It all depends on the data your having gdal_polygonize contour ...
here is a snippet of what I'm doing with a csv I'm creating of current
weather
/usr/local/bin/gdal_grid -zfield "temp" -a
invdist:power=2.0:smoothing=1:nodata=-9999 -outsize 800 600 -l temp
/var/www/html/metar/temp.vrt /var/www/html/metar/temp.tif
python /usr/local/bin/gdal_polygonize.py /var/www/html/metar/temp.tif -f
"ESRI Shapefile" /var/www/html/metar/temp/temp.shp temp temp
and then the resulting shapefile is used to create the following
http://www.michiganwxsystem.com/maps/curfore/
I have messed around with the 'power' and 'smoothing' settings these
seem the remove the stair steps quite well
-----------------------------------------------------
-Jeff Lake
MichiganWxSystem.com
AllisonHouse.com
TheWeatherCenter.net
GRLevelXStuff.com
On 2/19/2013 15:12, Jeff Lacoste 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
<mailto:warmer...@pobox.com>> wrote:
On Tue, Feb 19, 2013 at 11:28 AM, Jeff Lacoste
<jefflacosteg...@gmail.com <mailto: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 <mailto:warmer...@pobox.com>
light and sound - activate the windows |
http://pobox.com/~warmerdam <http://pobox.com/%7Ewarmerdam>
and watch the world go round - Rush | Geospatial Software Developer
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