the definition.

               [1,1] = size(emissn); double = class(emissn)

      visibl   is a logical flag indicating whether the surface
               point is visible to the observer. `visibl' takes into
               account whether the target surface occults `spoint',
               regardless of the emission angle at `spoint'. `visibl' is
               returned with the value true if `spoint' is visible;
               otherwise it is false.

               [1,1] = size(visibl); logical = class(