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Description:
This function returns the geometric parameters describing
the supplied ellipse.
Synopsis
void astEllipsePars( AstEllipse
$\ast $this, double
centre[2], double $\ast $a,
double $\ast $b,
double $\ast $angle,
double p1[2], double p2[2] )
Parameters:
this
centre
The coordinates of the
Ellipse centre are returned in this arrays.
a
Returned holding the halflength of the first axis of the ellipse.
b
Returned holding the halflength of the second axis of the ellipse.
angle
If
the coordinate system in which the Ellipse is defined has axes (X,Y), then "
$\ast $angle"
is returned holding the angle from the positive direction of the Y axis to the first
axis of the ellipse, in radians. Positive rotation is in the same sense as rotation
from the positive direction of Y to the positive direction of X.
p1
An array in
which to return the coordinates at one of the two ends of the first axis of the
ellipse. A NULL pointer can be supplied if these coordinates are not needed.
p2
An
array in which to return the coordinates at one of the two ends of the second axis of
the ellipse. A NULL pointer can be supplied if these coordinates are not needed.
Notes:

If the coordinate system represented by the Ellipse has been changed since it was first
created, the returned parameters refer to the new (changed) coordinate system, rather
than the original coordinate system. Note however that if the transformation from
original to new coordinate system is nonlinear, the shape represented by the supplied
Ellipse object may not be an accurate ellipse.

Values of AST__BAD are returned for the parameters without error if the ellipse is
degenerate or undefined.
Copyright (C) 2019 East Asian Observatory
 ←Prev
 AST
A Library for Handling
World
Coordinate Systems
in Astronomy  Next→
 TOC ↑