[Proj] Question for the math types

[support.mn at elisanet.fi]

"Gerald I. Evenden" <geraldi.evenden at gmail.com> kirjoitti: 
> Several projections are in the form f(phi,lam,t) where t is a third equation 
> typically requiring Newton-Raphson for solution.
> 
> Question: what is the name of the function of t?
>

I am not a specialist in that area, but the following link?

http://en.wikipedia.org/wiki/Spherical_coordinate_system

Janne.