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Figure 2 Conceptual circle that best fits an ellipse. An ellipse (red line) can be constructed by drawing two concentric circles (black lines): the radius of the inscribed circle defines the semi-minor axis (b), whereas the radius of the circumscribed circle defines the semi-major axis (a). From c and p values, the radius (r) of the circle that intersects the ellipse in its semi-latus rectum (blue line) can be computed.