/** Returns the curvature of the ellipse arc. Curvature is negative if the arc is indirect. */
public double curvature(double t) {
// convert position to angle
if (angleExtent < 0) t = startAngle - t;
else t = startAngle + t;
double kappa = ellipse.curvature(t);
return this.isDirect() ? kappa : -kappa;
}
