[postgis-users] ST_ConcaveHull

[Brian Sanjeewa Rupasinghe]

Hi,

I have a building polygon table and from the following query i get the
polygon
coordinates.

select st_astext (st_geometryn(the_geom, 1))
from building_poly;

Now what i need is to get the concave hull of all polygon coordinates.
I tried the following query but it does not work.

SELECT ST_ConcaveHull(ST_Union(select st_astext (st_geometryn(the_geom, 1))
from building_poly), 1)  As convexhull;

How to correct it?

Cheers, Sanjeewa.
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