astOffset2astOffset2
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Calculate an offset along a geodesic curve in a 2D Frame
Description:
This function finds the FrameFrame 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 2-dimensional 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.
An array of double, with one element for each Frame axis
(NaxesNaxes 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
astDistanceastDistance function.
An error will be reported if the Frame is not 2-dimensional.
This function will return "bad" coordinate values (AST__BAD)
if any of the input coordinates has this value.