I kind of gave up on that, it seemed to work better just sending straight
through simplify (my objective was to reduce the load time). Everytime I
tried one of the suggestions I ended up with one tiny polygon and none of
the others seemed to be represented. I think the underlying geometry must
have been different to what I thought it was.
On Mon, 27 Jan 2014 16:54:21 -0000, Hugues François
<[email protected]> wrote:
I hope you'll tell us your final choice ! In your last query you need
to add a pair of bracket to get only geometries from dump. Syntax is :
(st_dump(geom)).geom.
Hug
Tom McCallum <[email protected]> a écrit :
Thanks for all your replies, not quite there but got some ideas.
On Mon, 27 Jan 2014 13:51:26 -0000, Rémi Cura <[email protected]>
wrote:
You could use convex or concav envelop.
You can also union the geometries (eventually simplifying by neg buffer
then pos buffer)
That's if you want precise boundary.
If you just need bbox ...
Cheers,
Rémi-C
2014-01-27 Hugues François <[email protected]>
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: [email protected] [mailto:
[email protected]] 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
<[email protected]>
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 <[email protected]> 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
>> [email protected]
>> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
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