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A Library for Handling
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Description:
This
routine finds the coordinate values at the point of intersection between two geodesic curves.
Each curve is specified by two points on the curve. It can only be used with 2-dimensional
Frames.
For example, in a basic Frame, it will find the point of intersection between two straight lines. But for a
SkyFrame it will find an intersection of two great circles.
Invocation
CALL AST_INTERSECT( THIS,
A1, A2, B1, B2, CROSS, STATUS )
Arguments
THIS = INTEGER (Given)
Pointer to the Frame.
A1( 2 ) = DOUBLE PRECISION (Given)
An array with one element for each Frame axis (
Naxes
attribute). This should contain the coordinates of the first point on the first geodesic curve.
A2( 2 ) =
DOUBLE PRECISION (Given)
An array with one element for each Frame axis (Naxes
attribute). This should contain the coordinates of a second point on the first geodesic curve. It
should not be co-incident with the first point.
B1( 2 ) = DOUBLE PRECISION (Given)
An array with one element for each Frame axis (Naxes attribute). This should contain the
coordinates of the first point on the second geodesic curve.
B2( 2 ) = DOUBLE PRECISION
(Given)
An array with one element for each Frame axis (Naxes attribute). This should
contain the coordinates of a second point on the second geodesic curve. It should not be
co-incident with the first point.
CROSS( 2 ) = DOUBLE PRECISION (Returned)
An array with
one element for each Frame axis in which the coordinates of the required intersection will
be returned.
STATUS = INTEGER (Given and Returned)
The global status.
Notes:
-
For SkyFrames each curve will be a great circle, and in general each pair of curves will intersect at two
diametrically opposite points on the sky. The returned position is the one which is closest to point
A1.
-
This function will return " bad" coordinate values (AST__BAD) if any of the input coordinates has this
value, or if the two points defining either geodesic are co-incident, or if the two curves do not
intersect.
-
The geodesic curve used by this routine is the path of shortest distance between two points, as defined
by the AST_DISTANCE function.
-
An error will be reported if the Frame is not 2-dimensional.
Copyright (C) 2021 East Asian Observatory
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- AST
A Library for Handling
World Coordinate
Systems
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