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

[René Fournier]

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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