blowing up on negative value buffer() call

[Leo Shklovskii]

Hi Geos-Devel,

I'm using GeoDjango (which wraps GEOS) to manipulate some polygons
representing states, cities & counties.

We simplify many of the polygons in our original census dataset and as a
result, some of them overlap (when they didn't originally). Because of
this, I need to reduce some of them in size before I run queries on them
to prevent wrong results from 'intersects' queries.

The first thing I tried seems to work fairly well:

location.mpoly.buffer(-.01).buffer(0)

Ideally, the first call shrinks the poly and the second one makes sure
that its valid.

Unfortunately, I've found several polygons that are valid but cause the
first call to buffer() to blow up (memory leak + spiked cpu + doesn't
return).

Should I file this as a GEOS bug? or am I not using buffer() correctly?

If the latter, what would be a better way to shrink a polygon?

Thanks in advance for your time!

--
--Leo
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[strk]

On Fri, Oct 30, 2009 at 02:23:17PM -0700, Leo Shklovskii wrote:

> Unfortunately, I've found several polygons that are valid but cause the
> first call to buffer() to blow up (memory leak + spiked cpu + doesn't
> return).
>
> Should I file this as a GEOS bug? or am I not using buffer() correctly?

Negative buffer is supported, so looks like a bug.
The best report would be in the form of an XML test.
See tests/xmltester/tests/TestBufferExternal2.xml
for examples on how to format a testcase for negative buffers.

Or feel free to just report your input polygon WKT.

--strk;

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