I'm not a Windows user these days and unable able to reproduce your issue, but I'll help you as much as I can and try to pull the Windows packager into the discussion.
Is it only to_wkt() that produces an access violation? Are you able to evaluate the area? Could it be the sheer size of the output? Your WKT string could be around 1 GB: 6 million squares x 4 corners x 50 bytes per corner (approx). Howard Butler just pointed out to me that the GEOS (the C lib under Shapely) isn't checking whether allocation of memory for the WKT value succeeds. If you're low on memory, it might fail without notice and leave a null pointer. On Sun, Aug 8, 2010 at 7:18 PM, Darren Waters <[email protected]> wrote: > Hi Sean, > > Thanks for your reply. My version of Shapely came from the link on > http://trac.gispython.org/lab/wiki/Shapely. My version of python is 2.5.2 > and was from python.org. Also, when I referred to a large set of point > data, I am talking of the order of 6 million points that I am performing the > cascaded union on. > > Thanks in advance for any advice that you can give me. > > Cheers > Darren > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Sean Gillies > Sent: Saturday, 7 August 2010 1:35 PM > To: gispython.org community projects > Subject: Re: [Community] Access Violation Error when using to_wkt method > > On Wed, Aug 4, 2010 at 12:02 AM, Darren Waters > <[email protected]> wrote: >> Hi All, >> >> I am using shapely 1.2.2 (python 2.5 on a Windows system) to generate >> a coverage polygon for a large set of point data. To achieve this I >> am producing a series of square polygons (buffered around each point) >> and then using a cascaded_union to join overlapping geometries to >> yield a multipolygon object. Unfortunately, when I try and output this >> geometry to a well known text representation, using the to_wkt() >> method, I get an error >> (*** WindowsError: exception: access violation reading 0x00000000). >> Has anyone else experienced this problem and can anyone suggest a > solution. >> This problem seems like it may be related to an issue discussed on the >> geos-devel list >> (http://www.mail-archive.com/[email protected]/msg00996.html) >> >> Thanks >> Darren > > Hi Darren, > > Aron's patch has been in Shapely for some time. Where did your Windows > Python come from? Python.org? Elsewhere? > -- Sean _______________________________________________ Community mailing list [email protected] http://lists.gispython.org/mailman/listinfo/community
