[postgis-users] Finding Empty Space

Paragon Corporation lr at pcorp.us
Sat Mar 28 11:48:31 PDT 2009

Not quite clear what you are looking for here.
So are you trying to put your text identifier on a hole in a geometry?  What
if there is no hole?
Also the centroid of a geometry is not guaranteed to lie on the geometry so
even if you turned empty space into non-empty so you can take the centroid
of it, the centroid may not be in the hole.
To get the centroid of a hole, I think you need to turn it into non-hole
(like turning anti-matter into matter).
you can do this by say taking the exterior of the covering area, and then
using ST_Difference.  The result would be the holes turned into geometries


From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
Sent: Saturday, March 28, 2009 11:24 PM
To: PostGIS Users Discussion
Subject: [postgis-users] Finding Empty Space

The expression st_isempty returns a boolean set.
Is there any method of returning the centroid coordinates of an empty space
wihtin a given geometry?
I want to add a text identifier to a geometry without it being lost in the
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