[geos-devel] Re: [Mapserver-users] GEOS: buffer function for MULTIPOLYGON geometry object

[Martin Davis]

Actually in OGC the components of a MultiPolygon can touch at single
points, so this can't be ruled out as invalid a priori.

However - submitters, you should ALWAYS include the WKT for the geometry
inputs with questions of this kind.  Otherwise there's no way to debug
the problem.

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: Paul Ramsey [mailto:pramsey at refractions.net] 
> Sent: April 29, 2004 2:52 PM
> To: songzh at cs.orst.edu
> Cc: GEOS Development List
> Subject: [geos-devel] Re: [Mapserver-users] GEOS: buffer 
> function for MULTIPOLYGON geometry object
> 
> 
> What is isvalid() return for your geometry? True or false? A 
> multipolygon as you describe sounds suspiciously like an 
> invalid shape.
> 
> songzh at cs.orst.edu wrote:
> 
> > Hello list:
> > 
> >   I recently tested GEOS 'buffer(MULTIPOLYGON_geo_column, 100)' 
> > function and found something strange:
> >   1) I manually created a MULTIPOLYGON object which is shown as two 
> > trangles connected by one point.
> >   2) then I issued command as:
> > "update motelsites set buffer_py=buffer(the_geom_py,500) 
> where gid=36;" 
> >   3) The strange thing is: only the left triangle has been 
> buffered and the
> > buffer area has been shown around this triangle. The right 
> triangle didn't show
> > up its buffered area at all.
> > 
> >   Did I do anything wrong or there is some problem with the GEOS's 
> > buffer function to deal with MULTIPOLYGON object ?
> >   Thanks for any advice!
> > 
> > 
> > Zhigang Song
> > 
> > 
> > _______________________________________________
> > Mapserver-users mailing list Mapserver-users at lists.gis.umn.edu
> > http://lists.gis.umn.edu/mailman/listinfo/mapserver-users
> 
> 
> -- 
>        __
>       /
>       | Paul Ramsey
>       | Refractions Research
>       | Email: pramsey at refractions.net
>       | Phone: (250) 885-0632
>       \_
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