[postgis-users] Removing tiny polygons

[Tom McCallum]

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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