Algorithm 1: Pseudo-code of the swapping process between the old and new reference lines.
1:	Setting: sort the previous lines in descending order according to their length
2:	For each previous line from long to short
3:	If this line has matching line in the current scan and composes from number of points more than threshold
4:	calculate the unit vector of this line (1st reference)
5:	for each previous rest line from long to short
6:	If this line has matching line in the current scan and composes from number of points more than threshold
7:	calculate the unit vector of this line (2nd reference)
8:	calculate the intersected angle between the two vectors
9:	If angle > 90
10:	angle = 180−angle
11:	End if
12:	If absolute angle > threshold
13:	swap the two old reference lines with the new ones
14:	raise flag
15:	End if
16:	End if
17:	End for
18:	End if
19:	End for