Fig.19
the total strength of the line is dependent of L1(x,y)+L2(x,y)+L3(x,y)+ L4(y).
Fig.20
The analysis of figure 20 is similar to the one done in figure 19, but the lines taken into
account in figure 21 are at the opposite sites of the ones taken into account in figure 20, so
the x components steer the resultant line to the left of the central line as is seen in figure 20
and is dependent of L7(x,y) + L6(x,y) + L5(x,y) + L4(y).
Fig.21