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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 at a given angle from a specified
starting point. It can only be used with 2dimensional Frames.
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
double astOffset2(
AstFrame $\ast $this,
const double point1[2], double angle, double offset, double point2[2] );
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.
angle
The angle (in radians) from the positive
direction of the second axis, to the direction of the required position, as seen from
the starting position. Positive rotation is in the sense of rotation from the
positive direction of axis 2 to the positive direction of axis 1.
offset
The required offset from the first point along the geodesic curve. If this is
positive, it will be in the direction of the given angle. If it is negative, it
will be in the opposite direction.
point2
An array of double, with one
element for each Frame axis in which the coordinates of the required point will
be returned.
Returned Value
astOffset2
The direction of the geodesic
curve at the end point. That is, the angle (in radians) between the positive
direction of the second axis and the continuation of the geodesic curve at the
requested end point. Positive rotation is in the sense of rotation from the
positive direction of axis 2 to the positive direction of axis 1.
Notes:

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.

This function will return "
bad"
coordinate values (AST__BAD) if any of the input
coordinates has this value.
Copyright (C) 2021 East Asian Observatory
 ←Prev
 AST
A Library for Handling
World
Coordinate Systems
in Astronomy  Next→
 TOC ↑