select st_isvalid(wkb_geometry) from mytable
NOTICE: Ring Self-intersection at or near point 4173.162435251591
6968968.0578562981
st_isvalid
------------
f
(1 row)
It had 287 interior rings. So am searching now for the largest. Thanks
would not have found this without your help!
On Tue, 28 Jan 2014 15:46:21 -0000, Rémi Cura <[email protected]> wrote:
If you are saying that dump doesn't break your multi polygon into pieces,
either
_ dump has a bug (unlikely)
_ you don't have a multipolygon but a geometry collection (try
ST_Dump(ST_CollectionExtract(geom,2)))
_you have an invalid simple polygon (try st_isvalid() )
_you have a simple polygon where interior rings should be stand alone
polygon, use St_ringextract
Cheers,
Rémi-C
2014-01-28 Hugues François <[email protected]>
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: [email protected] [mailto:
[email protected]] On Behalf Of Tom McCallum
Sent: Tuesday, January 28, 2014 3:25 PM
To: [email protected]; 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 <[email protected]>
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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>>
>
>
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