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A Library for Handling
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Description:
This
routine finds the angle at point B between the line joining points A and B, and the line joining points
C and B. These lines will in fact be geodesic curves appropriate to the
Frame in use. For
instance, in
SkyFrame, they will be great circles.
Invocation
RESULT = AST_ANGLE( THIS, A,
B, C, 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.
C(
) =
DOUBLE PRECISION (Given)
An array with one element for each Frame axis (Naxes attribute)
containing the coordinates of the third point.
STATUS = INTEGER (Given and Returned)
The
global status.
Returned Value
AST_ANGLE = DOUBLE PRECISION
The angle in
radians, from the line AB to the line CB. If the Frame is 2-dimensional, it will be in the range
$pm
pi$, 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:
-
A value of AST__BAD will also be returned if points A and B are co-incident, or if points B and C are
co-incident.
-
A value of AST__BAD will also be returned if this function is invoked with STATUS set to an error
value, or if it should fail for any reason.
Copyright (C) 2021 East Asian Observatory
- ←Prev
- AST
A Library for Handling
World Coordinate
Systems
in Astronomy - Next→
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