asin( sin( dist_rad / cos(center_lat_rad) ) )

sin(lambda) / sin(r) = sin(90 degrees) / sin(90 - phi)
= 1 / cos(phi).

lambda = ArcSin( sin(r) / cos(phi) ).

sin(phi) = sin(phi') cos(r).

phi' = ArcSin( sin(phi) / cos(r) )