1-1-7 
views. Item names in both table are equvilient to the 
address in section 2. Formulae defining the items are also 
listed for reference. 
Set 7° to the transformation obtained in coarse 
matching. Strength of each matched line segment pair 
under T° is shown in Table 4. A minus volume tells the 
strength is invalid. The strength is measured when given a 
threshold (=0.1 degree) as rotation step. Adjustment to 
7° is the weighed average of the strengths in matched 
line segment pairs (Table 5). Adjustment in each iteration 
is decided by strength analysis if it can also minify the 
distance measure between two views. Figure 5 shows the 
change of distance measure in fine adjustment and the 
method used to decide the adjustment in each iteration. It 
is obvious that strength analysis is valid in most of the 
case. Adjustment by strength analysis is efficient, as it 
requires 250 milliseconds in each iteration, while testing 
all the possible adjustment to find the best one requires 
8150 milliseconds in average. Figure 6 shows the change 
of strength in each matched line segment pair in fine 
adjustment. From global viewpoint, the strength total is 
reduced during fine adjustment. 
Accuracy in Z-lmage matching is examined by comparing 
the matching result with the ground truth of manually 
measured data. The estimation error in shift vector is 
examined using the distance between two view points, 
while rotation angle is examined using the angle between 
x-axis of two sensors’ coordinate system. Estimation error 
in shift vector is about 1.43m by coarse match, and about 
0.04m after fine adjustment. Estimation error in rotation 
angle has not a lot change before and after fine 
adjustment. After adjustment, estimation error in rotation 
angle is about 0.1 degree. Figure 7 shows the change of 
estimation error in fine adjustment process. 
Figure 8 shows the result in matching ground points to 
track the translation parameter along Z-axis. Accuracy in 
matching has an accuracy of 0.2m. Error comes major 
from inaccurate interpolation of ground points. 
Improvement in accuracy has to be addressed in future 
study. Figure 9 shows the final result. 
Table 1. Reliability evaluation of the line segments 
extracted in two views “o n ’’and “o d ” stand for the 
reliability of parameter estimation of line normal and 
orthogonal distance. “Var.” and “Length” are the 
regression variance and length of the line segment. “Point 
Number” is the number of image points used in the line 
parameter estimation. 
View 1 
Line No. 
<7„ 
(°) 
(pixel) 
Var. 
(pixel) 
Length 
(pixel) 
Point 
Number 
0 
0.08 
0.502 
1.043 
83 
1362 
1 
0.066 
0.452 
1.441 
169 
899 
2 
0.126 
0.635 
1.05 
78 
561 
3 
0.168 
0.86 
1.7 
101 
453 
4 
0.93 
1.82 
0.882 
16 
202 
5 
0.471 
2.723 
0.253 
25 
20 
6 
2.221 
6.23 
2.094 
43 
19 
7 
4.097 
9.875 
1.338 
47 
43 
Table 2. Major items in distance measurement after 
coarse matching 
Items 
Sub-Items 
Formulae & 
Explanation 
Result 
/,(Z) 2 ID.) 
EQ.7 
105098.1 
W Px) 
EQ.8 
73909.53 
N total 
Total point 
number 
12062 
Matched 
number EQ.13 
11155 
EQ.11 
59397 
I „(Pol) 
EQ.9 
14512 
M* 2 i*.) 
EQ.14 
31188.54 
/*(4 I M 
EQ.16 
28933 
EQ.15 
2256 
Table 3. Conditional information between matched line relation pairs after coarse matching 
Matched 
Pair 
(j,i) 
angle(n), nf ) 
dis(d l j,df) 
&jij 
N‘ 
in 
N‘ 
' out 
rf 
EQ.17 
EQ.18 
EQ.17 
EQ.18 
Matched point 
number 
Unmatched 
point number 
EQ.16 
EQ.19 
(2,0) 
0.178 
2.853 
0.132 
0.682 
1672 
142 
10731 
29024 
(0,1) 
1.07 
2.685 
0.102 
0.675 
1234 
3 
7799 
19792 
(3,2) 
1.014 
2.423 
0.184 
0.977 
729 
130 
5442 
13744 
(1,3) 
0.178 
2.159 
0.12 
0.862 
756 
11 
4774 
12272 
(5,5) 
1.922 
3.722 
0.587 
3.584 
19 
3 
186 
352