Structs
Cap represents a disc-shaped region defined by a center and radius.
Technically this shape is called a “spherical cap” (rather than disc)
because it is not planar; the cap represents a portion of the sphere that
has been cut off by a plane. The boundary of the cap is the circle defined
by the intersection of the sphere and the plane. For containment purposes,
the cap is a closed set, i.e. it contains its boundary.