490
Object segmentation in cultural heritage
Leandro Bomaz(*), Fulvio Rinaudo (*), Marco Roggero (*)
(*) Politecnico di Torino - Dipartimento di Georisorse e Territorio
C.so Duca degli Abruzzi, 24- 10129 TORINO
Tel.+39.011.564.7687/7659/ 0161226390 Fax.+39.011.564.7699
E-mail: bornaz@polito.it; fulvio.rinaudo@polito.it; roggero@atlantic.polito.it:
KEY WORDS: Remote sensing, Cultural heritage, Analysis, Close Range, Interpretation, Architectural Heritage, Laser scanning,
Segmentation.
ABSTRACTS:
With the introduction of new terrestrial laser scanning technologies it is possible to obtain a “dense DTM” of any cultural heritage
object in a very quickly and fast way. The 3D model acquired with laser devices represents a dense point cloud of the object. In the
case of very complex 3D models it is not easy to manually directly derive a correct surface reproduction of the object from the model
in a simple and correct way.
A valid aid in the modelling of objects is the segmentation technique. This allows on different layers portions of point clouds that
have similar geometric ownerships to be organised it.
The following article shows the results of some segmentation techniques applied to the case of architectural survey. The advantages
and the disadvantages of every methodology are put in evidence.
1. INTRODUCTION
1.1 Introduction
Recently new instruments have been introduced in the field
of surveying that are able to survey portions of land and
objects of various shapes and sizes in a quick and cheap
manner. These instruments, based on laser technology, are
commonly known as laser scanners.
Laser scanners can be considered as highly automated total
stations. They are usually made up of a laser that has been
optimised for high velocity surveying and of a set of
mechanisms that allows the laser radius to be directed in
space in a range that varies according to the instrument that is
being used.
The laser scanner therefore allows millions of points to be
recorded in a short time.
Because of their practicality and versatility, these kinds of
instruments are today widely used in the field of
archaeological surveying.
1.2 Why segment?
The digital models obtained from laser scanners are nothing
more than dense point clouds (DDEM- Dense Digital
Elevation Model). These point clouds are often remarkably
complex. This occurs above all in the case of archaeological
surveying of monuments and historical buildings in which
there is a great variability of the structure.
After having acquired any object with the laser technique, the
usual aim is that of obtaining the greatest amount of
geometric information from the model itself in the easiest and
most automatic way.
Research today is often dedicated to this new field and many
treatment and management procedures of laser data have
been developed.
One of the stages in which it is necessary to do further
research is modelling. By modelling we mean passing from a
point model, as obtained with the laser sensors, to a surface
model. It is in fact possible to automatically extract sections
or level curves from the object, carry out numerical analysis
or even integrate the model with digital images to create a
coloured 3D model or to produce an orthophoto.
Figure 1 - A DDEM obtained using a RIEGL LMS Z210
laser scanner - Piazza San Marco- Venice - Italy
The solid modelling is easily obtained if the model that has
been surveyed with a lqser scanner has a simple geometry
(for example, a bas-relief or a uniform façade without
balconies or high parts protruding), but can become very
