[postgis-users] Centroid Calculation Error???

[Martin Davis]

Thanks, Duster.

JTS (and presumably GEOS) returns POINT (593910.9988377226 226906.23058975482) as the centroid.  Visually, this looks correct (like the centre of mass).

Over to you, DB...

Martin Davis, Senior Technical Architect
Vivid Solutions Inc.
Suite #1A-2328 Government Street   Victoria, B.C.   V8T 5G5
Phone: (250) 385 6040 - Local 308      Fax: (250) 385 6046



> -----Original Message-----
> From: Düster Horst [mailto:Horst.Duester at bd.so.ch]
> Sent: Tuesday, October 28, 2003 11:50 PM
> To: 'PostGIS Users Discussion'
> Subject: AW: [postgis-users] Centroid Calculation Error???
> 
> 
> Martin
> 
> Here the WKT of the polygon (Swiss Coordinates)
> 
> 
> SRID=-1;POLYGON((594029.238 227076.667,594066.353 226989.68,594127.292
> 227001.806,594210.769 227017.778,594218.472 227018.871,594224.075
> 227019.225,594328.615 227028.385,594331.241 227028.382,594333.724
> 227027.428,594336.024 227026.092,594346.999 227019.388,594348.032
> 227020.432,594350.97 227023.404,594356.685 227031.13,594362.592
> 227040.194,594366.079 227045.735,594370.242 227053.048,594373.478
> 227060.511,594376.985 227068.785,594382.289 227079.941,594382.488
> 227080.884,594382.962 227087.377,594384.064 227093.667,594385.213
> 227096.506,594387.354 227100.144,594389.542 227101.84,594391.487
> 227102.947,594393.32 227104.067,594394.477 227104.395,594397.771
> 227090.279,594396.953 227091.474,594395.743 227091.446,594394.556
> 227090.976,594393.277 227089.864,594391.045 227085.427,594384.128
> 227069.284,594378.54 227057.05,594376.497 227052.679,594373.552
> 227046.879,594368.451 227038.839,594362.221 227029.185,594356.649
> 227021.43,594350.262 227013.202,594317.432 226980.488,594257.534
> 226946.253,594070.893 226878.908,593881.138 226809.861,593622.716
> 226735.129,593566.768 226904.993,593642.974 226925.582,593723.166
> 226942.676,593749.26 226939.353,593782.779 226940.175,593829.131
> 226935.872,594029.238 227076.667))
> 
> Horst
> 
> -----Ursprüngliche Nachricht-----
> Von: Martin Davis [mailto:mbdavis at VividSolutions.com]
> Gesendet am: Dienstag, 28. Oktober 2003 18:11
> An: PostGIS Users Discussion
> Betreff: RE: [postgis-users] Centroid Calculation Error???
> 
> Can you submit the WKT for the feature?  I'm curious how 
> JTS/GEOS handle
> this.
> 
> Martin Davis, Senior Technical Architect
> Vivid Solutions Inc.
> Suite #1A-2328 Government Street   Victoria, B.C.   V8T 5G5
> Phone: (250) 385 6040 - Local 308      Fax: (250) 385 6046
> 
> 
> 
> > -----Original Message-----
> > From: Düster Horst [mailto:Horst.Duester at bd.so.ch]
> > Sent: Tuesday, October 28, 2003 6:18 AM
> > To: postgis-users at postgis.refractions.net
> > Subject: [postgis-users] Centroid Calculation Error???
> > 
> > 
> > I try to calculate a centroid for a polygon with 
> >  
> > select centroid(wkb_geometry) from polygon_table;
> >  
> > You can see the result of the calculation in the attached 
> > image. The red
> > point is the place of the calculated centroid. This place 
> is obviously
> > wrong. I think the reason for this wrong placement is the 
> > weight of the
> > vertex points (yellow with black center). The centroid point 
> > is shifted to
> > the north east edge of the polygon due to the heavy 
> > concentration of vertex
> > points in this area of the polygon. In my opinion the 
> > distribution of vertex
> > points shouldn't have an influence of the centroid position.
> >  
> > Perhaps I'm wrong?? Any hints?
> >  
> > Horst
> > 
> 
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