[postgis-users] geos result sets

[Martin Davis]

I thought I better leap to the defence of JTS/GEOS.  I've analyzed the
situation and (no surprise to me) found that the results from GEOS are
correct.  The Within=FALSE result is caused by a slight difference in
the vertices in the two coverages. 

I've attached a full analysis (with screenshots from JUMP).

I have no idea why ArcView gives a different result - you'll have to ask
ESRI    8^)

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: James S reid [mailto:james.reid at ed.ac.uk] 
> Sent: Wednesday, February 25, 2004 1:09 AM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] geos result sets
> 
> 
> hi  - thanks and I appreciate that your times at a premium - 
> Ive checked that the geoms are valid and run the follwing sql 
> (2 tables 1=large poly,1=small polys (8 polys):
> 
> test=# select small.* into temp from small,large where
> within(small.the_geom,large.the_geom) = TRUE;
> 
> dumping temp gives sthe GEOS result set seen in the 
> screenshot attached (along with the sql load files for the 
> original shapes).
> 
> as you can see - AV gets all eight polys and GEOS only the seven?
> 
> Im I missing something or is there a bug?
> 
> cheers
> 
> james
> 
> ----- Original Message ----- 
> From: "David Blasby" <dblasby at refractions.net>
> To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
> Sent: Tuesday, February 24, 2004 5:48 PM
> Subject: Re: [postgis-users] geos result sets
> 
> 
> > Why dont you send us the actual query thats going wrong?
> >
> > ie. something like:
> >
> > select within(<polygon 1>,<polygon 2>);
> >
> > I need to see what <polygon 1> and <polygon 2> are to do 
> any testing. 
> > Saying GEOS and ARC have a different answer isnt enough to 
> diagnose a 
> > problem - I need a specific example.
> >
> > I, unfortunately, dont have time to sift through your data 
> in PostGIS 
> > and ARC to find differences.
> >
> > Did you check to see if your geometries are valid (ie. select
> > isvalid(the_geom) from <table>;)?
> >
> > dave
> > _______________________________________________
> > postgis-users mailing list postgis-users at postgis.refractions.net
> > http://postgis.refractions.net/mailman/listinfo/postgis-users
> 
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