International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B5. Istanbul 2004
2.5 Texture synthesis
As already pointed out, many elements are damaged in the
sense that parts have broken off. But the surfaces are also
eroded. As a result, the original textures and colours have
disappeared. Even if 3D shapes arc retrieved and restored, the
texture to cover them with in order to restore the full, original
appearance cannot be obtained from their available imagery. We
have in this case wetted the least eroded parts for some
materials to mimic the effect of polishing, and have taken
images of undamaged surfaces of the same materials but not
found at the site for the remainder. Based on such images,
texture models were generated and used to produce arbitrary
amounts of similarly looking texture (Zalesny, 2001). A total of
17 different building materials were used in this building. Fig. 7
shows example images for some materials, as well as synthetic
texture patches based on these examples. The necessary
amounts of synthetic texture were then generated for each type,
and with the necessary patch shapes to cover the elements to
which they apply.
Rather than describing these 3D modeling and texture synthesis
techniques any further, we here describe the additional steps
needed to put the components together into the final model.
2.6 Assembling the components
With blueprints (figure 8, top and middle left) as guidance, we
put all components together within Maya.
Of course, some elements couldn't be scanned, because they are
still missing or have been destroyed. Moreover, even if the 3D
capture technology is easy to use. scanning every block from all
sides is still too expensive (pieces would have had to be moved
with a crane). Therefore, the lacking components have to be
modeled by hand using common modeling methods like: curve
drawing and extrusion (translational sweep), solid modeling and
booleans, cutting tools, bevel tools, deformation etc. Further
reading on these methods can be found in numerous books (e.g.
Mortenson, 1985), software manuals (e.g. Alias, 2004) and
papers (e.g. Sederberg, 1986). Fig. 8 shows in the middle on the
right the hand-modeled back wall and the basin of the
Nymphaeum. The image on the bottom shows the fully
assembled monument.
To simplify the manual modeling process, 3D scans can also be
used as a shape outline one can constantly refer to. The efficient
and cost-effective nature of the ‘shape-from-stills’ pipeline
allows for this luxury. In addition, such coarse scans are much
easier to make than technical drawings for every construction
layer. Fig. 9 shows at the top the aligned scans and in the
middle the reconstructed model. Having both models, difference
functions can be calculated automatically and visualised on the
models, for example fig. 9 on the bottom: the grey areas
highlight the parts that had to be extrapolated from other
archaeological data, mainly from other pieces of the
nymphaeum. Such representation gives an idea of local
uncertainty about the model.
travertine limestone with limestone limestone marble from “white” limestone
deposit chert nodules breccia 1 block with Dokimeion crystallized breccia 2
pink styloliths limestone
(type 10) (type 3) (type 8) (type 6) (type 8)
(type 1c) (type 5b)
Figure 7: Example images of building materials (top) and synthetic textures (bottom) based on
models extracted from these examples.