A map projection. The inverse equations for are computed by iteration. Let the angle of the projection plane be . Define
(1)

For proper convergence, let and compute the initial point by checking
(2)

As long as , take and iterate again. The first value for which is then the starting point. Then compute
(3)

until the change in between evaluations is smaller than the acceptable tolerance. The (inverse) equations are then given by
(4)
 
(5)
