Brent, Ah never mind. For some reason I was under the false assumption that in SQL Server with dictionary sort order that even though
REGINA = Regina That I would get 2 Reginas when I union them. That is not the case. I just get one. I'm not sure why I thought that or maybe it was like that a long time ago. Anyrate - so I guess I am back to square one. By the way - I think we should be talking about ST_OrderingEquals not ST_Equals. I'm not sure which if any of those PostGIS is using to do the check, but it should be ST_OrderingEquals since using ST_Equals introduces a whole lot more philosophical can of worms. Is space empty or is Empty space. Thanks, Regina -----Original Message----- From: Brent Wood [mailto:[EMAIL PROTECTED] Sent: Sunday, September 28, 2008 3:19 PM To: [EMAIL PROTECTED] Subject: RE: [postgis-users] Re: Comparing Geometries with Different SRIDs Hi Regina, I think that is more an encoding/language issue than case in such an analogy. To wax metaphysical, does a muslim worship a different god because they spell it allah? (Similarly Jews with Jehovah & French with dieu...) So is st_equals() a cross-language thesaurus, or is it restricted to the specified SRID? :-) Spotcha, Brent Wood --- On Mon, 9/29/08, Paragon Corporation <[EMAIL PROTECTED]> wrote: > From: Paragon Corporation <[EMAIL PROTECTED]> > Subject: RE: [postgis-users] Re: Comparing Geometries with Different > SRIDs > To: "'PostGIS Users Discussion'" > <[email protected]> > Date: Monday, September 29, 2008, 8:04 AM Charlie, > > On second thought not sure how DB II deals with relational Union of > geometries. Does anybody have that by chance to test? > > I suppose we could say this is the same deal as difference in casing. > > SELECT 'Regina' > UNION > SELECT 'REGINA' > UNION > SELECT 'Regina' > > Even if both geometries are the same which SRID would you choose? So > we should not be doing a geometry compare, but a binary compare. > > SELECT ST_AsEWKB('SRID=4269;POINT(1 3)') = > ST_AsEWKB('SRID=4326;POINT(1 3)') > > > Thanks, > Regina > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > Paragon Corporation > Sent: Sunday, September 28, 2008 2:48 PM > To: 'PostGIS Users Discussion' > Subject: RE: [postgis-users] Re: Comparing Geometries with Different > SRIDs > > I feel your pain Charlie, but I'm on Reid's side. > Given that some spatial > databases do support cross compare between geometries of different > SRID (e.g. DB II), not sure about Oracle or SQL Server 2008, I would > prefer an answer that is in compliance or throws an exception when it > can't be sure. > Its annoying from a debugging perspective to deal with things that > fail silently. Returning false is a fail silently in my book. > > If we deal with this as a special case - why wouldn't we deal with > everything else the same with every other relational compare we do? > Its just wrong, but granted doing the wrong thing would be > conveniently useful in many cases. > > Thanks, > Regina > > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > Charlie Savage > Sent: Sunday, September 28, 2008 2:10 PM > To: PostGIS Users Discussion > Subject: Re: [postgis-users] Re: Comparing Geometries with Different > SRIDs > > > > Reid Priedhorsky wrote: > > Charlie Savage wrote: > >>> The 2 point could be spatially equal given > different SRIDS and > >>> coordinates if they were projected to a common > SRID. So should > >>> geometry operators silently Call st_transform > to make the righthand > >>> match the lefthand before comparing? This > would be quite the > >>> expensive operation. > >> > >> No. You can't automatically transform between > different SRID values > >> Think of the case of one geometry with an SRID > value of 4326 and one > >> with an SRID value of -1 (no coordinate system). > > > > Exactly. > > > >> So different SRID values, then the geometries are > not equal. > > > > No -- as Stanley said, the geometries could be in fact > equal, but > > expressed in different SRS. So if ST_Equals() returned > False, it would > > be wrong. > > Maybe. But returning "Operation permitted" is even worse because it > means you can't do natural things like this (without extra annoying > SRID checking > code) in plpgsql: > > IF (geom1 == geom2) ... END IF; > > Or the example with the union earlier posted > > > >> It is up to the user to transform geometries to > the same SRID before > >> calling ST_EQUALS. > > > > Exactly. ;) > > So, I still vote that st_equals will not blow up when comparing two > geometries with different SRID values, it just will return false. > > Charlie > > > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > > > > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
