[Proj] Status of projection inverses

Gerald I. Evenden geraldi.evenden at gmail.com
Sat Oct 25 22:43:04 EDT 2008

Several days have gone by without any comments on the subject but that does 
not mean that I am not working on it.

1. trying to get a better initial  guess process via some rough polynomial 
method pretty well went up in flames.

2. but using the gsl library of multidimensional root finding shows a great 
deal of progress and converges faster than the simple Newton-Raphson and is 
more tolerant of poor initial conditions.

3. gsl can also do the same job without a Jacobian requiring derivatives.  For 
those who have not already noticed, there are many inverseless projections 
where the derivatives would be impossible or nearly so---even with help from 

Conclusions here are that I am going to finish up this project with the gsl 
methodology in order to preserve my own sanity.  ;-)

The gsl library already requires gsl for one projection so there is nothing 
new in the gsl option.

For those who cannot abide by the gsl license I will continue to use the 
switches in the Makefile to eliminate code that uses that library.  The 
bottom line is that some inverse projections will not be available to non-gsl 
users.  Sorry.

The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist

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