 AM, Jeff Lacoste
<jefflacostegdal at 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,
-- 
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