def contains_point(x,y,z)
      behind = true
      @planes.each{|p|
        behind = (0 >= p.distance_to_point(x,y,z))
        break if not behind
      }
      return behind
    end
def contains_point(x,y,z)
      behind = true
      @planes.each{|p|
        behind = (0 >= p.distance_to_point(x,y,z))
        break if not behind
      }
      return behind
    end
A volume contains a point if it lies behind all the planes