code: public Coordinate getMiddlePoint() {
  		double x = this.x1() + 0.5 * (this.x2() - this.x1());
  		double y = this.y1() + 0.5 * (this.y2() - this.y1());
  		return new Coordinate(x, y);
  	}
docs: Return the middle point of this linesegment.