eraSepp

rv = ERFA.sepp(a, b)

Angular separation between two p-vectors.

Given:

   a      double[3]    first p-vector (not necessarily unit length)
   b      double[3]    second p-vector (not necessarily unit length)

          double       angular separation (radians, always positive)

If either vector is null, a zero result is returned.
The angular separation is most simply formulated in terms of scalar product. However, this gives poor accuracy for angles near zero and pi. The present algorithm uses both cross product and dot product, to deliver full accuracy whatever the size of the angle.

   eraPxp       vector product of two p-vectors
   eraPm        modulus of p-vector
   eraPdp       scalar product of two p-vectors

This revision: 2021 May 11