                        xvec = spoint - obspos

                         The components of 'obspos' are given in units of km.

               found     the logical flag indicating whether or not the ray
                         intersects the target.  If an intersection exists
                         'found' will be returned as true. If the ray misses
                         the target, 'found' will return as false.

                         [1,1] = size(surf(i).found)
                         logical = c