Routine to convert the position angles $(\theta,\phi)$ of a point on the sphere into its 3D position vector (x,y,z) with $x = \sin\theta\cos\phi$ , $y=\sin\theta\sin\phi$ , $z=\cos\theta$ .

Location in HEALPix directory tree: src/C/subs/ang2vec.c

FORMAT

name & dimensionality	kind	in/out	description

theta	double	IN	colatitude in radians measured southward from north pole (in [0, $\pi$ ]).
phi	double	IN	longitude in radians measured eastward (in [0, $2\pi$ ]).
vector(3)	double	OUT	three dimensional cartesian position vector (x,y,z). The north pole is (0,0,1)