def to_s
      str = "Polyline["
      vertices.each do |vertex|
        str += vertex.to_element_s + ", "
      end
      str.slice!(str.length - 2, 2) if(vertices.size > 0)
      str += "] "
      str += "open" if(@is_open)
      str += "closed" if(!@is_open)
      return str
    end
def to_s
      str = "Polyline["
      vertices.each do |vertex|
        str += vertex.to_element_s + ", "
      end
      str.slice!(str.length - 2, 2) if(vertices.size > 0)
      str += "] "
      str += "open" if(@is_open)
      str += "closed" if(!@is_open)
      return str
    end
[Input]
  _rhs_ is Polyline.
 [Output]
  return true if rhs equals myself.