[postgis-users] Getting boundary of set of polygons

[Tom McCallum]

Hello all,

I am trying to get the boundary of a geometry(polygon) field in postgis  
(multiple polygons in this field).  I have this so far:

ST_BOUNDARY(ST_COLLECT(wkb_geometry))

which outputs MultilineString.  I need to convert this to a polygon.  I  
have tried all sorts of things from ST_DUMP to converting to text and then  
trying ST_BdPolyFromText but got nothing to work so far.  ST_Convexhull  
gives me a polygon but unfortunately its not what I want.

Could someone let me know what I should be calling.

Thanks

Tom