[postgis-users] Removing tiny polygons

[Hugues François]

What you say sounds very weird to me. I don't understand how postgis can consider a multipolygon as a polygon. Could you provide us a test sample of your data ?

Hugues.




-----Original Message-----
From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Tom McCallum
Sent: Tuesday, January 28, 2014 3:25 PM
To: morten at sickel.net; PostGIS Users Discussion
Subject: Re: [postgis-users] Removing tiny polygons

Yes I just want the largest polygons.  The problem being that when I simplify the polygon it appears to need a lot more simplification due to these islands rather than if it just did did one mainland polygon ( asGeoJson comes in at 437 polygons rather than 1 polygon).  Not sure why GeoJson can split it into multiple polygons but Dump[] just hands me one.

Was hoping to use ST_Area but currently cannot break down the single polygon.

Interestingly QGIS can, if I do single to multipart it can break down into main landmass and islands.  What might be an equivalent postgis method for doing this?


On Mon, 27 Jan 2014 19:15:18 -0000, Morten Sickel <morten at sickel.net>
wrote:

> It depends on what you mean with "remove" - do you want to just have 
> the large polygons without the area that is covered by the small ones 
> or do you want to add the area of the small polygons onto one or more 
> of the larges? (e.g. how one typically wants to handle shiver 
> polygons)
>
> In the first case it is as easy as a query like
>
> select the_geom where ST_area(the_geom) > ...
>
> Morten
>
>
> Tom McCallum skrev:
>> Hi all,
>>
>> If I have a polygon geometry field which seems to be made up of a 
>> large number of tiny polygons and some larger ones, what is the best 
>> way to remove polygons below a certain size?  Would I need to 
>> preprocess this and save in a new table/record or can I dynamically 
>> do it?
>>
>> Thanks
>>
>> Tom
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