[postgis-users] Feautures omitted from ST_Buffer operation

[Roger André]

Ok, here is a way to do it, but it seems a bit ridiculous to have to do a
2-part operation like this:

SELECT c.name, geomunion(the_geom) FROM
    (SELECT name, ST_Buffer((ST_Dump(the_geom)).geom, .12) AS the_geom FROM
coastlines) c
WHERE c.name LIKE 'Papua%' GROUP BY c.name;
--

On Wed, Mar 25, 2009 at 9:09 PM, Roger André <randre at gmail.com> wrote:

> Hi Chris,
>
> I don't think it's a linestring.  I checked the sql load file I made, and
> the table is defined in it as a MULTIPOLYGON:
>
> SELECT AddGeometryColumn('','coastlines','the_geom','-1','MULTIPOLYGON',2);
>
> Not really sure how else to test though.
> --
>
>
>
> On Wed, Mar 25, 2009 at 8:46 PM, Chris Hermansen <
> chris.hermansen at timberline.ca> 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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>> >
>>
>>
>> --
>> Regards,
>>
>> Chris Hermansen         mailto:chris.hermansen at timberline.ca
>> tel+1.604.714.2878 · fax+1.604.733.0631 · mob+1.778.232.0644
>> Timberline Natural Resource Group · http://www.timberline.ca
>> 401 · 958 West 8th Avenue  · Vancouver BC · Canada · V5Z 1E5
>>
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