import numpy as np
__all__ = ['get_ellipse_points']
[docs]
def get_ellipse_points(theta, equatorial_radius, oblateness=0.0, center_f=0.0, center_g=0.0,
position_angle=0.0):
"""Calculate points on an ellipse for the given input parameters.
Parameters
----------
theta : `float`, array-like
Angular coordinate, in radians, where the ellipse points are
calculated.
equatorial_radius : `float`, `int`
Semi-major axis of the ellipse, in km.
oblateness : `float`, `int`, optional
Oblateness of the ellipse.
center_f : `float`, `int`, optional
Coordinate of the ellipse center in the f direction, in km.
center_g : `float`, `int`, optional
Coordinate of the ellipse center in the g direction, in km.
position_angle : `float`, `int`, optional
The pole position angle of the ellipse in degrees.
Zero is in the North direction ('g-positive'). Positive clockwise.
Returns
-------
x_model : `float`, `numpy.array`
Cartesian x-component, in km.
y_model : `float`, `numpy.array`
Cartesian y-component, in km.
r_model : `float`, `numpy.array`
Radial distance, in km.
theta : `float`, array-like
Input angular coordinate, in radians.
"""
a = equatorial_radius
b = equatorial_radius - equatorial_radius * oblateness
phi = position_angle * (np.pi / 180.0)
ang = theta + phi
r_model = (a * b) / np.sqrt((a * np.sin(ang)) ** 2 + (b * np.cos(ang)) ** 2)
x_model = r_model * np.cos(theta) + center_f
y_model = r_model * np.sin(theta) + center_g
return x_model, y_model, r_model, theta