main/src/georegression/geometry/UtilEllipse_F64.java
public static double evaluate( double x , double y , EllipseRotated_F64 ellipse ) {

		double cphi = Math.cos(ellipse.phi);
		double sphi = Math.sin(ellipse.phi);

		x -= ellipse.center.x;
		y -= ellipse.center.y;

		double left = (x*cphi + y*sphi);
		double right = (-x*sphi + y*cphi);

		double ll = left/ellipse.a;
		double rr = right/ellipse.b;

		return ll*ll + rr*rr;
	}
public static double evaluate( double x , double y , EllipseRotated_F64 ellipse ) {

		double cphi = Math.cos(ellipse.phi);
		double sphi = Math.sin(ellipse.phi);

		x -= ellipse.center.x;
		y -= ellipse.center.y;

		double left = (x*cphi + y*sphi);
		double right = (-x*sphi + y*cphi);

		double ll = left/ellipse.a;
		double rr = right/ellipse.b;

		return ll*ll + rr*rr;
	}
Computes the value of the quadratic ellipse function at point (x,y).  Should equal 1 if the point is on the
ellipse.
@param x x-coordinate
@param y y-coordinate
@param ellipse Ellipse equation being evaluated.
@return value of ellipse equation at point (x,y)