[postgis-users] Creating a simple polygon encompassing a given number of points

[Nicolas Ribot]

Hi,

I think you could cast geography to geometry to collect, then cast
back to geography to store ?



On 12 September 2012 17:42, René Fournier <m5 at renefournier.com> wrote:
> Yes, this works great.
>
> UPDATE territories SET border = (SELECT
> ST_ConvexHull(ST_Collect(ST_GeomFromText('MULTIPOINT(-111.868842 50.569455,
> -111.898634 50.569992, -111.907919 50.583764, -111.868859 50.569452)') ) ))
> WHERE id = 3014;
>
>
> Now... I'm trying to figure out, how to do the same, except create the
> border (polygon) from points in another table, e.g.:
>
> UPDATE territories SET border = (SELECT ST_ConvexHull(ST_Collect( SELECT
> location FROM addresses WHERE territory_id = 3014 ))) WHERE id = 3014;
>
> ...returns "ERROR:  function st_collect(geography) does not exist HINT:  No
> function matches the given name and argument types. You might need to add
> explicit type casts."
>
> So I'm wondering, since both border (final polygon) and location (source of
> points) are of type geography, what's the best way to go about this? Or
> should I have just used geometry types? Sorry for the dumb questions, I'm
> trying to define the schemas by best practices so I don't have to fix them
> later. Geography seemed right when I started the project.
>
>
>
> On 2012-09-11, at 1:18 AM, Paolo Corti wrote:
>
> On Tue, Sep 11, 2012 at 3:44 AM, René Fournier <m5 at renefournier.com> wrote:
>
> Thanks Nicolas,
>
>
> UPDATE territories SET border =
>
> ST_ConvexHull(ST_Collect(ST_GeomFromText('MULTIPOINT(50.569455 -111.868842,
>
> 50.569992 -111.898634, 50.583764 -111.907919, 50.569452 -111.868859)') ) )
>
> WHERE id = 3014;
>
> ERROR:  cannot use aggregate function in UPDATE
>
> LINE 1: UPDATE territories SET border = ST_ConvexHull(ST_Collect(ST_...
>
>
>
> Using a sub-select should work:
>
> UPDATE territories SET border = (SELECT
> ST_ConvexHull(ST_Collect(ST_GeomFromText('MULTIPOINT(50.569455
> -111.868842, 50.569992 -111.898634, 50.583764 -111.907919, 50.569452
> -111.868859)') ) ))
> WHERE id = 3014;
>
> regards
> p
>
> --
> Paolo Corti
> Geospatial software developer
> web: http://www.paolocorti.net
> twitter: @capooti
> skype: capooti
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