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New perspectives to save cultural heritage
Altan, M. Orhan

Ch. Ioannidis, Maria Tsakiri
School of Rural and Surveying Engineering, National Technical University of Athens, Greece
(email: cioannid@survey.ntua.gr, mtsakiri@central.ntua.gr)
KEYWORDS: Cultural Heritage, Laser Scanning, Modelling, Archaeology, Close range photogrammetry, Monuments in seismic
areas, Data capture, Statue
Cultural heritage applications involve measurements at different possible scales. While photogrammetry and metric surveying
techniques can be suitable for archaeological sites and buildings, they present certain disadvantages for smaller and more complex
objects such as statues. Laser scanning technology with its automated data capture capabilities is bringing new perspectives and can
satisfy most requirements of this type of applications. This paper describes a practical example based on the combined use of digital
photogrammetry and laser scanning techniques with an aim to create a geometrically accurate 3D model of the ancient statue of
Hermes of Praxiteles, which is housed in the archaeological museum of Olympia in Greece. A comparative evaluation of the two
techniques in the data capture and modelling of the statue is discussed and typical results of the models are presented.
Throughout 20 th century, photogrammetry has almost been the
exclusive technique implemented for the geometric recording
and documentation of large monuments and complex irregular
structures, such as statues. Sensitive and fragile objects,
consisting of a variety of surfaces usually with many curves and
holes, could be restituted in analog or digital 3D form through
photographic imaging as a non-contact method. However, the
restrictions of stereoscopic photography in combination with
the complexity of the object, poses several limitations for the
detailed recording of objects, which in an indirect way can also
affect the obtained accuracy.
The recent advances in terrestrial 3D laser scanning have
indicated that this technique has the potential to serve as a
powerful tool for architectural and archaeological recording.
The advantages manifest specifically for the recording of
complex objects, such as sculptures and statues. Examples of
applications using laser scanning techniques with encouraging
results are found in Adolfsson (1997), Beraldin et al. (2000),
Levoy et al. (£000), Rocchini et al. (2001), Henz (2002).
Terrestrial scanners may be categorized into two groups:
• Triangulation scanners, which consist of a laser and a CCD
housed in a single unit. The CCD is used to record the
displacement of a stripe of laser light projected onto an
object. Usually the seamier to object distance is less than 2m
(close-range scanners). This type of scanners has geometrical
resolution and accuracy better than 1mm. •
• Time of flight scanners (terrestrial LIDAR), which use a
pulsed laser to measure the range to a point on an object’s
surface. There are several manufacturers who currently
provide scanners of this type, like Cyra Technologies,
Callidus Precision systems, MENSI, Riegl Laser
Measurement Systems, Zolleral Froehlich etc, which have
range distance between 2-100 m and resolution of few mm
(Kern, 2001). These systems do not provide satisfactory
accuracies for applications requiring recording of complex
monuments. In addition, the speed of data acquisition is
much slower compared to the triangulation scanners.
The development of varying types of scanners cannot imply
that the 3D documentation of sizeable and complex objects,
such as large statues, has become trivial or that scanning can
replace all other imaging techniques. On the contrary, there are
several technical difficulties associated with the use of
scanning, such as data management due to the huge quantities
of data generated on-site, and requirements for sophisticated
processing capable of performing registration and merging of
large numbers of scans. Furthermore, the type and format of the
products generated by scanning techniques, such as point
clouds, triangle meshes and 3D models, are different to those
usually expected or are familiar with by the end users like
architects, archaeologists or conservators.
Figure 1. The Hermes statue as is exhibited in the museum