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This paper presents preliminary results on the development of a 3D audiovisual model of the Anta Pintada (painted
dolmen) of Antelas, a Neolithic chamber tomb located in Oliveira de Frades and listed as Portuguese national
monument. The final aim of the project is to create a highly accurate Virtual Reality (VR) model of this unique
archaeological site, capable of providing not only visual but also acoustic immersion based on its actual geometry and
physical properties.
The project started in May 2006 with in situ data acquisition. The 3D geometry of the chamber was captured using a
Laser Range Finder. In order to combine the different scans into a complete 3D visual model, reconstruction software
based on the Iterative Closest Point (ICP) algorithm was developed using the Visualization Toolkit (VTK). This software
computes the boundaries of the room on a 3D uniform grid and populates its interior with "free-space nodes", through an
iterative algorithm operating like a torchlight illuminating a dark room. The envelope of the resulting set of "free-space
nodes" is used to generate a 3D iso-surface approximating the interior shape of the chamber. Each polygon of this
surface is then assigned the acoustic absorption coefficient of the corresponding boundary material.
A 3D audiovisual model operating in real-time was developed for a VR Environment comprising head-mounted display
(HMD) I-glasses SVGAPro, an orientation sensor (tracker) InterTrax 2 with 3 Degrees Of Freedom (3DOF) and stereo
headphones. The auralisation software is based on a geometric model. This constitutes a first approach, since geometric
acoustics have well-known limitations in rooms with irregular surfaces. The immediate advantage lies in their inherent
computational efficiency, which allows real-time operation. The program computes the early reflections forming the
initial part of the chamber's impulse response (IR), which carry the most significant cues for source localisation. These
early reflections are processed through Head Related Transfer Functions (HRTF) updated in real-time according to the
orientation of the user's head, so that sound waves appear to come from the correct location in space, in agreement with
the visual scene. The late-reverberation tail of the IR is generated by an algorithm designed to match the reverberation
time of the chamber, calculated from the actual acoustic absorption coefficients of its surfaces. The sound output to the
headphones is obtained by convolving the IR with anechoic recordings of the virtual audio source.
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