| pe_mu_to_phi | 
Calculates the geographic latitude from the rectifying latitude
double pe_mu_to_phi (double e2, double mu);
| e2 | Eccentricity squared of the spheroid | 
| mu | Rectifying latitude (measured in radians) of the point | 
This function is the inverse of pe_phi_to_mu; pe_mu_to_phi(e2,pe_mu(e2,phi)) is approximately equal to phi.

where

Geographic latitude (measured in radians) of the point