[postgis-users] Point inside a polygon

[Steve.Toutant at inspq.qc.ca]

Having a centroid outside a polygon is a common situation, even with valid 
geometries.
Depending of use case, I use ST_PointOnSurface when 
ST_Within(St_Centroid(surface), surface) returns false
steve





Rémi Cura <remi.cura at gmail.com>@lists.osgeo.org 
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2014-05-05 07:09
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Re: [postgis-users] Point inside a polygon








Hmm your problem is not about a function, is about using invalid 
geometries !

Why simply don't fix your geometry?
you must do it anyway if you want to use PostGIS 
without strange bugs.

Use http://postgis.refractions.net/docs/ST_MakeValid.html

Cheers,
Rémi-C


2014-05-03 15:51 GMT+02:00 Larry Reeder <lnreeder at gmail.com>:
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.

       -Larry




On Fri, May 2, 2014 at 1:38 PM, Åsmund Tokheim <asmundto at gmail.com> wrote:
Hi

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.

Åsmund


On Fri, May 2, 2014 at 12:45 PM, Nicolas Ribot <nicolas.ribot at gmail.com> 
wrote:
Hi,

Use st_pointOnSurface (
http://postgis.net/docs/manual-2.1/ST_PointOnSurface.html)

Nicolas


On 2 May 2014 06:32, J.Alejandro Martinez Linares <islanis at infomed.sld.cu> 
wrote:
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?

cheers.

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