[Proj] Belge 1972 / Belgian Lambert 72 (31370) - towgs84parameters

Jan Hartmann j.l.h.hartmann at uva.nl
Fri Jan 22 10:03:34 EST 2010

On 22-1-2010 15:40, Mikael Rittri wrote:
> Jan, you wrote
> > All my observations about the towgs parameters have been tested with 
> real Belgian coordinates overlaid over Google.
> Fine.  But if you did make an error when transcribing the newer 
> transforms into Proj.4 syntax, and
> the error was just in the rotation angles, then the effect may be too 
> small to notice.
> I mean, the angles describe a rotation, so there is presumably a fixed 
> point in Belgium where
> the rotation has no effect.  If your test points happened to be near 
> the fixed point, the
> effect of the reversed angle signs could be very small.
> > As I said before, the EPSG database is not very systematical in the 
> way it represents its formulas,
> > it just takes them from whatever source is available, untested AFAIK. 
> Never use them without testing them with real world coordinates.
> I agree completely.  But I am not yet convinced that you are right and 
> EPSG wrong for the newer transforms,
> although that is certainly possible.  Do you have some link to the 
> offician Belgian documents?

As I said in a previous email:

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