<HTML dir=ltr><HEAD><TITLE>Re: [postgis-users] Does ST_AsText truncate or round</TITLE>
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<DIV dir=ltr><FONT face=Arial color=#000000 size=2>Havard,</FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>I think as Mark mentioned if it did it would violate the spec. I think somewhere in the spec is some specification of guaranteed precision of WKT and if there isn't - text can never represent floating to complete accuracy. The AsBinary I think on the other hand is exact fidelity. So simply trying to make them equal would probably irritate people who need precision higher than what the WKT spec offers.</FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>In my particular case of course this would be ideal - but I can't be selfish :)</FONT></DIV>
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<DIV dir=ltr><FONT face=Arial size=2>So I can live with the general rule that </FONT></DIV>
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<DIV dir=ltr><FONT size=2>ST_GeomFromText(ST_AsText(geom), srid here) != geom</FONT></DIV><FONT size=2></FONT></DIV>
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<DIV dir=ltr><FONT size=2>As long as I can override it by updating my millions of geometries to so and 300 someodd tables with </FONT></DIV>
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<DIV dir=ltr><FONT size=2>SET the_geom = ST_GeomFromText(ST_AsText(geom))</FONT></DIV>
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<DIV dir=ltr><FONT size=2>without too many weird side effects. I may just try it and see if it causes other problems elsewhere.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>testing with the badly edited records it seems to at least make my other geometries just as inprecise as the edited ones so I get intersection where I should again.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>Thanks,</FONT></DIV>
<DIV dir=ltr><FONT size=2>Regina</FONT></DIV>
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<FONT face=Tahoma size=2><B>From:</B> postgis-users-bounces@postgis.refractions.net on behalf of Havard Tveite<BR><B>Sent:</B> Fri 5/16/2008 2:41 PM<BR><B>To:</B> PostGIS Users Discussion<BR><B>Subject:</B> Re: [postgis-users] Does ST_AsText truncate or round<BR></FONT><BR></DIV>
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<P><FONT size=2>Sorry, for not making much sense here. What I wanted to<BR>say was that ST_AsText(geom) should be equivalent to geom,<BR>meaning that if you go from the database/binary<BR>representation of the geometry to the text representation<BR>of the geometry (using ST_AsText) and then back to the<BR>database/binary representation (using ST_GeomFromText),<BR>you should end up with the same geometry that you<BR>started out with. This is important for applications<BR>that use when WKT when talking to PostGIS.<BR><BR>Håvard<BR><BR><BR>Mark Cave-Ayland wrote:<BR>> Håvard Tveite wrote:<BR>>> ST_GeomFromText(ST_AsText(geom)) != geom<BR>>><BR>>> sounds like a bug to me (ignoring the SRS).<BR>>><BR>>> Håvard<BR>><BR>> No, since the SFS 1.1 specification supports only 2 dimensions with no<BR>> SRS (and ST_AsText() is spec compliant). If you need the SRS then you<BR>> should use the PostGIS-enhanced ST_EWKT() function which will output the<BR>> extra information, but is not spec-compliant.<BR>><BR>><BR>> ATB,<BR>><BR>> Mark.<BR>><BR>> --<BR>> Mark Cave-Ayland<BR>> Sirius Corporation - The Open Source Experts<BR>> <A href="http://www.siriusit.co.uk/">http://www.siriusit.co.uk</A><BR>> T: +44 870 608 0063<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>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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