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<div class="moz-cite-prefix">It all depends on the data your having
gdal_polygonize contour ...<br>
<br>
here is a snippet of what I'm doing with a csv I'm creating of
current weather<br>
<br>
/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<br>
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<br>
<br>
and then the resulting shapefile is used to create the following<br>
<a class="moz-txt-link-freetext" href="http://www.michiganwxsystem.com/maps/curfore/">http://www.michiganwxsystem.com/maps/curfore/</a><br>
<br>
I have messed around with the 'power' and 'smoothing' settings
these seem the remove the stair steps quite well<br>
<br>
<br>
<pre class="moz-signature" cols="72">-----------------------------------------------------
-Jeff Lake
MichiganWxSystem.com
AllisonHouse.com
TheWeatherCenter.net
GRLevelXStuff.com</pre>
On 2/19/2013 15:12, Jeff Lacoste wrote:<br>
</div>
<blockquote
cite="mid:CAFOE_Bc406dDzoUhAQEQzZQ1C8ZAZhHN10ZT=bnv5_qUT00RNA@mail.gmail.com"
type="cite">
<div dir="ltr">Yes visually attractive or smooth polygons is the
goal. Thanks again Frank.
<div><br>
</div>
<div style="">Doing a web search about simplification algorithm
i found one named '<b
style="font-size:13px;color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px">Ramer-Douglas–Peucker'
(</b><a moz-do-not-send="true"
href="http://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm">http://en.wikipedia.org/wiki/Ramer-Douglas-Peucker_algorithm</a>).</div>
<div style="">It appears that 'Geos'' library implement this
algorithm. Is this algorithm exposed through OGR ?</div>
<div style=""><br>
</div>
<div style="">Could this algorithm help smoothing a polygon
without necessary make the new nodes too far from the original
one ? Or may be there</div>
<div style="">are other *more* recommended algorithms ?</div>
<div style=""><br>
</div>
<div>If any one could suggest a simplification algorithm or had
some experience with smoothing polygons, I appreciate their
input.</div>
<div><br>
</div>
<div>Thanks</div>
<div><br>
</div>
<div>Jeff<br>
<div><br>
</div>
<div><br>
</div>
</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Tue, Feb 19, 2013 at 2:42 PM, Frank
Warmerdam <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:warmerdam@pobox.com" target="_blank">warmerdam@pobox.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">On Tue, Feb 19, 2013 at 11:28 AM, Jeff
Lacoste<br>
<<a moz-do-not-send="true"
href="mailto:jefflacostegdal@gmail.com">jefflacostegdal@gmail.com</a>>
wrote:<br>
> Hi Frank,<br>
><br>
> Thanks for your quick response. Following the edges
of the pixels seems a<br>
> perfect solution for non continuous grid (ex. land
use, etc.) as<br>
> the boundary between the class is important to keep
when constructing the<br>
> polygon. However for continuous grid (.ex
elevations), the boundaries are<br>
> a bit not clear and not clear cut. When following the
pixels edges, the<br>
> created polygons appear to have the stairs effect and
are less visually<br>
> attractive.<br>
><br>
> I thought of a smoothing the polygons to not have
*rough* edges using the<br>
> current gdal_polygonize by trying to not follow the
pixels edges and use<br>
> instead of the<br>
> pixel centers. Basically do something similar to what
contour generator does<br>
> by treating the raster values as continuous.<br>
<br>
</div>
Jeff,<br>
<br>
Ah, I see, you are looking for visually attractive polygons
from<br>
continuous fields.<br>
<br>
I have wondered if it would be reasonable to produce a
version of the<br>
contour generator that actually produces polygon regions.
If we had<br>
that then applying appropriate simplification to the
resulting very<br>
detailed edges should give something attractive and with
reasonable<br>
information density. An appropriate simplification
algorithm might do<br>
this in a reasonable way for the existing polygonize output
but I<br>
don't know enough about the simplification algorithms to
suggest one.<br>
<br>
I don't think aiming for pixel centers in gdal_polygonize
would really<br>
solve the problem.<br>
<div class="HOEnZb">
<div class="h5"><br>
Best regards,<br>
--<br>
---------------------------------------+--------------------------------------<br>
I set the clouds in motion - turn up | Frank
Warmerdam, <a moz-do-not-send="true"
href="mailto:warmerdam@pobox.com">warmerdam@pobox.com</a><br>
light and sound - activate the windows | <a
moz-do-not-send="true"
href="http://pobox.com/%7Ewarmerdam" target="_blank">http://pobox.com/~warmerdam</a><br>
and watch the world go round - Rush | Geospatial
Software Developer<br>
</div>
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