def add_line(self, p1, p2, char_length):
        """
        Add a line to the list. Check if the nodes already exist, and add them
        if not.

        Return the line index (1-indixed, starting with 1)
        """
        p1_id = self.get_point_id(p1, char_length)
        p2_id = self.get_point_id(p2, char_length)
        self.Lines.append((p1_id, p2_id))
        return len(self.Lines)
Add a line to the list. Check if the nodes already exist, and add them
        if not.

        Return the line index (1-indixed, starting with 1)