[Proj] +towgs84 approximation error

[Jochem]

Hi Martin,

WGS84 is just a hub for many users. I will transform data from frame A via
WGS84 to frame B. The transformation from A to B should have 1 mm (not 0.1
mm) accuracy for me, since the coordinates are of 1 cm accuracy. 

Moreover, 7 parameter transformations are not always stochastic, e.g. the
transformation between the Dutch national grid and ETRS89 (=WGS84 +/- 1 m)
is by definition exact since the Dutch national grid is defined as the
transformation from ETRS89.

Furthermore, world wide geodetic positional accuracy in ITRF (=WGS84 +/-
0.0001 m) is possible well below the accuracy of the 4 cm error I am
experiencing.

I think these are 3 reasons why the approximation is not good enough and
should be improved.

Regards, Jochem  
 



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