CIPA 2005 XX International Symposium, 26 September - 01 October, 2005, Torino, Italy 
896 
SEGMENTATION AND FILTERING OF 
LASER SCANNER DATA FOR CULTURAL HERITAGE 
J.L Lerma, J.M Biosca 
ETSI Geodésica, Cartográfica y Topográfica. Universidad Politécnica de Valencia. - C° de Vera, s/n. 46022, Valencia (Spain) 
jllerma@cgf.upv.es, jobiota@topo.upv.es 
KEY WORDS: Laser Scanner, segmentation, filtering, 3D modelling 
ABSTRACT 
The use of terrestrial laser scanners is increasing in the field of cultural heritage recording due to their high data acquisition rate, 
relatively high accuracy and high spatial data density. The main problem related to this new technique is the treatment of the 
collected data. 
This paper describes an automatic approach in laser scanning point clouds for architectural modelling. The aim of the algorithm is to 
obtain real surfaces of the scanned object and reduce the data volume. For that purpose, our algorithm extracts automatically all the 
planar surfaces of the monument, including the vertical ones, and filters out non-relevant points. The surfaces consist of groups of 
points. Obtaining its bounds we can eliminate all the original points that form the surfaces leading to a better representation of the 
object and the reduction of the data volume. The algorithm bounds the surfaces regardless the planar orientation and shapes. This is 
performed by three different techniques according to the shape of the surface: intersection of planar surfaces, the Hough transform 
and a new method based on the projection of the surfaces into accumulator tables. 
The algorithm has been tested in a Baroque monument placed in the city centre of Valencia. For that purpose, the measurement 
included the four outer façades and was carried out from three stations, lasting three hours. The results of the test are presented in this 
paper. 
1. INTRODUCTION 
The use of terrestrial laser scanners is increasing in the field of 
cultural heritage. Because of their high data acquisition rate, 
relatively high accuracy and high spatial data density, laser 
scanners are being used for several applications like 
documentation of historic monuments or virtual visualizations. 
Nevertheless, the laser scanner data has some problems. The 
first problem is the huge amount of data. The point cloud of a 
monument easily contains more than one million of measured 
points. Such an amount of data causes problems on CAD 
software. In addition, some of the measured points are 
erroneous. Errors origin is multiple: systematic instrumental 
errors; and partial reflection of the laser spot at edges. 
Additionally, the collection of massive point clouds requires 
further filtering for non-relevant features, e.g. moving objects 
such as people or birds. Besides, the absence of semantic 
information within the laser scanning point clouds makes 
difficult the object interpretation. 
Some authors have combined laser scanner data and 
photogrammetry in cultural heritage recording (Heinz, 2002; 
Briese et al., 2003; Boehler et al., 2003; Ioannidis, et al., 2003; 
Drap et al, 2003). Others have used different techniques to treat 
laser data only. Some of the techniques are focus on the object 
segmentation of architectural facades (Bomaz et al, 2003; 
Biosca, 2005). 
In order to solve the above mentioned problems, we present an 
approach to obtain real surfaces from a scanned object, on the 
one hand, and a reduction of the data volume, on the other. The 
algorithm is based on clustering techniques and manages to 
extract planar surfaces, including vertical ones, and filters out 
non-relevant points. Once we have the planar surfaces of the 
monument, several methods are proposed to extract feature 
bounds. 
This algorithm has been tested in a Baroque monument placed 
in the city centre of Valencia, the Marques de Dos Aguas 
palace. 
The paper will be organized as follows. Section 2 gives a 
description of the study site. Section 3 presents the acquisition 
of laser scanner data in the study site. Section 4 covers the 
algorithm developed. Section 5 provides the results of the study 
and a discussion. Finally, section 6 summarizes the main 
achievements reached in this work. 
2. STUDY SITE 
The Marques de Dos Aguas palace is a Baroque building placed 
in the Valencia city centre. The initial house was built in the 
15 lh century by one of the most prestigious families of that 
period. The palace is the result of a radical restyle performed in 
the 1740s. 
The current building is composed by two levels more than the 
ground floor and is 20 metres high. It has three towers in the 
comers that arise 28 metres high. 
The main door was adorned with a scene made of alabaster 
where two big human figures stand out at the sides representing 
the two main rivers of the region. 
The façade was decorated with frescoes but in 1867 were 
replaced by grey and pink stuccos imitating marble stones. At 
the same time balconies of French style were added. 
Nowadays, the palace is property of the Spanish authority and 
the National Ceramic Museum is located therein. 
3. LASER SCANNING SURVEY 
Laser scanning survey was made with a MENSI GS100 laser 
scanner. It is a hybrid time-of-flight laser scanner with a 
maximum range of 100 metres. The survey was carried out from 
three different stations and took up three hours. Figure 1 shows 
the position and field of view of each station.