[postgis-users] Buffering a convexhull

[Nicolas Ribot]

> I used the following query to make a buffer of 1m iutward to a convexull
> created by union of a set of polygons. But it gives an error.Why?
> SELECT ST_As_Text(ST_Buffer (foo.the_geom, 1)) from (select
> (ST_ConvexHull(ST_Union(the_geom))) from building_poly) As foo;

Hi Sanjjewa,

The function is st_astext, not st_as_text.

Furthermore, you are calling foo.the_geom in the outer query though
the column in the inner query is not called 'the_geom'.
Is this works better with an alias on the convexHull operation ?:

SELECT ST_AsText(ST_Buffer (foo.the_geom, 1))
from (
    select ST_ConvexHull(ST_Union(the_geom)) as the_geom
    from building_poly
) As foo;

Nicolas