[GEOS] #840: PointOnSurface strange behavior

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[GEOS] #840: PointOnSurface strange behavior

geos-2
#840: PointOnSurface strange behavior
------------------------+----------------------------
 Reporter:  sbe         |      Owner:  geos-devel@…
     Type:  defect      |     Status:  new
 Priority:  minor       |  Milestone:  3.6.3
Component:  Default     |    Version:  3.6.2
 Severity:  Unassigned  |   Keywords:  pointOnSurface
------------------------+----------------------------
 Hi all,

 Using Postgis's ST_PointOnSurface, i've got some weird results in recent
 version of Postgis (> 2.0).

 See that image :
 [[Image(https://imagebin.ca/v/3YWtCXtT5lHs)]]


 I would like to know how the PointOnSurface is calculated, and why there
 are so much differences between polygon A,B and C.

 With Postgis 1.5 it was working fine (i.e. the PointOnSurface for my
 polygons were at almost the same place than the Centroids)

 Thank you.

 Sylvain b.

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/840>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #840: PointOnSurface strange behavior

geos-2
#840: PointOnSurface strange behavior
----------------------------+---------------------------
 Reporter:  sbe             |       Owner:  geos-devel@…
     Type:  defect          |      Status:  new
 Priority:  minor           |   Milestone:  3.6.3
Component:  Default         |     Version:  3.6.2
 Severity:  Unassigned      |  Resolution:
 Keywords:  pointOnSurface  |
----------------------------+---------------------------
Changes (by sbe):

 * Attachment "point_on_surface.png" added.


--
Ticket URL: <https://trac.osgeo.org/geos/ticket/840>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #840: PointOnSurface strange behavior

geos-2
In reply to this post by geos-2
#840: PointOnSurface strange behavior
----------------------------+---------------------------
 Reporter:  sbe             |       Owner:  geos-devel@…
     Type:  defect          |      Status:  new
 Priority:  minor           |   Milestone:  3.6.3
Component:  Default         |     Version:  3.6.2
 Severity:  Unassigned      |  Resolution:
 Keywords:  pointOnSurface  |
----------------------------+---------------------------

Comment (by mloskot):

 WKT of your geometries would be helpful

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/840#comment:1>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #840: PointOnSurface strange behavior

geos-2
In reply to this post by geos-2
#840: PointOnSurface strange behavior
----------------------------+---------------------------
 Reporter:  sbe             |       Owner:  geos-devel@…
     Type:  defect          |      Status:  new
 Priority:  minor           |   Milestone:  3.6.3
Component:  Default         |     Version:  3.6.2
 Severity:  Unassigned      |  Resolution:
 Keywords:  pointOnSurface  |
----------------------------+---------------------------

Comment (by sbe):

 Here are the WKT:

 {{{
 A:POLYGON((182111.031940953 141935.935903267,181944.315698016
 141813.663222482,181993.426552077 141735.161360171,182025.215323227
 141755.058841504,182042.126877935 141723.338145732,182089.035943744
 141755.453352846,182096.699289843 141744.892410235,182142.107084301
 141773.967727472,182140.268233846 141825.482203511,182123.233970367
 141827.369156254,182111.031940953 141935.935903267))

 B:POLYGON((182512.231897141 141935.935903267,182344.315698016
 141813.663222482,182393.426552077 141735.161360171,182425.215323227
 141755.058841504,182442.126877935 141723.338145732,182489.035943744
 141755.453352846,182496.699289843 141744.892410235,182542.107084301
 141773.967727472,182540.268233846 141825.482203511,182522.034014178
 141825.369229273,182512.231897141 141935.935903267))

 C:POLYGON((182635.760119718 141846.477712277,182826.153168283
 141974.473039044,182834.952846998 141857.67730337,182862.151853936
 141851.277537031,182860.551912351 141779.280165725,182824.553226698
 141748.881275618,182814.953577191 141758.480925126,182766.155358861
 141721.682268681,182742.156235092 141744.881421657,182692.558045971
 141716.882443927,182635.760119718 141846.477712277))
 }}}

 Projection: srid= 31370

 Thanks.

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/840#comment:2>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #840: PointOnSurface strange behavior

geos-2
In reply to this post by geos-2
#840: PointOnSurface strange behavior
----------------------------+---------------------------
 Reporter:  sbe             |       Owner:  geos-devel@…
     Type:  defect          |      Status:  new
 Priority:  minor           |   Milestone:  3.6.3
Component:  Default         |     Version:  3.6.2
 Severity:  Unassigned      |  Resolution:
 Keywords:  pointOnSurface  |
----------------------------+---------------------------

Comment (by mloskot):

 FWIW, `ST_PointOnSurface` returns **an arbitrary point**. The only
 guarantee is that such point is located inside interior of a geometry.
 Subsequent calls of `ST_PointOnSurface` for the same geometry might
 possibly return different points (all inside the interior, of course).

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/840#comment:3>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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Re: [GEOS] #840: PointOnSurface strange behavior

geos-2
In reply to this post by geos-2
#840: PointOnSurface strange behavior
----------------------------+---------------------------
 Reporter:  sbe             |       Owner:  geos-devel@…
     Type:  defect          |      Status:  new
 Priority:  minor           |   Milestone:  3.6.3
Component:  Default         |     Version:  3.6.2
 Severity:  Unassigned      |  Resolution:
 Keywords:  pointOnSurface  |
----------------------------+---------------------------

Comment (by mloskot):

 FYI, added the three similar polygons to the tests
 https://git.osgeo.org/gogs/geos/geos/commit/64e823b26bc6a771571f39af245b0e0f4e256df8

--
Ticket URL: <https://trac.osgeo.org/geos/ticket/840#comment:4>
GEOS <http://trac.osgeo.org/geos>
GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS).

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