astIntersect
-
Find the point of intersection between two geodesic curves
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 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.
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
co-incident 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
co-incident 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 co-incident, 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 2-dimensional.
AST A Library for Handling World Coordinate Systems in Astronomy Starlink User Note 211 R.F. Warren-Smith & D.S. Berry 24th May 2011 E-mail:ussc@star.rl.ac.uk
Copyright (C) 2009 Science \& Technology Facilities Council