def edges
      edge_ary = Array.new(4)
      edge_ary[0] = FiniteLine.new( base_point, base_point+u_vector)
      edge_ary[1] = FiniteLine.new( base_point+u_vector, base_point+u_vector+v_vector)
      edge_ary[2] = FiniteLine.new( base_point+u_vector+v_vector, base_point+v_vector)
      edge_ary[3] = FiniteLine.new( base_point+v_vector, base_point)
      return edge_ary
    end
def edges
      edge_ary = Array.new(4)
      edge_ary[0] = FiniteLine.new( base_point, base_point+u_vector)
      edge_ary[1] = FiniteLine.new( base_point+u_vector, base_point+u_vector+v_vector)
      edge_ary[2] = FiniteLine.new( base_point+u_vector+v_vector, base_point+v_vector)
      edge_ary[3] = FiniteLine.new( base_point+v_vector, base_point)
      return edge_ary
    end
[Output]
  return edges of rectangle as Array of FiniteLine.