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<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2>Why wouldn't you use a nearest neighbor calculation
as demonstrated here (using DISTINCT ON)?</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2><A
href="http://postgis.refractions.net/documentation/manual-svn/ST_DWithin.html">http://postgis.refractions.net/documentation/manual-svn/ST_DWithin.html</A></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2>Keep in mind ST_DWithin and ST_Distance don't care
about whether a geometry is a line or polygon or point or collection or
whatever. They will always consider the minimum distance between 2
geometries.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2>ST_DWithin will use a spatial index where as ST_Distance
will not. So for ST_DWithin to work, you have to make the
assumption,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2>the closest road to any point is no more than X units
away. The bigger you make the X, the less efficient the index search, but
the less likely you will leave a point out.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2>Hope that helps,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=585030712-29122008><FONT face=Arial
color=#0000ff size=2>Regina</FONT></SPAN></DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<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>nicklas.aven@jordogskog.no<BR><B>Sent:</B> Monday, December 29, 2008 3:18
AM<BR><B>To:</B> postgis-users@postgis.refractions.net<BR><B>Subject:</B>
[postgis-users] Dividing an area to closest line<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV>Hallo</DIV>
<DIV> </DIV>
<DIV>My first time writing here.</DIV>
<DIV> </DIV>
<DIV>The case is that I need to find the closest road from every point in the
terrain. The roads are defined in "roadparts". The very best thing would be to
get polygons around every roadpart which I could use on other data to bind it to
the right road.</DIV>
<DIV> </DIV>
<DIV>The only solution I can see is making a raster of small rektangels that I
bind to my roadparts using nearest neighbour-calculations.</DIV>
<DIV> </DIV>
<DIV>My question is if someone has a more efficient and better solution.</DIV>
<DIV> </DIV>
<DIV>Sorry for my bad english</DIV>
<DIV> </DIV>
<DIV>Thanks</DIV>
<DIV>/Nicklas Avén</DIV></BODY></HTML>
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