R: [postgis-users] precision of GeomFromTex, Transform and text functions

[Frank Koormann]

* Ludovico Bianchini <metlud at yahoo.it> [070904 16:03]:
> I have this question: is there a parameter simmetric
> to TOWGS? If so the project library shall use FROMWGS
> to convert from the gps system and TOWGS to convert to
> the gps system.
> Sorry if the question is stupid, but I don't
> understand how to solve this problem (to convert gps
> (SRID=4326) to West Gauss Boaga Italy Rome Monte Mario
> (SRID=26591 or 3003).

The towgs84 (note the 84!) decribes a correction performed by a
bijective matrix multiplication. Hence the inverse can be used
for the other direction "from" wgs. Proj4 does this automatically.

Regards,

        Frank

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