1 - INTRODUCTION:
AIMS AND MAIN CHARACTERISTICS OF THE RESEARCH
The research is open to the actual disciplinar
contributions and so it is having a remarkable
acquisition and updating in the area of digital
treatment.
The methodological process and the main
assumptions are here by indicated in their
essential parts. Owing to the relative topicality
of the research and the new formulation, there is
a temporary coming apart between finality and its
realization, between the identification of the
process through well defined steps and the
technical realization through different levels.
The application described here with the
realization of photogrammetric takens of a dome of
the St.Marcus' Basilica in Venice, the classic
restitution with an informatic output, the
evaluation of a DTM of the surface of the central
dome.
The dome image, digitalized by scanner, has been
projected on the DTM described above. Some closer
takens, still not utilized, has been realized too,
for the need of obtaining a greater resolution
that could allow some important evaluations and
comparisons in the aim of the research.
The images (fig.l) are obtained through a scanner
and a telecamera and later memorized in the
archives, for a first cataloguing.
The hardware utilized is reported in the following
list.
HARDWARE
IMAGE ACQUISITION:
scanner A3, 400 dpi Howtech,
24 bit (16 millions of colours)
output: TGA, TIF
IMAGE PROCESSING:
PC 486/33 Mhz
with graphic card Vista, 24 bit
(16 millions of colours)
Workstation IBM Risk 6000/320
Workstation HP 9000/835
SOFTWARE
IMAGE PROCESSING:
Pbmplus (on HP 9000/935)
Rayshade (on Risk 6000)
XV (Risk 6000)
Photostyler (PC)
Autodesk 3D Studio
Personal modifications
on Software conversion
Images given in the TGA and TIF formats permit to
obtain an high resolution connected with the
technical characteristics reported in the last
part of this research.
2 - DIGITAL IMAGES AND THREE-DIMENSIONAL SURFACES
In the evaluation of the state of conservation
made in this project the extraordinary mosaical
richness patrimony of both the plane (floor) and
curves surfaces (domes) could not be negleted.
The graphic restitution of the mosaical floor, has
shown all its limits. This technique is
insufficient for the interpretation of the actual
state. of a surface that has a considerable
undulation.
For such a surface we have tried to build up an
exhaustive three-dimensional synthesis that has
permetted to understand the progress of the floor
(Brumana, Crippa, Vassena, 1990), but has
introduced a separation from the various aspects
of matter and formal of the mosaic.
The knowledge of the state of deterioration and
the need to connect it to the geometry and to the
structure of the support has defined a preamble to
go over this gap. A book or a collection of images
has not the potentiality to realize such a link,
even if they have a great documentative. To
connect it to the geometry of the support it is
not sufficient the condition of measurableness,
obtained also with the well-known ortoprojection.
It is necessary to deform the image on the
belonging surface, later projected and visible
from different points of view. But it is not
enough to make a metrical projection so as to
respect a biunique correspondence between the
image-point and the corresponding point on the
belonging surface.
All this because the level of interpretablness is
equally important to identify the condition of
deterioration of a mosaical and decorated surface.
In particular when this surface is degraded by
phenomena of patina, of pulverization and of
material incompleteness.
2.1 THE ANALYTICAL APPROACH
The projection of the images of an object on its
digital-geometrical shape, obtained by
photogrammetry, needs to harmonize and optimize
all the different phases of the operation. The
images are acquired using metric or semi-metric
cameras and are digitalized through a scanner. The
angular parameters of the orientation of the
camera and thus of the image” are defined through a
classic operation of absolute orientation. These
informations are indispensable to drive, later,
the operations of images projection.