[postgis-users] Comparing two WKT... howto?

[Frank Warmerdam]

Luigi Pirelli wrote:
> A.WKT->exportToProj4 = "+proj=utm +zone=32 +ellps=intl 
> +towgs84=-87.000,-98.000,-121.000 +units=m +no_defs"
> 
> B.WKT->->exportToProj4 = "+proj=utm +zone=32 +ellps=intl +units=m +no_defs"
> 
> differs only in +towgs84 string.

Luigi,

Well, these coordinate system do really differ since one has a well
defined relationship to the WGS84 datum and one does not.  It would indeed
take a fairly specific test to ignore this sort of difference.  You
would almost need an IsCompatible() test to mean can these two coordinate
systems potentially be the same.

I would add that it is annoying neither the GRASS nor PostGIS WKT
definitions include the authority tags.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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