[postgis-users] working with multipolygons

[Simon Greener]

Andy,

Is this of any use to you:

http://www.spatialdbadvisor.com/postgis_tips_tricks/92/filtering-rings-in-polygon-postgis

regards
Simon
On Sat, 09 Oct 2010 08:11:24 +1100, lplateandy <andy at centremaps.co.uk> wrote:

>
> Hi,
>
> Looking for some tips about the right direction to take when tidying up some
> multi-polygon data. I
> have lots of 2 by 2 kilometre chunks defining a type of coverage.
>
> The information for each 2 by 2km chunk has been merged into multi-polygons,
> it may have holes as small as 25 by 25 metres or equally the area may only
> be partly filled along with little 25 by 25 metre islands.
>
> Is there a method to delete parts of a multi-polygon for example:
>
> 1) Any elements which represent a hole
> 2) Any elements below a certain threshold size
>
> I can imagine that dissolving the multi-polygon would allow me to apply
> changes to the islands but am not sure about the holes
>
>
> I also found that when i tried to carry out some queries such as
> ST_SimplifyPreserveTopology or ST_Envelope i get null areas or bounding
> boxes of just one of the holes - as though the action is just being applied
> to one of the elements in the polygon - perhaps the first one - is that the
> case?
>
>
> Any pointers to get me started would be much appreciated.
>
> Thanks in advance
>
> Andy


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