**ACTION:**- Returns the bearing (position angle) of one point on a
sphere seen from another (single precision).
**CALL:**`R = sla_BEAR (A1, B1, A2, B2)`

**GIVEN:**-

*A1,B1***R**spherical coordinates of one point *A2,B2***R**spherical coordinates of the other point

**RETURNED:**-

*sla_BEAR***R**bearing from first point to second

**NOTES:**- 1.
- The spherical coordinates are ,
*etc.*, in radians. - 2.
- 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.
- 3.
- If either B-coordinate is outside the range , the result may correspond to ``the long way round''.
- 4.
- The routine sla_PAV performs an equivalent function except that the points are specified in the form of Cartesian unit vectors.

Starlink User Note 67

P. T. Wallace

12 October 1999

E-mail:ptw@star.rl.ac.uk