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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) 2014 Science & Technology Facilities Council
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- AST
A Library for Handling
World
Coordinate Systems
in Astronomy - Next→
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