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<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2>Erik,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2>I think the ST_Difference function may work for
you.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2>Basically get the extent of your world make a polygon out
of it and then subtract the world</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2>So something like the below</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2>SELECT ST_Difference(ST_SetSRID(ST_Extent(the_world),
ST_SRID(the_world), the_world)</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2>Hope that helps,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><FONT face=Arial
color=#0000ff size=2>Regina</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=220391913-07082008><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>erik<BR><B>Sent:</B> Thursday, August 07, 2008 9:11 AM<BR><B>To:</B> PostGIS
Users Discussion<BR><B>Subject:</B> [postgis-users] creating a
mask<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=ltr>Hello, <BR><BR>I don't know if the terminology I use is correct but
I would like to create a mask of layer I have.<BR>For example, from the shape of
the world I would like to keep only the oceans, the negative of the initial
shape.<BR>I haven't found any info or documentation about this. Can this be done
in PostGIS?<BR><BR>Many thanks!<BR><BR>Erik<BR></DIV></BODY></HTML>
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