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

[Paul Ramsey]

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
> 
> 
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> Mapserver-users at lists.gis.umn.edu
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