The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Voi. XXXVII. Part B5. Beijing 2008 
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along the facade and one on either side. Four Ionic columns on 
a high stylobate, with metal railings between them, adorned the 
west facade. Finally, another door on the south facade of the 
western temple opened onto the porch of the Karyatides 
(Maidens porch), a pi-shaped structure with six female statues, 
each different, instead of columns to support the roof. Five of 
them are in the Acropolis Museum and another in the British 
Museum; those at the building are copies. The temple burned in 
the first century BC and was subsequently repaired with minor 
alterations. In the Early Christian period, it was converted into a 
church. It became palace under Frankish rule and the residence 
of the Turkish commander's harem in the Ottoman period. In 
the early nineteenth century, Lord Elgin removed one of the 
Karyatides and a column and during the Greek War of 
Independence the building was bombarded and severely 
damaged. Restoration was undertaken immediately after the end 
of the war and again in 1979-1987, when the Erechtheion 
became the first monument of the Acropolis to be restored. 
Figure 1. Different views of the Erechtheion. (a) South side with the porch of the Karyatides seen from the top of the Parthenon, (b) 
East and (c) North sides with the ionic columns, (d) West side with its (natural and “unnatural”) occlusions. 
1.2 Previous work 
Some of the Acropolis of Athens large monuments have been 
surveyed and modeled already in previous research work. The 
most impressive results were presented in the computer 
animation movie The Parthenon, where all the different parts of 
the monument, spread in various museums and countries for 
over two centuries, were virtually reunited (Stumpfel et al., 
2003; Debevec, 2005). The models were created using laser 
scanners, structured light systems, photogrammetry and 
photometric stereo and rendered with inverse global 
illuminations. Lundgren (2004) conducted a project on 
digitising the Parthenon with a laser scanner at 1.2 cm 
resolution. For the Erechtheion, different studies were carried 
out. Blomerus and Lesk (2007) presented an AutoCAD-based 
4D model of the entire monument. The model was based on 
paintings, drawing and old photos. 
2. PROCEDURES AND REQUIREMENTS 
IN 3D MODELING 
Nowadays, 3D modeling of objects and sites is generally 
performed by means of images or active sensors (like laser 
scanner or structured light projectors), depending on the surface 
characteristics, required accuracy, object dimensions and 
location, etc. Active sensors (Blais, 2004) provide directly 3D 
data. Active sensors, combined with color information, either 
from the sensor itself or from a digital camera, can capture 
relatively accurate geometric details, but they remain costly, 
usually bulky, not easy to use, require stable platform and are 
influenced by surface properties. They have limited flexibility, 
since a range sensor is intended for a specific range and volume. 
They may acquire millions of points, even on perfectly flat 
surfaces, often resulting in over-sampling, but it is likely that 
comers and edged are not well captured.