[postgis-users] Boundary() without the internal holes?

[John Carnes]

I am trying to figure out how to get a polygon that is the boundary  
of a geounion of polygons without getting polygons for the internal  
holes.

The boundary() function is close, but includes the internal holes.

     SELECT boundary(geomunion(p.the_geom)) FROM parcels AS p WHERE  
p.neighborhood=5;

A convex hull, leaves out the internal holes, but the resulting  
polygon doesn't touch the actual boundary anywhere that it is concave.

Thanks in advance for your ideas on how to do this.
I'd really like to avoid having to delete the internal hole polygons  
by hand, which is my current solution.

John Carnes
MapTools