 ←Prev
 AST
A Library for Handling
World Coordinate Systems
in Astronomy  Next→
 TOC ↑
Description:
This function finds the angle at point B between the line
joining points A and B, and the line joining points C and B. These lines will
in fact be geodesic curves appropriate to the
Frame in use. For instance, in
SkyFrame, they will be great circles.
Synopsis
double astAngle( AstFrame
$\ast $this,
const double a[], const double b[], const double c[] )
Parameters:
this
Pointer to the Frame.
a
An array of double, with one element for each Frame
axis (
Naxes attribute) containing the coordinates of the first point.
b
An array of double, with one element for each Frame axis (Naxes attribute)
containing the coordinates of the second point.
c
An array of double, with one
element for each Frame axis (Naxes attribute) containing the coordinates of the
third point.
Returned Value
astAngle
The angle in radians, from the
line AB to the line CB. If the Frame is 2dimensional, it will be in the range
$$\setminus $pm
$\setminus $pi$,
and positive rotation is in the same sense as rotation from the positive
direction of axis 2 to the positive direction of axis 1. If the Frame has more
than 2 axes, a positive value will always be returned in the range zero to
$$\setminus $pi$.
Notes:

A value of AST__BAD will also be returned if points A and B are coincident, or if
points B and C are coincident.

A value of AST__BAD will also be returned if this function is invoked with the AST
error status set, or if it should fail for any reason.
Copyright (C) 2019 East Asian Observatory
 ←Prev
 AST
A Library for Handling
World
Coordinate Systems
in Astronomy  Next→
 TOC ↑