[Proj] Unknown projection?
Gerald I. Evenden
geraldi.evenden at gmail.com
Sat Sep 13 13:40:12 EDT 2008
On Saturday 13 September 2008 12:26:58 pm Paul B. Anderson wrote:
> - Janne,
> The difficulty comes about because the Tripel is actually composed of 2 map
> projections -- the Aitoff (pronounced 'I-toff') projection averaged with
> the Equirectangular projection (which provides the Special Parallel input).
> Yes, there are inverse formulas out there for the Tripel, but the values
> produced are approximations.
> One person who has researched the inverse Winkel Tripel formulas issue is
> Dr. Robert Schmunk http://www.giss.nasa.gov/staff/rschmunk.html
> BTW, a reference for this map projection is Snyder's 'Flattening the
> Paul B. Anderson FCCS (USN, Retired)
> Kingsport, TN native living in Norfolk, VA
> My Map Projection web site:
> ----- Original Message -----
> From: <support.mn at elisanet.fi>
> To: "PROJ.4 and general Projections Discussions" <proj at lists.maptools.org>;
> <geraldi.evenden at gmail.com>
> Sent: Saturday, September 13, 2008 11:42 AM
> Subject: Re: [Proj] Unknown projection?
> > "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.
I can't find any reference on his website to research on Winkel Tripel so I
suspect he has not published it.
I take back my comment on ease of solution but it would seem to be invertible
using iterative techniques---but slow. Accuracy should only be dependent
upon how many cpu ticks you want to give it.
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
More information about the Proj