[Proj] Re: Discovery: libproj4 stmerc = French Gauss-Laborde projection

[Strebe at aol.com]

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:

http://mapthematics.com/Projection%20Images/Cylindrical/Transverse%20Mercator.
GIF

The method works for arbitrary eccentricities. Contact me privately if you're 
interested. Since it is Dr. Wallis's invention, I'll put you in contact with 
him. 

Regards,
-- daan Strebe


In a message dated 6/13/06 12:03:39, ovv at hetnet.nl writes:


> > BTW: what did you use to get the "exact" values?
> My own stuff.
> I had a very hard time finding solid code. Several people are guarding the
> principles as a secret and are deliberately vague. Or they are trying to get
> solid money from it by selling software or books.
> But I persevered in trying to get the Dozier show on the road.
> You (mr. Evenden) already found one error in his code, but this error has to
> be corrected in 3 places. It's the error of the elliptic parameter m, which
> has to be the elliptic modulus k in 3 cases (tmfd, gk, tmid).
> It appeared that the Dozier code - the complex Newton iteration - was
> useless in some regions, especially large lon-lon0 and low latitudes. First
> I used somewhat better elliptic functions from Cernlib. But, to more effect,
> I concocted another iteration scheme based on TOMS algorithm 365, a very
> slow downhill walkaround method, yet very powerful.
> I checked my results with an on-line calculator from professor Schuhr, based
> on the Klotz algorithms.
> <http://gauss.fb1.fh-frankfurt.de/cgi-bin/cgi_gk>
> This calculator fails for difficult areas (very large lon-lon0, small lat).
> So I can only 'proof' my results in the difficult areas by doing a complete
> round-trip and getting nearly the original data back.
> And yes, I do the lon-lon0=90 degrees too.
> 
> 

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