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New perspectives to save cultural heritage
Altan, M. Orhan

CIPA 2003 XIX 1 ' 1 International Symposium, 30 September-04 October, 2003, Antalya, Turkey
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Secondary grids descend from main ones with the
purpose of taking coordinates to the interior of the
rooms where you can place Total Station no-prism
instruments for tacheometric surveys in order to define
coordinates of spots on the object, to find its position in
the reference system in which the main grid has been
built and to fix visible points on the frames, the so
called anchor points, in order to orient these to the
outside. Recently a new logical necessity has been
pointed out. Every survey must be framed in a single
reference system and it should have the possibility of
referring itself to the cartographic national reference
system (georeferenciation). Georeferenciation is an
essential step when surveys are part of or are framed in
a Geographic Information System (GIS). From the
analytic or digital orientation of the frames we pass to
the generation of the DSM of the surface. In complex
cases, especially with a very high number of frames,
the automatic definition of many points in order to
correlate different images can be achieved through
aerial triangulation in order to build the DSM on which
the raster 3D digital orthophotos can be spread.
In San Lorenzo it has not been possible to limit the
survey and representation methods to one single
technique. It is the typical situation where the most
modern techniques (laser scanner, digital
photogrammetry,...) must be mixed up with the ancient
ones (manual-direct survey). Only through the
integration of these operative procedures, a complete
and exhaustive representation of the monument can be
Figura 1
1.6 Used instruments, software, mistakes, direct
San Lorenzo survey has been brought out using three
mechanized theodolites of the last Leica production
(TCRM 1103, TCRA 1103, TCA 2003), whose precision
characteristics are well known (several ten thousandths
of grade for the angular directions and some
millimetres for the distances). Two of them were
supplied with no-prism laser diastimeter for
tacheometric survey of interiors, exteriors, and anchor
points. The third, the most sensitive on the market, was
used to establish the grid reference. The whole external
part and in the intrados of the cupola in the interior
have also been set out with the LMS-Z210 Riegl laser
scanner. In the inside the Callidus laser scanner has
also been used.The software used to process the clouds
of points are the following: 3D Riscan, 3D Extractor
(Software owners laser scanner), Spider, StudioTools
(Alias Wavefront). The uncertainties in specifying
tacheometric points are always compatible with the
representation in scale 1:50 (0,2mm graphic error),
that is the centimetre. Even the exteriors and the
interiors determined with the laser scanner are
consistent with this accuracy. The integration with
measures taken directly with wooden ruler, measuring
tape, disto, always georefernciated to the tacheometric
points in the editing stage, has been outstanding.
The photogram metrical frames in the interior and in the
exterior of the Basilica have been made with the new
Rollei db44 Metric digital photogrammetrical camera
with 16 millions of pixels on a frame of about
40mmx40mm (1 pixel=9 micron) for the reproduction
of parts of the Basilica with digital photoplans, where
possible, and digital orthophotos.
Figura 2
1.7 Plans and sections
To this day the horizontal section at 1,50m of height
from the step floor has been completed at the nominal
scale of 1:50. The plan has needed the use of the
above said instruments, in addition to the definition of
"eidotipi" (sketches for drawing plans) with the direct
integration through the use of measuring tapes,
wooden rulers and distos: everything processed with
Autocad Map 2000.
The part of the section that has been surveyed by now
has followed the same procedure excluding a larger use
of the laser scanner system, no-prism theodolites and a
reduction of the direct survey because of the
inaccessibility of many places. The survey of the
basement will also follow the same method.
Some digital photoplans and several orthophotos have
been made for the exterior part (fig. 2) starting from
images acquired with the Rollei db 44 metric. The
photoplans, have been oriented and analytically scaled
on at least six anchor points. The resolution of these
frames is precise enough to support the scale 1:50, but
also 1:20 without loosing definition. Surveying can be
considered the natural support to the georeferenciation
of all the different kinds of analysis started
(mensiochronology, chemical analysis,