Full text: Mapping without the sun

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INVESTIGATING SEVERAL POINT CLOUD REGISTRATION MOTHEDS 
Luo Dean 1 , Zhou Keqin 1 , Huang Jizhong 2 
1 Dept, of Surveying and Mapping, Beijing University of Civil Engineering and Architecture, No.l Zhanlanguan Road, 
Xicheng District, Beijing, PRC - (Luodean, Zhoukeqin)@bucea.edu.cn 
2 Yungang Grottoes Research institute, Yungang town, Shanxi Datong, PRC-Zhjizhong@yahoo.com.cn 
KEY WORDS: 3D Point Cloud, Registration, Accuracy, Terrestrial Laser Scanner 
ABSTRACT: 
Terrestrial laser scanner (TLS) technology is widely used for 3D reconstruction and modelling in the field of heritage recording. For 
any object of complex geometry, multiple scans are typically required to generate a 3D model. In order to get a whole 3D model, it’s 
necessary to transform the scan data from the sensor's local coordinate system into a uniform Cartesian reference datum, and the core 
task is point cloud registration. Today, various ways are available to register point clouds to each other, they are: ©Populating a 
survey network with scans,© Direct merging of scans with each other,© “Cloud-to-cloud” registration, and have different 
characteristics and different work styles. Based on the point clouds captured for YUNGANG Grottoes, the above three registration 
methods are employed to merge multiple scans into a uniform reference datum. Three different registration procedures, data 
matching accuracy, and test results are described in details. By comparing and analysing to the three registration results, the most 
suitable way is found to meet our work. 
1. INTRODUCTION 
Terrestrial laser scanners (TLSs) have found application to 
many measurement tasks, particularly for cultural heritage 
recording. Their high resolution, accurate and rapid point cloud 
capture capabilities allow cost effective production of digital 
documentation of cultural heritage features. In fact, this 
technology may entail any task from the digital preservation of 
historic and culturally significant structures to mapping 
archaeological dig sites. Laser scanning for cultural heritage 
recording is increasing in popularity. There are numerous 
scoping papers in which authors discuss the potential of TLS 
for cultural heritage recording and report research findings 
(Boehler et al. 2002; Bomaz et al. 2003; El-Hakim et al. 200). 
For any cultural heritage recording project, field data captured 
work is easy to be done by TLS, but a series of laborious works 
have to be done one by one in order to get the object 3D 
models. In most cases, single scan is not enough to reconstruct 
the object 3D model, the object has to be scanned from 
different viewpoints in order to completely reconstruct its 3D 
model. Because each scan has its own local coordinate system, 
all the local point clouds must be transformed into a common 
coordinate system. This procedure is usually referred as 
registration. The registration of point clouds is an essential task 
in TLS applications. 
Based on the point clouds captured for YUNGANG Grottoes, 
three registration methods are employed to merge multiple 
scans into a uniform reference datum. Three different 
registration procedures, data matching accuracy, and test 
results are described in details. By comparing and analysing to 
the three registration results, the most suitable way is found to 
meet our work. 
This paper introduces our research background firstly. Section 
2 briefly lists the main registration methods, and discusses their 
merits and demerits. Section 3 describes three different 
registration procedures for the point clouds captured for 
YUNGANG Grottoes. Section 4 comparing the three 
registration results in details, and the most suitable way is 
found to meet our work. Finally, Section 5 gives the 
conclusions and some proposals for the same works. 
2. BACKGROUND 
Yungang Grottoes is the model of the culture’s compromising 
between China and Western and the spirit of the eastern stone 
carving art. It is located in Yungang town 16km from Datong, 
and was firstly carved 1500 years ago (in A.D. 460). The 
Yungang Grottoes were carved on the face of a low ridge, 
stretching 1km from east to west; there are 254 caves and some 
51,000 statues. It is one of the most extensive grottoes in China, 
covering approximately 18,000m 2 . 
In order to preserve and utilize the culture heritage resources 
better, Yungang Grottoes Research Institute and our college 
worked together to find the suitable way to construct grottoes’ 
digital documents. After analysing and comparing to existent 
survey technologies TLS was employed to do the job. In order 
to assure it feasible and productive some grottoes were selected 
to do a test. The relative field data captured works had been 
done, the successive data processing works began on May 2007. 
3. REGISTRATION METHODS REVIEW 
Today, various ways are available to register point clouds to 
each other. In general these ways can be classified three basic 
methods according to their work styles (Geoff Jacobs, 2005). 
Each of them is described below in detail. 
3.1 Method 1: Populating a survey network with scans 
This registration methodology is the one most likely to 
traditional surveying. A control network is established firstly 
and then each individual scan is tied to the control network as 
an independent task. The scans are registered “to each other” 
only in a relative sense, based on how well each scan is 
individually tied to the control network. If one scan is not tied
	        
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