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A Library for Handling
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Description:
This
function finds the
Frame coordinate values of a point which is offset a specified
distance along the geodesic curve between two other points.
For example, in a basic Frame, this offset will be along the straight line joining two
points. For a more specialised Frame describing a sky coordinate system, however, it would
be along the great circle passing through two sky positions.
Synopsis
void astOffset(
AstFrame $\ast $this,
const double point1[], const double point2[], double offset, double point3[] )
Parameters:
this
Pointer to the Frame.
point1
An array of double, with one
element for each Frame axis (
Naxes attribute). This should contain the coordinates of
the point marking the start of the geodesic curve.
point2
An array of double, with
one element for each Frame axis This should contain the coordinates of the point
marking the end of the geodesic curve.
offset
The required offset from the first
point along the geodesic curve. If this is positive, it will be towards the second
point. If it is negative, it will be in the opposite direction. This offset need not
imply a position lying between the two points given, as the curve will be extrapolated
if necessary.
point3
An array of double, with one element for each Frame axis
in which the coordinates of the required point will be returned.
Notes:

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

This function will return "
bad"
coordinate values (AST__BAD) if any of the input
coordinates has this value.

"
Bad"
coordinate values will also be returned if the two points supplied are
coincident (or otherwise fail to uniquely specify a geodesic curve) but the requested
offset is nonzero.
Copyright (C) 2020 East Asian Observatory
 ←Prev
 AST
A Library for Handling
World
Coordinate Systems
in Astronomy  Next→
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