[Mapserver-users] GEOS intersection problem

[Mark Cave-Ayland]

Hi Zhigang,

It would seem that this is not a mapserver issue but most likely a
PostGIS/GEOS issue. I would suggest reposting this to the geos-devel
mailing list (see http://geos.refractions.net) and the postgis-users
mailing list (see http://postgis.refractions.net).


Kind regards,

Mark.

---

Mark Cave-Ayland
Webbased Ltd.
Tamar Science Park
Derriford
Plymouth
PL6 8BX
England

Tel: +44 (0)1752 764445
Fax: +44 (0)1752 764446


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> -----Original Message-----
> From: mapserver-users-admin at lists.gis.umn.edu 
> [mailto:mapserver-users-admin at lists.gis.umn.edu] On Behalf Of 
> songzh at cs.orst.edu
> Sent: 08 June 2004 05:40
> To: mapserver-users at lists.gis.umn.edu
> Subject: [Mapserver-users] GEOS intersection problem
> 
> 
> 
> When I performed the intersection between a MULTILINESTRING 
> and a POLYGON, the generated MULTILINESTRING shot off a line 
> which went outside the images
> extents. The details are as the following:   
> 
>   1) The version of GEOS is downloaded from: 
> [2003//11/06]geos-1.0.0.tar.gz on http://geos.refraction.net
>      It's the latest version I can find. 
>   2) The intersection geometry objects are as the following. 
> 
> geom_base (it has three single lines with a common jointed point): 
>   "SRID=6010;MULTILINESTRING((602797 1045929,602897 
> 1045629),(602897 1045629,602997 1045929),(602897 
> 1045629,602897 1045529,602897 1045599,602897 1045439,602897 1045429))"
> 
> geom_py (a rectangle):
>   "SRID=6010;POLYGON((602797 1045829,602997 1045829,602997 
> 1045529,602797 1045529,602797 1045829))"
> 
>   3) After the SQL statement "select intersection(geom_base, 
> geom_py) from intersect_test" was issued, the intersected 
> geometry object was:
> 
> geom_intersect ( a multilinestring):
>   "SRID=6010;MULTILINESTRING((602830.333333333 1045829,602897 
> 1045629),(602897 1045629,602963.666666667 1045829),(602897 
> 1045629,602897 1045599),(602897 1045599,2.30261934254173e-269 
> 1.20137436645991e-301))"
>      
> 
> We can see that one of the generated multiline string has a 
> point " 2.30261934254173e-269 1.20137436645991e-301 " which 
> is actually (0,0). It shows that one of the result line 
> string links to the point (0, 0), which caused the line going 
> out the image range. I want to know if anybody has any idea 
> about this. How to avoid it?
> 
> Thanks a lot!
> 
> 
> Yours,
> Zhigang Song
> 
> 
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