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isn't this the same as putting two geom w/ a meter projection into st_distance(), st_distance() still returns a <FONT face=URWPalladioL-Roma size=2>cartesian distance not a distances in meters? Wouldn't you need to do something like...</FONT><BR>
transform(st_distance(geom,geom),srid)??? <BR>
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I only ask because I am having a simular problem. My projections are in a meter projection, but I can't get st_distance() or st_dwithin() to use meters? any thoughts?<BR><BR><BR>
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Subject: RE: [postgis-users] How to get the distance between geometry in meters?<BR>Date: Wed, 19 Mar 2008 06:56:24 -0400<BR>From: robe.dnd@cityofboston.gov<BR>To: postgis-users@postgis.refractions.net<BR><BR>
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<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>You'll need to transform to a meter based projection to do that. If for example you are in the U.S, SRID 2163 US National Atlas Equal Area works pretty good for measurement. It is not as accurate as UTM or State Plane, but its pretty good and covers all of US I believe and probably works for some of Canada as well (not sure about non-continental e.g. Hawaii, Alaska). </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>e.g.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>SELECT road.rd_name, ht.ht_name, ST_Distance(ST_Transform(roads.the_geom,2163) , ST_Transform(hotel.the_geom,2163)) as dist_meters</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>FROM road, hotel</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>WHERE <some criteria here></FONT></SPAN></DIV></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>If you are somewhere else and your locations are within that projection, you can use that. Look at the utmzone function in the wiki that will help you determing the right UTM zone SRID for your data</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2><A href="http://postgis.refractions.net/support/wiki/index.php?plpgsqlfunctions" target=_blank>http://postgis.refractions.net/support/wiki/index.php?plpgsqlfunctions</A></FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>So you would use something liek</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>SELECT utmzone(ST_Centroid(the_geom)) as srid</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>to get the right UTM zone SRID</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>Hope that helps,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2>Regina</FONT></SPAN></DIV>
<DIV><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=EC_102324810-19032008><FONT face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
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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>Sinboy Chang<BR><B>Sent:</B> Wednesday, March 19, 2008 3:09 AM<BR><B>To:</B> postgis-users@postgis.refractions.net<BR><B>Subject:</B> [postgis-users] How to get the distance between geometry in meters?<BR></FONT><BR></DIV>
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<DIV>i want to get the distance between geometry,just like road or hotel poi,but ST_Distance() return the result in <EM>cartesian dintance.</EM></DIV>
<DIV>So how can get the distance() by meters?</DIV>
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