The rho dimension of a conic arc PQ defines the shape of the conic. The line segments PR and QR are tangent to the ellipse at points P and Q respectively. The line segment RD intersects the line segment PQ at point D. Here, D is the mid point of the line segment PQ. The rho dimension specifies a ratio along a vector from the chord (PQ) through a point C to the vertex (R). Point C is at the maximum distance (CD), measured by a normal from the chord PQ to the conic segment PQ.