[Proj] Status of projection inverses

[Gerald I. Evenden]

On Sunday 26 October 2008 12:00:24 am Paul Selormey wrote:
> > Conclusions here are that I am going to finish up this project with the
> > gsl methodology in order to preserve my own sanity.  ;-)
>
> You mean putting the proj4 under GPL? Good luck.

COMMENT #1: libproj4 is already a user of gsl.  If you do not have gsl you do not get the +proj=mayr projection.

Note:

ifdef GSL
gsll = -lgsl -lgslcblas
gslf = -DPROJ_HAVE_GSL=1
endif

is part of the Makefile.  Comment it out if you do not want to use gsl.

As for not using gsl the only additional effect will be not getting inverse operations on certain projections.

COMMENT #2: The root finding system described in the Ipbucker-Bildirici paper is a simplistic solution; one that is much better solved with additional techniques that do better job in terms of fewer iterations as well as recovering from poor initial estimates.  I would be remiss in my attempts to provide quality software by not taking advantage of freely available libraries.

In addition, use of the gsl library offers methods allowing solving inverse projections for which there are no derivatives.

COMMENT #3: In terms of the usage of the gsl library and application of its licensing, *I do not distribute gsl* nor any modification of gsl.  The use of the libproj4 *and* its reference to gsl entry points requires the end user to secure the gsl library and follow GPL.  If you use libproj4 without gsl then there is only the liberal libproj4 license applies.

If anyone believes my logic of the last paragraph is in error, please let me know.

COMMENT #4: For anyone using libproj4 with gsl in their own shop I do not see what the problem is.  If someone is doing a value added piece of softwere for sale using both libproj4 and gsl then there may be a problem.  But I have no experience with such problems and can do nothing but acknowledge that they may exist.

LAST COMMENT: If gsl is untenable but the services it supplies are needed then develop your own code to replace it or find a supplier of a library with tolerable licensing.  My usage of gsl and the services it provides are fairly standard fare. 

-- 
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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