Figure 3.

Definition of unit sphere and projection of the unit sphere into a specific planar grid. (a) Reconstructed mesh with unit sphere located at the center of the acetabulum (see Figure 1(d)). (b) Initial unit sphere in three dimensions, with ray (red line) from center point (black) to grid point (red). (c) Planar grid representation, with the example grid point highlighted (red) ($\vec{n}$: acetabular axis, see Figure 1(e), θ  and  φ according to formulas (1) to (2).)