ace bounded by the plane
                  containing U and V. Furthermore, all other
                  boundary vectors must have orthogonal
                  projections onto a plane normal to this plane
                  such that the projections have angular
                  separation of at least 2*SPICE_GF_MARGIN radians
                  from the plane spanned by U and V.

      Arguments-

      inst     the string naming the instrument, such as a
               spacecraft-mounted framing camera, t