[postgis-devel] ST_PointOnSurface calculation

Martin Davis mtnclimb at gmail.com
Tue Feb 2 07:23:42 PST 2021


Sure, if you have suggestions for the content.  But we'll try to get to it
soon anyway.

On Mon, Feb 1, 2021 at 10:38 PM Paolo Cavallini <cavallini at faunalia.it>
wrote:

> thanks a lot Martin for the clarification.
> should I open a ticket on the docs?
> cheers.
>
> Il 02/02/21 07:29, Martin Davis ha scritto:
> > Yes, ST_PointOnSurface computes a point which is guaranteed to lie
> > within a polygon.  This is not the case for the centroid, which may lie
> > outside a polygon (e.g the centroid of a C-shaped polygon lies outside
> > the polygon).
> >
> > The description of the algorithm in the GIS-SE question is essentially
> > correct.
> >
> > And yes, improving the documentation page would be good, as well as
> > providing some example diagrams.
> >
> > On Mon, Feb 1, 2021 at 10:15 PM Paolo Cavallini <cavallini at faunalia.it
> > <mailto:cavallini at faunalia.it>> wrote:
> >
> >     Hi all,
> >     the description of the function is scanty. I always assumed it
> >     calculated the point within a polygon closest to the centorid, but I
> >     read it may not be so:
> >
> https://gis.stackexchange.com/questions/76498/how-is-st-pointonsurface-calculated
> >     <
> https://gis.stackexchange.com/questions/76498/how-is-st-pointonsurface-calculated
> >
> >     Is this confirmed?
> >     In case, I suggest describing it in the manpage.
> >     Thanks for any clarification.
> >     Cheers.
> >     --
> >     Paolo Cavallini
> >     www.faunalia.eu <http://www.faunalia.eu> - QGIS.org
> >     training, support, development on QGIS, PostGIS and more
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> >
> >
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>
> --
> Paolo Cavallini
> www.faunalia.eu - QGIS.org
> training, support, development on QGIS, PostGIS and more
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> postgis-devel mailing list
> postgis-devel at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/postgis-devel
>
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