AW: [postgis-users] Centroid Calculation Error???

Düster Horst Horst.Duester at bd.so.ch
Wed Oct 29 23:42:01 PST 2003


Martin, Paul

Thank you very much. Now my system calculates the correct centroid too.

With best regards
Horst


Dr. Horst Düster 
Leiter 
Abteilung SO!GIS Koordination
Rötihof 
4500 Solothurn 

Tel.: 032 627 25 32 
Fax: 032 627 22 14

horst.duester at bd.so.ch 
www.sogis.so.ch




-----Ursprüngliche Nachricht-----
Von: Paul Ramsey [mailto:pramsey at refractions.net]
Gesendet am: Mittwoch, 29. Oktober 2003 18:04
An: PostGIS Users Discussion
Betreff: Re: [postgis-users] Centroid Calculation Error???

The CVS version, when enabled w/ GEOS should now give the "correct" 
centroid, as per strk's email this morning.
P.

Martin Davis wrote:

> 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...
> 

>> -----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



-- 
       __
      /
      | Paul Ramsey
      | Refractions Research
      | Email: pramsey at refractions.net
      | Phone: (250) 885-0632
      \_


_______________________________________________
postgis-users mailing list
postgis-users at postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users



More information about the postgis-users mailing list