Direction cosines to spherical coordinates. (double precision)
v double[3] x,y,z vector
*a,*b double spherical coordinates in radians The spherical coordinates are longitude (+ve anticlockwise looking from the +ve latitude pole) and latitude. The Cartesian coordinates are right handed, with the x axis at zero longitude and latitude, and the z axis at the +ve latitude pole. If v is null, zero a and b are returned. At either pole, zero a is returned. P.T.Wallace Starlink 31 October 1993