Returns the bearing (position angle) of one point on a
sphere seen from another (single precision).
R = sla_BEAR (A1, B1, A2, B2)
spherical coordinates of one point
spherical coordinates of the other point
bearing from first point to second
The spherical coordinates are , etc., in radians.
The result is the bearing (position angle), in radians,
of point [A2,B2] as seen
from point [A1,B1]. It is in the range . The sense
is such that if [A2,B2]
is a small distance due east of [A1,B1] the result
is about . Zero is returned
if the two points are coincident.
If either B-coordinate is outside the range , the
result may correspond to ``the long way round''.
The routine sla_PAV performs an equivalent function except
that the points are specified in the form of Cartesian unit