[Proj] Unknown projection?

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"Gerald I. Evenden" <geraldi.evenden at gmail.com> kirjoitti: 
> On Saturday 13 September 2008 10:59:24 am Paul B. Anderson wrote:
> > - Janne,
> >
> > Your map graphic appears to be in the Winkel Tripel map projection. I would
> > also suggest that it is using Oswald Winkel's original selection of
> > 50.46667 degrees as the Special Parallel.
> >
> > Note that by the 1950s John Bartholomew was using a special parallel of 40
> > degrees for his version of the Tripel, giving his graphic a more flattened
> > appearance in the Y direction.
> 
> This is exactly why I include the projection math in the manual.  The factor 
> Anderson is discussing is +lat_1 option for the +proj=wintri projection.  
> Select your own option value and name a new projection.  ;-)
> 

Ok, now the problem seems to be that "wintri" does not have any inverse projection
available. What is the reason not to have inverse projections for all routines
in the library... math is too hard?

Janne.