<div dir="ltr"><div><div><div><div>Oops my bad :-/<br><br></div>I use <a href="http://postgis.refractions.net/docs/ST_StartPoint.html">http://postgis.refractions.net/docs/ST_StartPoint.html</a> for this kind of stuff,<br></div>
<br>it is fast but the point may not be "within" enough for you<br>(<a href="http://en.wikipedia.org/wiki/DE-9IM">http://en.wikipedia.org/wiki/DE-9IM</a>)<br></div><br>Cheers,<br></div>Rémi-C<br></div><div class="gmail_extra">
<br><br><div class="gmail_quote">2014-05-05 17:10 GMT+02:00 <span dir="ltr"><<a href="mailto:Steve.Toutant@inspq.qc.ca" target="_blank">Steve.Toutant@inspq.qc.ca</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<p><font face="sans-serif">Having a centroid outside a polygon is
a common situation, even with valid geometries.</font>
</p><p><font face="sans-serif">Depending of use case, I use </font><font size="3">ST_PointOnSurface</font><font face="sans-serif">
when </font><font size="3">ST_Within(St_Centroid(surface), surface) returns
false</font>
</p><p><font size="3">steve</font>
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<p><font face="sans-serif" size="1">2014-05-05 07:09</font>
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<div align="right"><font face="sans-serif" size="1">Objet</font></div>
</td><td><font face="sans-serif" size="1">Re: [postgis-users] Point inside a polygon</font></td></tr></tbody></table>
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<br><font size="3">Hmm your problem is not about a function, is about using
invalid geometries !</font>
<br><font size="3"><br>
Why simply don't fix your geometry?</font>
<br><font size="3">you must do it anyway if you want to use PostGIS <br>
without strange bugs.<br>
</font>
<br><font size="3">Use </font><a href="http://postgis.refractions.net/docs/ST_MakeValid.html" target="_blank"><font color="blue" size="3"><u>http://postgis.refractions.net/docs/ST_MakeValid.html</u></font></a><font size="3"><br>
</font>
<br><font size="3">Cheers,<br>
Rémi-C</font>
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<br><font size="3">2014-05-03 15:51 GMT+02:00 Larry Reeder <</font><a href="mailto:lnreeder@gmail.com" target="_blank"><font color="blue" size="3"><u>lnreeder@gmail.com</u></font></a><font size="3">>:</font>
<br><font size="3">Another thing to be aware of with ST_PointOnSurface is
it can return a point that's on the boundary of polygon, but *not inside*
the polygon, so that ST_Within(St_PointOnSurface(surface), surface) returns
false. That's bitten me before, but may be OK for your purposes.</font>
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<br><font color="#888888" size="3"> -Larry</font>
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<br><font size="3">On Fri, May 2, 2014 at 1:38 PM, Åsmund Tokheim <</font><a href="mailto:asmundto@gmail.com" target="_blank"><font color="blue" size="3"><u>asmundto@gmail.com</u></font></a><font size="3">>
wrote:</font>
<br><font size="3">Hi</font>
<br>
<br><font size="3">You can use st_closestpoint(geom, st_centroid(geom)) to
make sure that the returned point is in most circumstances at or near the
centroid, and always at least on the boundary of the polygon. While st_pointonsurface
certainly will be faster, it will often choose a more random point on the
surface.</font>
<br>
<br><font color="#888888" size="3">Åsmund</font>
<br><font size="3"><br>
</font>
<br><font size="3">On Fri, May 2, 2014 at 12:45 PM, Nicolas Ribot <</font><a href="mailto:nicolas.ribot@gmail.com" target="_blank"><font color="blue" size="3"><u>nicolas.ribot@gmail.com</u></font></a><font size="3">>
wrote:</font>
<br><font size="3">Hi,</font>
<br>
<br><font size="3">Use st_pointOnSurface (</font><a href="http://postgis.net/docs/manual-2.1/ST_PointOnSurface.html" target="_blank"><font color="blue" size="3"><u>http://postgis.net/docs/manual-2.1/ST_PointOnSurface.html</u></font></a><font size="3">)</font>
<br>
<br><font color="#888888" size="3">Nicolas</font>
<br><font size="3"><br>
</font>
<br><font size="3">On 2 May 2014 06:32, J.Alejandro Martinez Linares <</font><a href="mailto:islanis@infomed.sld.cu" target="_blank"><font color="blue" size="3"><u>islanis@infomed.sld.cu</u></font></a><font size="3">>
wrote:</font>
<br><font size="3">Hi people, i need your help, i was using st_centroid to
get a point that be inside a polygon butr st_centroid got a property that
is a problem to me, it returns a point that not always is inside the polygon,
cause when the polygon has an irregular form, the point that st_centroid
is outside the polygon, and i need a function that do a similar thing that
st_centroid but i need that the point it returns always be inside the polygon,
is there a function that do that?<br>
<br>
cheers.<br>
<br>
--<br>
<br>
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