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

[Brad Ediger]

Sounds like you're looking for ExteriorRing(polygon). A polygon has  
one exterior ring and zero or more interior rings. ExteriorRing is a  
lot cheaper (computationally) than calculating a convex hull or  
boundary.

Documentation here -> http://postgis.refractions.net/docs/ch06.html

Brad

On Feb 28, 2007, at 5:30 PM, John Carnes wrote:

> 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
>
>
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> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users

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