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.