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A Library for Handling
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Description:
This function 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 2dimensional 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.
Synopsis
void astIntersect( AstFrame
$\ast $this,
const double a1[2], const double a2[2], const double b1[2], const double b2[2], double
cross[2] )
Parameters:
this
Pointer to the Frame.
a1
An array of double,
with one element for each Frame axis (
Naxes attribute). This should contain the
coordinates of the first point on the first geodesic curve.
a2
An array of double,
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 coincident
with the first point.
b1
An array of double, with one element for each Frame axis
(Naxes attribute). This should contain the coordinates of the first point on the second
geodesic curve.
b2
An array of double, 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 coincident with the first point.
cross
An array of double, with one element for each Frame axis in which
the coordinates of the required intersection will be returned.
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
coincident, or if the two curves do not intersect.

The geodesic curve used by this function is the path of shortest distance between two
points, as defined by the astDistance function.

An error will be reported if the Frame is not 2dimensional.
Copyright (C) 2021 East Asian Observatory
 ←Prev
 AST
A Library for Handling
World
Coordinate Systems
in Astronomy  Next→
 TOC ↑