[Proj] Re: Discovery: libproj4 stmerc = French Gauss-Laborde
Oscar van Vlijmen
ovv at hetnet.nl
Wed Jun 14 14:00:57 EDT 2006
> You might contact Dr. David E. Wallis. He devised a much simpler method than
> Dozier's. I've implemented it for the full-ellipsoid. You can see a plot of an
> earth-like ellipsoid here:
Thanks for the nice picture!
A word of caution for all TM methods:
it is very difficult to get any accuracy at the edges, i.e. for very large
lon-lon0 at small values of lat, and very near the poles. Let's not
exaggerate our claims!
By using for instance an approximation like the Finnish Julkisen Hallinnon
Suositus or the French IGN uses, even the mathematical singularity at the
poles (lat=90) seems to vanish (Wallis claim).
It apparently seems not too difficult to devise a reasonable TM
approximation for the entire (hemi)sphere, good enough for large-scale
mapping. But to get high accuracy at the edges is very difficult.
>> I checked my results with an on-line calculator from professor Schuhr,
>> based on the Klotz algorithms.
> And working in Grads is a bit of a nuisance.
The German 'Grad' is the English 'degree'.
English 'grad' was in German 'Neugrad', now 'Gon'.
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