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A Library for Handling
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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)
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.
Copyright (C) 2021 East Asian Observatory
- ←Prev
- AST
A Library for Handling
World Coordinate
Systems
in Astronomy - Next→
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