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Title
New perspectives to save cultural heritage
Author
Altan, M. Orhan

CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
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definition of the terrain-like pillar faces were simultaneously
defined. This implied that, in addition to the need of digitising
features for construct conventional plans of elevation, it was
needed the digitisation of random points on the faces of the
ashlars to record the roughness of their surface. We also traced
line-strings along sharp edges or around the hollows made by
the quarrymen's for the rock grab and following the deep
heading joints between the stone courses as well.
Once these “topographic” features have been digitised and
properly coded for their classification, the computer programme
needs to be set up so that it will be able to distinguish which of
these groups of layers gather random elements and which others
contain breaklines. That’s how, once each side of the complete
drawing has been folded down, a triangle mesh can be
interpolated in very few seconds.
Fig. 3. Triangle mesh model of a pillar face.
5. APPLICATONS OF THESE MODELS.
5.1 Obtaining sections.
Probably one of the most common problem derived from the
lack of a surface-topology in the graphic documents obtained
by photogrammetric restitution is the difficulty to section these
objects. This is specially an obstacle when they present blunt
and bulky shapes and their representation with lines is a
simplification biased by the point of view of the stereo-plotter
operator or draftsman (in fact, in most cases, if the 3D-drawing
are shown rotated, the lines no longer make sense and it is
difficult to recognize the figures). For example, a bas-relief
composed of human figures would be digitized as a few
silhouettes and some more linear work defining some features
and folds. If we wanted to obtain a section we would have first
to decide the position of the cutting plane while doing the
Figure 5. The digital surface model of an ideal reconstruction
of the ashlars can be faced to the current estate.
restitution and we would have to go along the section line with
the floating mark / pointer, which would often mean a great
deal of difficulty.
But once the TIN (triangular irregular network) has been
created by means of the drawn elements as a mathematical
representation of the surface, it can easily be sectioned along
any direction.
Fig. 4. For each pillar face we obtained horizontal sections at
one meter interval and three vertical.
The triangles cover the whole surface so that one can know the
third coordinate “elevation” of any desired point so that it is
possible to solve intersections between regular surfaces and the
network.
We consider that the constructed surface represent a good
approach to the true shape of the stone structure better than the
line-strings plotted during restitution. The interpolated lattice
makes objective the way-of-doing of the operator and makes
uniform the merge of sessions done by different people.
5.2 Volume calculations
Volume calculations enclosed by regular figures is a geometric
problem which involves a reasonable degree of difficulty.
However, the problem when trying to measure volumes of
shapes in sculpture figures, or any other irregular shapes (also
weathered pieces that have lost their original regularity)
becomes almost unsolvable. This difficulty is often work
rounded by the simplification or generalisation of the form and
assuming the error coming from the method itself.
From the triangular mesh models and through some
mathematical processes we can derivate other models of
regular square grids, which are very adequate for volume
measurement.
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