[postgis-users] Getting boundary of set of polygons

[Hugues François]

Hello,

On my side, I often use st_buildarea(st_exteriorring((st_dump(geom)).geom)). And if I want to keep a single object for the original one, I union or collect them regarding their gid.

HTH

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: Monday, January 27, 2014 1:51 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Getting boundary of set of polygons

St_MakePolygon does not take a multilinestring.
ST_BuildArea looked possible, but it gives me back lots of little areas and not a single boundary for the whole set.

It looks as though ST_Dump with ST_MakePolygon may be useful but am still trying to get the right form something like

ST_MakePolygon( ST_DUMP( ST_BOUNDARY( ST_COLLECT( wkb_boundary ) ) .geom )

But it does not like the .geom bit.

Any suggestions?

On Mon, 27 Jan 2014 12:35:51 -0000, Nicolas Ribot <nicolas.ribot at gmail.com> wrote:

> Hi,
>
> You should try st_makePolygon, or st_buildArea depending on the result 
> you want (keeping holes or removing them).
>
> Nicolas
>
>
>
> On 27 January 2014 13:32, Tom McCallum <termcc at googlemail.com> wrote:
>
>> Hello all,
>>
>> I am trying to get the boundary of a geometry(polygon) field in 
>> postgis (multiple polygons in this field).  I have this so far:
>>
>> ST_BOUNDARY(ST_COLLECT(wkb_geometry))
>>
>> which outputs MultilineString.  I need to convert this to a polygon.  
>> I have tried all sorts of things from ST_DUMP to converting to text 
>> and then trying ST_BdPolyFromText but got nothing to work so far.  
>> ST_Convexhull gives me a polygon but unfortunately its not what I 
>> want.
>>
>> Could someone let me know what I should be calling.
>>
>> Thanks
>>
>> Tom
>> _______________________________________________
>> postgis-users mailing list
>> postgis-users at lists.osgeo.org
>> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
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