of E g is conducted in a hill climbing method. 
Table 1. Line segment extraction is conducted using the Z- 
Image without ground points. From Table 1, it is obvious 
that line extraction of #0~#4 in both views has rather high 
reliability, while #6,#7 in viewl and #4,#6,#8,#9 in view2 
are wrong extractions. In Table 1, we can find unreliable 
line segments always have larger values on o n or g d 
than reliable ones, whereas there’s no obvious difference 
in regression variance between good and poor extractions. 
This means o n and o d has better performance in 
characterizing the reliability of line parameter estimation. 
Figure 3. Parameters that are involved in multiple views’ 
registration, v., v and v k stand for the viewpoints of 
view #/, view #j and view #k. d ij is the distances between 
V i and v . p is the angles from vy k to VVj. e u 
is the angle from X-axis of view #i’s coordinate system to 
V.V , a. is the angle from the X-axis of view #i’s 
coordinate system to view #j’s. 
4 EXPERIMENT RESULT AND DISCUSSION 
In this section, we will discuss two sets of experiment 
results. First, we will tabulate some of the results obtained 
in registering two views of laser range image using Z- 
Image to testify the méthodologie framework for pair-wise 
registration. Secondly, we will discuss an experiment 
where 29 views of overlapping laser range images are 
registered to construct a spatial model for the buildings in 
IIS, Univ. of Tokyo. The experiment aims at examine 
robustness of pair-wise registration, and testifying the 
efficiency of the method in solving the error accumulation 
problem. Laser range images used in the experiment are 
measured with the range of 360° in horizontal rotation 
and 60° in vertical rotation, with the resolution of 2 sample 
per horizontal degree and 1 sample per vertical degree. 
Laser range measurement has an accuracy of ±5cm. In 
order to examine the registration accuracy, each view 
point has been measured manually using GPS. It has an 
accuracy of ±10cm. 
4.1 Experiment of registering two views of laser range 
image 
Figure 4 shows two views of laser range image, and the 
Z-lmages generated with a resolution of 0.25m/pixel. 
Reliability evaluation of line segments in view 1 is listed in 
(a) view 1 
Sf.- a'v .3 
1 / •- - . 
w 
(b) view 2 
Figure 4 Two views of laser range image and their Z- 
Images. Left figures are laser range images shown in 3D 
space, while right figures are the Z-lmages generated. 
Line segments extracted are shown in left figures. 
Characters stand for the sequential numbers. 
In coarse matching, given a threshold (=2°) for the 
maximum difference in intersection angle, a threshold 
(=2pixel) for the maximum difference in distance, there are 
totally 48 candidates obtained. All candidates are tried to 
match the views. The one composed by Line segment 
pairs (#2,#1) of viewl and (#0,#3) of view2 which yields 
minimum distance measure is selected as the optimum. 
To understand the distance measure defined in this 
research, Table 2 and Table 3 list the results of some 
major items when using the above candidate to match two 
1-1-6