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eraPas

rv = ERFA.pas(al, ap, bl, bp)

Position-angle from spherical coordinates.

Given:

   al     double     longitude of point A (e.g. RA) in radians
   ap     double     latitude of point A (e.g. Dec) in radians
   bl     double     longitude of point B
   bp     double     latitude of point B

Returned (function value):

          double     position angle of B with respect to A

Notes:

  1. The result is the bearing (position angle), in radians, of point B with respect to point A. It is in the range -pi to +pi. The sense is such that if B is a small distance "east" of point A, the bearing is approximately +pi/2.

  2. Zero is returned if the two points are coincident.

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.