Full text: New perspectives to save cultural heritage

CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
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Figure 1. Matching of topographic data (red points) and photogrammetric restitutions 
demolitions, opening of traces, etc. - which are recognizable 
because constituted of homogeneous materials or processing. 
For the most significant USM, material type, processing, mortar 
type and stratigraphic relation were defined. As every USM has 
a stratigraphic position that defines synchronic or diachronic 
relation with the other, it was possible to assign, at first, relative 
dating among the USM and then absolute dating (still to complete) 
comparing data of the building with historic documentation. It is 
possible to summarize five most important constructive phases and 
relative wall types; a complete report was draw up for everyone. 
Normally, the USM are drawn on 2D geometric survey or, if it is 
possible, on image rectification, or, even better, on orthoimage but 
the relations among them, in complex cases like this one, is difficult 
to represent. A 3D model can be a real evolution in this analysis to 
merge reconstruction of consecutive stratigraphic layers. 
3.1 Geometric survey and 3D modeling 
Survey operations were performed during consolidations works. 
Thanks to the present scaffolding, it was possible to plan acquiring 
data at different heights, focusing on transept-apse complex to 
obtain prospects, vertical and plane sections at 1:50 scale. The 
articulated geometry, derived from a mixture of architectonic 
elements, structural damage and superficial decay, has required 
the survey of many points, imposing the management of 
numerous detail drafts to choose the representative elements. This 
approach combines the data from different sources: topography, 
photogrammetry, laser scanner and image processing (either as 
image rectification or as surface mapping) this has been integrated 
to obtain, finally, a 3D model. Some considerations on the adopted 
procedures follow. 
Increasing automation of the acquiring and elaboration of data 
processing are essential to widen the use of the 3D model, but 
despite this, at present, to represent and to elaborate data, is still, 
unavoidably, a selective operation: what changes is the moment 
in which synthetic interpolation, to obtain structured data, is 
required. With every survey technique we obtain a synthetic 
model of reality, but different cognitive approaches are available 
derived from different measurement techniques: topography and 
photogrammetry data collection phase requires a preliminary 
interpretation process, while, laser scanner acquisition collects 
redundant data, and synthesis is postponed to a post-elaboration 
2.1 Topographic survey 
Topographic techniques need graphic restitution, in which the 
object has to be defined with line interpolating measured points. 
The operator has to be able to interpret, at the moment of survey, the 
object of study. We can also say that with few measured points we 
can obtain exhaustive form and geometric representation, because 
additional geometric information derives from the operator. 
About one thousand detail points has been collected with a reflector 
less total station Leica TCR703, after having traced a small net 
of arrangement; the adjustment has been performed by using the 
least squares method. At the same time, about 100 control points 
have been measured - natural points on the transept, 40 targets 
on the apse and 17 specific Cyrax targets on the entire scene - to 
orient photogrammetric stereoimages and to define a reference 
system for range images. 
3.1 Photogrammetric survey 
In this case, measured data and represented data are approximately 
the same, except editing processing. Human critical selection 
about what to represent - autocorrelation algorithms, automatic 
restitution, furnish interesting results in small scale survey but are 
less applicable at the specific requirements of cultural heritage - 
takes place simultaneously at the restitution phase, with additional, 
well known, advantages derived from the separation between 
orientation and restitution phases. 
The images have been acquired by means of both semimetric 
Rollei 6006 camera (f=40 mm), and digital Nikon D1 camera 
(f=24 mm). 
With semimetric camera, three stereocouples have been acquired

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