[Community] buffer problem

[Sean Gillies]

Jaakko Salli has been making GEOS DLLs for the Shapely windows  
installers. I'll see if he's able to make an updated one.

Sean

On Aug 3, 2009, at 12:12 PM, Daniel O'donohue wrote:

> hi my search for libgeos showed that I have three versions on my  
> machine
> libgeos-3-0-0.dll is the only one included in the python path
> the other two versions are
> libgeos-2.dll and libgeos_c-1.dll which are part of Quantum GIS
>
> any ideas as to how I can get a hold of libgoes-3-0-0-1??
>
> bearing in mind I an using shapely-1.0.12
>
>
> thanks
>
> dan
>
> > From: sean.gillies at gmail.com
> > To: community at lists.gispython.org
> > Date: Fri, 31 Jul 2009 09:54:12 +0200
> > Subject: Re: [Community] buffer problem
> >
> > Search for libgeos SO or DLL files on your system. If you're using  
> an
> > older version like 2.2.3, it's very possible that you've found a  
> GEOS
> > bug.
> >
> > Sean
> >
> > On Jul 30, 2009, at 5:06 PM, Daniel O'donohue wrote:
> >
> > > I'm not sure how to find out what version of GEOS I'm using
> > > but I have deleted the shapely module and reinstalled it using the
> > > latest
> > > version.
> > > after that I also run a copy of your code
> > >
> > > from shapely.geometry import MultiPoint
> > > polya = MultiPoint([(-1.0, -2.0), (1.0, -2.0), (-1.0, 2.0),
> > > (1.0,2.0)]).convex_hull
> > > polyb = MultiPoint([(-1.0, -2.0), (1.0, -2.0), (-1.0, 2.0),
> > > (1.0,2.0)]).convex_hull
> > > buffa = polya.buffer(1.0)
> > > buffb = polya.buffer(1.0)
> > >
> > > print buffa.contains(polya)
> > >
> > > print buffb.contains(polya)
> > >
> > > print buffb.contains(polyb)
> > >
> > > print buffa.contains(polyb)
> > >
> > > print polya.equals(polyb)
> > >
> > > which produces the following
> > >
> > > False
> > > False
> > > False
> > > False
> > > True
> > >
> > > I'm stuck
> > >
> > > cheers
> > > dan
> > >
> > >
> > > > From: sean.gillies at gmail.com
> > > > To: community at lists.gispython.org
> > > > Date: Thu, 30 Jul 2009 14:11:11 +0200
> > > > Subject: Re: [Community] buffer problem
> > > >
> > > > On Jul 28, 2009, at 8:55 PM, Daniel O'donohue wrote:
> > > >
> > > > > hi there
> > > > >
> > > > > I'm am trying to use the following algorthyim to test to see  
> if
> > > two
> > > > > geometries match
> > > > >
> > > > > Geometry A matches geometry B if
> > > > > A is contained in buffer(B, d)
> > > > > and B is contained in buffer(A, d)
> > > > > and boundary(A) is contained in buffer(boundary(B), d)
> > > > > and boundary(B) is contained in buffer(boundary(A), d)
> > > > >
> > > > >
> > > > >
> > > > > polya = MultiPoint([(-1.0, -2.0), (1.0, -2.0), (-1.0, 2.0),  
> (1.0,
> > > > > 2.0)]).convex_hull
> > > > > polyb = MultiPoint([(-1.0, -2.0), (1.0, -2.0), (-1.0, 2.0),  
> (1.0,
> > > > > 2.0)]).convex_hull
> > > > >
> > > > > buffa = polya.buffer(1.0)
> > > > > buffb = polya.buffer(1.0)
> > > > >
> > > > > polya_bound = polya.boundary
> > > > > polyb_bound = polyb.boundary
> > > > >
> > > > >
> > > > > print buffa.contains(polyb)
> > > > > print buffb.contains(polya)
> > > > > print buffa.contains(polyb_bound)
> > > > > print buffb.contains(polya_bound)
> > > > >
> > > > >
> > > > > I use a convex hull to ensure that the polygon created is only
> > > > > considering the outside points
> > > > > and my points are not ordered so this ensures that I valid  
> polygon
> > > > > is returned
> > > > >
> > > > > How ever the last four print statments return
> > > > >
> > > > > False
> > > > > False
> > > > > True
> > > > > True
> > > > >
> > > > > both geometries are identical so why would the buffer of one  
> not
> > > > > contain the either one of the
> > > > > original geometires??
> > > > >
> > > > > I am really studk here and would be greatfull for any help
> > > > >
> > > > > cheers
> > > > >
> > > > > dan
> > > >
> > > > Hi Dan,
> > > >
> > > > I can't reproduce this problem. Here's what I get, using Shapely
> > > > 1.0.12 and GEOS 3.1.0:
> > > >
> > > > >>> from shapely.geometry import MultiPoint
> > > > >>> polya = MultiPoint([(-1.0, -2.0), (1.0, -2.0), (-1.0, 2.0),
> > > (1.0,
> > > > 2.0)]).convex_hull
> > > > >>> polyb = MultiPoint([(-1.0, -2.0), (1.0, -2.0), (-1.0, 2.0),
> > > (1.0,
> > > > 2.0)]).convex_hull
> > > > >>> buffa = polya.buffer(1.0)
> > > > >>> buffb = polya.buffer(1.0)
> > > > >>> buffa.contains(polya)
> > > > True
> > > > >>> buffb.contains(polya)
> > > > True
> > > > >>> buffb.contains(polyb)
> > > > True
> > > > >>> buffa.contains(polyb)
> > > > True
> > > > >>> polya.equals(polyb)
> > > > True
> > > >
> > > > What's your GEOS version?
> > > >
> > > > Sean
> > > >
> > > > _______________________________________________
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> > --
> > Sean Gillies
> > Programmer
> > Institute for the Study of the Ancient World
> > New York University
> >
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--
Sean Gillies
Programmer
Institute for the Study of the Ancient World
New York University