Figure 11
(a)-(b) Projection Method 1: from a node 
in 3D space to a node 
on the 3D sphere. There are two cases for the calculation of spherical distance 
: (a) 
and 
are different points on the sphere; (b) 
and 
are the same point on the sphere. (c) Projection Method 2—Stereographic Projection: an one-to-one mapping from a node 
in a 3D hyperplane to a node 
on a 4D sphere.