<HTML dir=ltr><HEAD><TITLE>Re: [postgis-users] ST_Difference</TITLE>
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<DIV dir=ltr><FONT face=Arial color=#000000 size=2>Oops even easier</FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>SELECT pd.*</FONT></DIV>
<DIV dir=ltr><FONT face=Arial size=2>FROM pandatestdata p LEFT JOIN <FONT face="Times New Roman">world2_12nm w On st_contains(w.the_geom, p.the_geom)</FONT></FONT></DIV>
<DIV dir=ltr><FONT size=2>WHERE w.id IS NULL</FONT></DIV>
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<DIV dir=ltr><FONT size=2>Here I am assuing w.id is the id of world2_12nm</FONT></DIV></DIV>
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<FONT face=Tahoma size=2><B>From:</B> postgis-users-bounces@postgis.refractions.net on behalf of Paul Ramsey<BR><B>Sent:</B> Wed 10/24/2007 5:01 PM<BR><B>To:</B> Richard.Heimann@nrl.navy.mil<BR><B>Cc:</B> 'PostGIS Users Discussion'<BR><B>Subject:</B> Re: [postgis-users] ST_Difference<BR></FONT><BR></DIV>
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<P><FONT size=2>Oh, yeah, oops, I know. It's the join logic, its finding the things <BR>not contained for each world feature, not for the full world set.<BR><BR>select pd.* from pandatestdata pd,<BR>(select p.id<BR>from pandatestdata p, world2_12nm w<BR>where st_contains(w.the_geom, p.the_geom)) as wd where pd.id <> wd.id;<BR><BR>Ugly, but probably effective: find all the things contained, then <BR>just strip those out.<BR><BR>The trouble is that disjointness is not an easily spatially indexable <BR>operation. If you're going to take this into operation with large <BR>data volumes, a more effective data set would be ocean polygons, cut <BR>up into smallish regular grid squares, then you can test containment <BR>with relatively good index selectivity.<BR><BR>P.<BR><BR>On 24-Oct-07, at 1:53 PM, Richard Heimann [C] wrote:<BR><BR>> Thanks Paul for the response. I hadn’t thought of this logic, it <BR>> didn’t work<BR>> however. Strangely, it increased the number of features by eight <BR>> times. Any<BR>> thoughts?<BR>><BR>> Vr<BR>> Rich<BR>><BR>><BR>><BR>> -----Original Message-----<BR>> From: Paul Ramsey [<A href="mailto:pramsey@refractions.net">mailto:pramsey@refractions.net</A>]<BR>> Sent: Wednesday, October 24, 2007 4:07 PM<BR>> To: Richard.Heimann@nrl.navy.mil; PostGIS Users Discussion<BR>> Subject: Re: [postgis-users] ST_Difference<BR>><BR>> select p.*<BR>> from pandatestdata p, world2_12nm w<BR>> where not st_contains(w.the_geom, p.the_geom);<BR>><BR>> On 24-Oct-07, at 11:45 AM, Richard Heimann [C] wrote:<BR>><BR>>> Thanks for your response W. I should have posted the sql query<BR>>> earlier.<BR>>> Anyway...its below.<BR>>><BR>>> My goal is to drop all features (points) that fall within my<BR>>> polygon. In<BR>>> this case, I have ship track data and want to filter it with world<BR>>> country<BR>>> buffers.<BR>>><BR>>> World2_12nm - my world country 12nm buffered polygon<BR>>> Pandatestdata - track data (point)<BR>>> Panda_diff2 - new table<BR>>><BR>>><BR>>> CREATE TABLE panda_diff2 AS<BR>>> SELECT AsText(Difference(world2_12nm.the_geom,<BR>>> pandatestdata.the_geom)) FROM<BR>>> world2_12nm, pandatestdata<BR>>><BR>>> Also attached are the astext versions of my data as well as a csv<BR>>> of the<BR>>> output from the above sql. Please debunk the mystery...<BR>>><BR>>> Thanks again<BR>>> Rich<BR>>><BR>>> -----Original Message-----<BR>>> From: Webb Sprague [<A href="mailto:webb.sprague@gmail.com">mailto:webb.sprague@gmail.com</A>]<BR>>> Sent: Wednesday, October 24, 2007 12:00 PM<BR>>> To: Richard.Heimann@nrl.navy.mil; PostGIS Users Discussion<BR>>> Subject: Re: [postgis-users] ST_Difference<BR>>><BR>>> You might get more useful help if you post an "astext()" version of<BR>>> your data, the query, the result, and a *desired* result.<BR>>><BR>>> I know the difference functions can be tricky and are sometiimes<BR>>> defined in ways you might not expect.<BR>>><BR>>> Thx<BR>>> W<BR>>><BR>>> On 10/24/07, Richard Heimann [C] <heimann@ait.nrl.navy.mil> wrote:<BR>>>><BR>>>><BR>>>><BR>>>><BR>>>> All,<BR>>>><BR>>>><BR>>>><BR>>>> I would appreciate help in constructing an SQL statement that<BR>>>> performs a<BR>>>> difference function on two datasets. My intersect function works but<BR>>> cannot<BR>>>> work out the kinks with st_difference. Thanks for your help.Im <BR>>>> new to<BR>>>> Postgis.<BR>>>><BR>>>><BR>>>><BR>>>> Rich<BR>>>><BR>>>><BR>>>><BR>>>><BR>>>> _______________________________________________<BR>>>> postgis-users mailing list<BR>>>> postgis-users@postgis.refractions.net<BR>>>> <A href="http://postgis.refractions.net/mailman/listinfo/postgis-users">http://postgis.refractions.net/mailman/listinfo/postgis-users</A><BR>>>><BR>>>><BR>>><BR>>><BR>>><BR>>> _______________________________________________<BR>>> postgis-users mailing list<BR>>> postgis-users@postgis.refractions.net<BR>>> <A href="http://postgis.refractions.net/mailman/listinfo/postgis-users">http://postgis.refractions.net/mailman/listinfo/postgis-users</A><BR>><BR>> <panda_diff2.csv><BR><BR>_______________________________________________<BR>postgis-users mailing list<BR>postgis-users@postgis.refractions.net<BR><A href="http://postgis.refractions.net/mailman/listinfo/postgis-users">http://postgis.refractions.net/mailman/listinfo/postgis-users</A><BR></FONT></P></DIV></BODY></HTML>
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