[postgis-users] ST_Collect

[Carsten Hogertz]

Hey that's perfect.
The only thing when I use the array_agg is that I normaly get this:

"{"Moth Theatre Company"}"

but in some cases I get this:

"{"Sacred Fools Theater Company","Sacred Fools Theater Company","Sacred
Fools Theater Company"}"

Any idea why this happens?
Thanks
Carsten


2013/10/11 Nicolas Ribot <nicolas.ribot at gmail.com>

> Hi,
>
> you could store initial information in a array of values of
> desc_string or other attribute, using array_agg function (or create a
> concatenated string using string_agg function):
>
> ...
> SELECT a.poi_id,
>     a.geom,
>     array_agg(desc_string) as descs,
>     St_collect(b.geom) AS b_geom
>
>
> Nicolas
>
>
> On 11 October 2013 13:16, Carsten Hogertz <carsten.hogertz at gmail.com>
> wrote:
> > Thanks Hugues,
> > you helped alot. I added some text to your SQL like the following:
> >
> > WITH myselect
> >
> >     AS (SELECT a.poi_id,
> >
> >     a.geom,
> >
> >     St_collect(b.geom) AS b_geom
> >
> > FROM
> >
> >     ciss_poi a, ciss_poi b
> >
> > WHERE
> >
> >     St_dwithin(a.geom, b.geom, ( 0.5 / 111.111 ))
> >
> >     AND a.poi_id != b.poi_id
> >
> >     AND a.desc_string = b.desc_string
> >
> > GROUP BY
> >
> >     a.poi_id, a.geom)
> >
> > SELECT ROW_NUMBER() over (order by geom) as id,
> >
> >     St_centroid(St_convexhull(St_collect(geom, b_geom))) as geom
> >
> > FROM
> >
> >     myselect m
> >
> >
> > With this statement I get the centroid of the grouped point's convex
> hulls.
> > Obviously only the geography.
> >
> > What can I do to label the information of one of the "initial" points
> that
> > formed the convex hull to the new centroid?
> >
> >
> > Best Regards and thank you very much
> >
> > --
> >
> > Carsten
> >
> >
> >
> >
> >
> >
> > 2013/10/11 Hugues François <hugues.francois at irstea.fr>
> >>
> >> I think the problem is a bit more complicated. The self join is the good
> >> approach but you can't collect the boolean output of st_dwithin. I
> should
> >> have tried something like
> >>
> >> with myselect as (
> >>     select a.id, a.geom, st_collect(b.geom) as b_geom from mytable a,
> >> mytable b
> >>     where st_dwithin(a.geom, b.geom, 500)
> >>     and a.id != b.id
> >>     group by a.id, a.geom
> >>     )
> >>
> >> select a.id, st_collect(geom, b_geom) from myselect
> >>
> >> Hugues.
> >>
> >> ________________________________
> >> From: postgis-users-bounces at lists.osgeo.org
> >> [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Carsten
> Hogertz
> >> Sent: Friday, October 11, 2013 9:30 AM
> >> To: PostGIS Users Discussion
> >> Subject: [postgis-users] ST_Collect
> >>
> >> Hello,
> >>
> >> I've got a question about using ST_Collect.
> >>
> >> I have one table with hundrets of thousands of points. Within this
> table I
> >> want to collect the points that are within a 500 meter radius and
> calculate
> >> a convex hull around them.
> >>
> >> Since the ST_DWithin needs (geom, geom, distance) and I only have one
> >> table with points, do I first have to perform a self join to identify
> the
> >> points within 500 meters and then a ST_Collect to group these points?
> Or can
> >> I somehow do it without joining the one table with itself?
> >>
> >> And can I use the ST_DWithin inside the ST_Collect? Like
> >> ST_Collect(ST_DWithing(geom,geom,distance))?
> >>
> >> Thanks for your help!
> >> --
> >> Carsten
> >>
> >> _______________________________________________
> >> postgis-users mailing list
> >> postgis-users at lists.osgeo.org
> >> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
> >
> >
> >
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