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AST_AXANGLE
-
Returns the angle from an axis, to a line through two points
- Description:
- This routine
finds the angle, as seen from point A, between the positive
direction of a specified axis, and the geodesic curve joining point
A to point B.
- Invocation:
- RESULT = AST_AXANGLE( THIS, A, B, AXIS, STATUS )
- Arguments:
-
THIS = INTEGER (Given)
-
Pointer to the Frame.
-
A(
) = DOUBLE PRECISION (Given)
-
An array with one element for each Frame axis
(Naxes attribute) containing the coordinates of the first point.
-
B(
) = DOUBLE PRECISION (Given)
-
An array with one element for each Frame axis
(Naxes attribute) containing the coordinates of the second point.
-
AXIS = INTEGER (Given)
-
The number of the Frame axis from which the angle is to be
measured (axis numbering starts at 1 for the first axis).
-
STATUS = INTEGER (Given and Returned)
-
The global status.
- Returned Value:
-
AST_AXANGLE = DOUBLE PRECISION
-
The angle in radians, from the positive direction of the
specified axis, to the line AB. If the Frame is 2-dimensional,
it will be in the range [-PI/2,
PI/2], and positive rotation is in
the same sense as rotation from the positive direction of axis 2
to the positive direction of axis 1. If the Frame has more than 2
axes, a positive value will always be returned in the range zero
to PI.
- Notes:
- The geodesic curve used by this routine is the path of
shortest distance between two points, as defined by the
AST_DISTANCE function.
- This function will return "bad" coordinate values (AST__BAD)
if any of the input coordinates has this value, or if the require
position angle is undefined.
Next: AST_AXDISTANCE - Find the distance between two axis values
Up: AST Routine Descriptions
Previous: AST_ANNUL - Annul a pointer to an Object
AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk
Copyright (C) 2009 Science \& Technology Facilities Council