Calculating a point on an ellipse

Question

Say I have two points A and B positioned on the circumference of an ellipse, and they form an angle X from the center point. Now say that point A is moved to a new point C. How can I calculate the new point for B such that the angle X remains constant? Pointers to code of some kind would be appreciated.

Answer 1

Why not use the polar form of an ellipse where the angle is measured from the ellipse centre??? http://en.wikipedia.org/wiki/Ellipse#Polar_form_relative_to_center From this equation, if you know the value of the angle between A and B (say theta), and you know the value of central angle of the new point C (say phi), then your required point D can be calculated from this polar form using an angle (theta + phi)