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<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2>Bob,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2>Not quite clear what you are looking for
here.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2>So are you trying to put your text identifier on a hole in
a geometry? What if there is no hole?</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2>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.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2>To get the centroid of a hole, I think you need to turn it
into non-hole (like turning anti-matter into matter).</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2>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</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=916404318-28032009><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
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<FONT face=Tahoma size=2><B>From:</B>
postgis-users-bounces@postgis.refractions.net
[mailto:postgis-users-bounces@postgis.refractions.net] <B>On Behalf Of </B>Bob
Pawley<BR><B>Sent:</B> Saturday, March 28, 2009 11:24 PM<BR><B>To:</B> PostGIS
Users Discussion<BR><B>Subject:</B> [postgis-users] Finding Empty
Space<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV><FONT face=Arial size=2>
<DIV><FONT face=Arial size=2>Hi</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The expression st_isempty returns
a boolean set.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Is there any method of returning the centroid
coordinates of an empty space wihtin a given geometry?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I want to add a text identifier to a geometry
without it being lost in the clutter.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Bob</FONT></DIV></FONT></DIV></BODY></HTML>