question: public ShapeTileBox bounding_box ( ) { if ( bounding_box != null ) return bounding_box ; PlaPointFloat start_corner = start_point_approx ( ) ; PlaPointFloat end_corner = end_point_approx ( ) ; double llx = Math . min ( start_corner . v_x , end_corner . v_x ) ; double lly = Math . min ( start_corner . v_y , end_corner . v_y ) ; double urx = Math . max ( start_corner . v_x , end_corner . v_x ) ; double ury = Math . max ( start_corner . v_y , end_corner . v_y ) ; PlaPointInt lower_left = new PlaPointInt ( Math . floor ( llx ) , Math . floor ( lly ) ) ; PlaPointInt upper_right = new PlaPointInt ( Math . ceil ( urx ) , Math . ceil ( ury ) ) ; bounding_box = new ShapeTileBox ( lower_left , upper_right ) ; return bounding_box ; }
target:  calculates the smallest surrounding box of this line segmant