 must be contained within
                  a right circular cone of angular radius less
                  than (pi/2) - SPICE_GF_MARGIN radians; in other
                  words, there must be a vector A such that all
                  boundary vectors have angular separation from
                  A of less than (pi/2)-SPICE_GF_MARGIN radians.

                  2) There must be a pair of boundary vectors U, V
                  such that all other boundary vectors lie in
                  the same half sp