[postgis-users] Feautures omitted from ST_Buffer operation

[Roger André]

Thanks for filing the bug.  It's definitely something bad, I did a test
where I buffered every country in the world and then underlaid the original
shapefile in solid red.  There are alot of random places showing though.
The explode, buffer, union and re-assemble process seems to give correct
results though.

Thanks again for the follow-up.
--

On Thu, Mar 26, 2009 at 11:02 AM, Martin Davis <mbdavis at refractions.net>wrote:

> Thanks for that.  Nice test case!  FWIW, this runs fine in JTS.  Hopefully
> someone on the GEOS side can take a look at this.
>
> Roger André wrote:
>
>> Ok, here is the WKB.  Let me know if there are any problems with the file.
>> --
>>
>> On Thu, Mar 26, 2009 at 8:57 AM, Martin Davis <mbdavis at refractions.net<mailto:
>> mbdavis at refractions.net>> wrote:
>>
>>    I don't think this can be the problem - a buffer of a linestring
>>    should still produce a polygon.
>>
>>    This is probably a bug in the GEOS buffer algorithm.  It would
>>    help if you posted the WKB or WKB for the geometry.
>>
>>
>>    Chris Hermansen wrote:
>>
>>        This sounds to me like you might be buffering a linestring and
>>        not a
>>        polygon.  Is that possible?  Ie are the countries represented as
>>        outlines (linestrings) rather than polygons?
>>
>>        Roger André wrote:
>>
>>            Hi All,
>>
>>            I'm having some problems with features that are being
>>            returned from an
>>            ST_Buffer operation in PostGIS.  When I try to buffer the
>>            extents of
>>            Papua New Guinea, a large region in the middle of its
>>            extents is
>>            omitted.  You can see a visual representation of this at
>>
>> http://lagerratrobe.blogspot.com/2009/03/problem-with-postgis-stbuffer.html
>>
>>            If I just select the country itself, I get back all of the
>>            features
>>            that I'm expecting.  In the image I've posted above, the
>>            black area
>>            indicates the results of that query.
>>
>>            I am using postgresql-8.3.5, and postgis-1.3.3.  My select
>>            statements
>>            is as follows:
>>               select name, Buffer(the_geom, .12) from coastlines where
>>            iso_3_code = 'PNG';
>>
>>            I've tried this using both a free countries shapefile, as
>>            well as an
>>            ESRI one, and get the same results.  I'm a bit baffled,
>>            and unsure if
>>            I have a problem with both data sets, or in my query,
>>            or...?  If
>>            someone else has had a similar problem in the past, and
>>            can shed some
>>            light on it, I'd greatly appreciate it.
>>
>>            Thanks in advance,
>>
>>            Roger
>>            --
>>
>>  ------------------------------------------------------------------------
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>>
>>
>>
>>
>>    --    Martin Davis
>>    Senior Technical Architect
>>    Refractions Research, Inc.
>>    (250) 383-3022
>>
>>
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>
> --
> Martin Davis
> Senior Technical Architect
> Refractions Research, Inc.
> (250) 383-3022
>
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