[postgis-devel] ST_PointOnSurface calculation

[Imre Samu]

> I've updated the manual page

Thanks !

> Any further suggestions?  (Diagrams would be good, I know)

just for brainstorming, from a beginner mind.
No problem if these ideas are rejected.

#1.
Adding  ST_MaximumInscribedCircle  to the "See also"
     reason:  in my mind  -  this is similar like the  "Circle on Polygon"
problem

#2.
in the tutorial page [1]  19.1. ST_Centroid / ST_PointOnSurface
 .. there is an example diagram, maybe it can be reused ...
[1]
https://postgis.net/workshops/postgis-intro/geometry_returning.html#st-centroid-st-pointonsurface
or it is possible to crosslink the tutorial page [1] ?

#3. reusing the geometry from [1] .. we can create an example ..
   when the  ~3 center like example is different.

SELECT
  ST_AsText(ST_Centroid(geom)) AS "centroid",
  ST_AsText(ST_PointOnSurface(geom)) AS "pointOnSurface",
  ST_AsText((SELECT center FROM ST_MaximumInscribedCircle(geom))) AS
"center_maximumInscribedCircle" -- postgis >= 3.1 Geos >=3.9
FROM (VALUES
    ('POLYGON ((30 0, 30 10, 10 10, 10 40, 30 40, 30 50, 0 50, 0 0, 0 0, 30
0))'::geometry)
  ) AS t(geom);
+------------------------------+----------------+-------------------------------+
|           centroid           | pointOnSurface |
center_maximumInscribedCircle |
+------------------------------+----------------+-------------------------------+
| POINT(11.666666666666666 25) | POINT(5 25)    | POINT(5.859375 5.859375)
     |
+------------------------------+----------------+-------------------------------+
(1 row)

Regards,
   Imre


Martin Davis <mtnclimb at gmail.com> ezt írta (időpont: 2021. febr. 4., Cs,
1:41):

> I've updated the manual page:
> https://postgis.net/docs/manual-dev/ST_PointOnSurface.html
>
> Any further suggestions?  (Diagrams would be good, I know)
>
> On Mon, Feb 1, 2021 at 10:15 PM Paolo Cavallini <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
>> Is this confirmed?
>> In case, I suggest describing it in the manpage.
>> Thanks for any clarification.
>> Cheers.
>> --
>> Paolo Cavallini
>> www.faunalia.eu - QGIS.org
>> training, support, development on QGIS, PostGIS and more
>> _______________________________________________
>> postgis-devel mailing list
>> postgis-devel at lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/postgis-devel
>>
> _______________________________________________
> postgis-devel mailing list
> postgis-devel at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/postgis-devel
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/postgis-devel/attachments/20210204/3b4cfc43/attachment.html>