Figure 2
Schematic diagram of the circle centre determination. Elliptical projection Π of the real imaged circle K r and imaginary circle K i on the XY-image plane with correspondent centres in c r and c i , |AB| = 2a, |CD| = 2b, ∠ABA' = ∠BAB' = γ, the distance between the projection centre O and the XY-plane is equal to d. The bisecting line of the cone with the basis Π on the XY-plane and the top in the perspective projection centre O coincided with the Z-axis. See the text for explanation.