ERATO Proceedings Istanbul 2006.pdf - Odeon

decorative features of the scene building. Concerning the Velum two contradicting sources were
available, namely the restitution plans by Izenour and the ones by de Bernardi.
In order to proceed in our virtual restitution the hypothesis presented by Izenour was kept as
reference because his assumption, based upon a parallel with the Rome Coliseum Velum, uses and
explains all the ropes attach points still existing at the exterior of the theatre.
Figure 5: Detail of the Velum Sliding sections (left), Aspendos Velum plan by Izenour (center left) and by de Bernardi
(center right) 3D virtual restitution of the Aspendos Velum, virtual restitution of the Aspendos Velum (right)
The hypothesis of de Bernardi on the other hand implies the creation of additional attach points in
order to keep the symmetry of the Velum and allow a correct placing of the sliding sections of the
Velum (details depicted in figure 5).
3.4 Lighting the 3D model
To further enhance the visual impact of the real time simulation of the Aspendos site, the addition
of diffuse and hard shadows cast by the sun plays a central role. At an earlier stage of the virtual
restitution a full texture baking approach of a pre-computed radiosity solution has been used This
approach however implies the creation of one texture per object: the bigger is the object, the higher
the resolution of the generated texture has to be in order to avoid visual discontinuities, therefore the
risk to overload the video memory, either with excessively high resolution textures or by too many
generated textures, is addressed.
Figure 6: Aspendos theatre rendered using a virtual light probe as input for the global illumination computation (left and
center), texture baked 3D model of the theatre (right) used for the real-time simulation.
To overcome these restrictions the adoption of a light-map and diffuse-map real time multitexturing
approach has been adopted due to the fact that the diffuse textures can be tiled, and
therefore their resolution becomes independent from the size of the object upon which they are
mapped, secondly the light maps can be downsized to very low resolutions without
compromising the overall visual impact of the simulation, thus eliminating the video memory
overload issue. In order to visually restitute a more convincing virtual illumination of the scene,
the use of High Dynamic Range Image Based Lighting has also been investigated, to allow the
rendering of diffuse lighting and soft shadows, in conjunction with the previously extracted
lightmaps, by means of multi-texturing, in order to render at the same time the hard shadows
caused by direct lighting (i.e. the virtual sun). In the first tests undertaken, HDR IBL was first
used to create the lighting solution used to perform the texture baking of the virtual diffuse
lighting, while the extracted lightmaps were used on the self-illumination channel of the
corresponding baked materials to render hard shadows (figure 6).