<HTML dir=ltr><HEAD><TITLE>Re: [postgis-devel] Non-Join Join</TITLE>
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<DIV dir=ltr><FONT face=Arial color=#000000 size=2>Martin,</FONT></DIV>
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<DIV dir=ltr>Done. I guess it should go in the official docs too as an example of ST_DWithin.</DIV>
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<DIV dir=ltr><A href="http://postgis.refractions.net/support/wiki/index.php?ExamplesAntiNear">http://postgis.refractions.net/support/wiki/index.php?ExamplesAntiNear</A></DIV>
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<DIV dir=ltr>Also I think Queen is more fitting than master don't you think :)<BR></DIV>
<DIV dir=ltr>Thanks,</DIV>
<DIV dir=ltr>Regina</DIV>
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<DIV dir=ltr><FONT face=Tahoma size=2><B>From:</B> postgis-devel-bounces@postgis.refractions.net on behalf of Martin Davis<BR><B>Sent:</B> Fri 7/18/2008 5:28 PM<BR><B>To:</B> PostGIS Development Discussion<BR><B>Subject:</B> Re: [postgis-devel] Non-Join Join<BR></FONT><BR></DIV>
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<P><FONT size=2>And I nominate you to post this to the PostGIS wiki! 8^)<BR><BR>Martin Davis wrote:<BR>> I bow to the master.<BR>><BR>> Obe, Regina wrote:<BR>>> Wrong Martin. Find all that are within 1000 with a left join using an<BR>>> indexed search and then throw out those that don't have matches.<BR>>> If it has no neighbor within 1000 feet then all its neighbors must be<BR>>> more than 1000 feet away.<BR>>><BR>>> -----Original Message-----<BR>>> From: postgis-devel-bounces@postgis.refractions.net<BR>>> [<A href="mailto:postgis-devel-bounces@postgis.refractions.net">mailto:postgis-devel-bounces@postgis.refractions.net</A>] On Behalf Of<BR>>> Martin Davis<BR>>> Sent: Friday, July 18, 2008 5:21 PM<BR>>> To: PostGIS Development Discussion<BR>>> Subject: Re: [postgis-devel] Non-Join Join<BR>>><BR>>> Since you're trying to find all As which are *further* than a given<BR>>> distance from Bs, I don't think there is any "efficient" way.<BR>>><BR>>> I think you pretty much have to do a self-join with a where condition<BR>>> like "where distance(geomA, geomB) > 1000". Oh, and I guess you'll need<BR>>><BR>>> a filter condition to compare only As and Bs.<BR>>><BR>>> Paul Ramsey wrote:<BR>>> <BR>>>> Brain freeze:<BR>>>><BR>>>> Give a table<BR>>>><BR>>>> gid integer<BR>>>> geom geometry<BR>>>> letter varchar<BR>>>><BR>>>> where letter is a single letter,<BR>>>><BR>>>> how to efficiently find all the instances of the letter 'A' that are<BR>>>> more than 1000m from any letter 'B'.<BR>>>><BR>>>> P.<BR>>>> _______________________________________________<BR>>>> postgis-devel mailing list<BR>>>> postgis-devel@postgis.refractions.net<BR>>>> <A href="http://postgis.refractions.net/mailman/listinfo/postgis-devel">http://postgis.refractions.net/mailman/listinfo/postgis-devel</A><BR>>>><BR>>>> <BR>>><BR>>> <BR>><BR><BR>--<BR>Martin Davis<BR>Senior Technical Architect<BR>Refractions Research, Inc.<BR>(250) 383-3022<BR><BR>_______________________________________________<BR>postgis-devel mailing list<BR>postgis-devel@postgis.refractions.net<BR><A href="http://postgis.refractions.net/mailman/listinfo/postgis-devel">http://postgis.refractions.net/mailman/listinfo/postgis-devel</A><BR></FONT></P></DIV></BODY></HTML>
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