3 
> computer images, if a fairly accurate rendering software is 
available. 
Then, the number of the required panoramic views is set up: it 
can range from a few, to get a plan of the environment, until a 
dense distribution of photographs, to build a more detailed 3D 
virtual model. 
A good planning is an important issue for realizing virtual 
visits, mainly due to following reasons: 1) improvement of the 
on the field data collection step, 2) time reduction to convert the 
data in digital format, 3) optimization of camera stations setup, 
accor-ding to the working environment. 
3. THE IMAGE CAPTURE 
The shootingt is the most important step of the realization of the 
virtual movie. In order to meet the previously exposed mathe 
matical constraints, the optical centre of the camera must be 
aligned with its rotation point. This can be carried out with a 
particular tripod, adjustable at different positions. High 
accuracy (in order of millimeter) for the optical centre position 
is required only for very close objetcs. In this case slight 
misalignement can lead to changes of visible portions of the 
same object on conse-cutive frames. Dealing with environments 
where objects far and close from camera don’t occur, the focus 
setup, so as the check for alignement, become less problematic. 
For instance, if we see the same background behind the edge of 
a book, positioned in front of the camera, looking and moving 
the camera, thus the camera is aligned. 
The final result of building virtual visit is affected by camera 
objective as well. Choosing a wide-lens (max. focal length of 
28mm.) allows esier movements in vertical direction in the final 
movie, on the other hand the fish-eye lens allows to map the 
infinity (180°) on the image plane, but its strong geometrical 
distortions have to be to corrected prior to compose the pano 
ramic views. 
The camera is mounted vertically to take advantage of the view 
camera angle. The number of photographs, needed to cover a 
360° angle (see fig. 3), must be taken in such a way that the 
overlapping zone between two adjacent photographs is about 
30%. This allows to the algorithm, that produces the panoramic 
view, to calculate the right correlation between two images and 
to determine its best overlapping area. 
Figure 3 
4. BUILDING OF THE PANORAMIC VIEW 
Starting from the images acquired with a scanner, in order to 
build a panoramic view the STITCH algorithm is employed. 
Given the relationships (7) and (9) relating consecutive images, 
it is possible to perform an image mapping on any surface, on 
which a 2D reference system is established. In our case we use 
a cylindrical surface: this can be considered as a plane once the 
lateral surface of the cylinder has been unrolled. 
To build the image texture on this surface each photograph is 
projected onto the cylinder, calculating the focal length and the 
camera viewangle used for each snapshot. The mapping algori 
thm needs an initial estimate of the camera viewangle, then it 
provides the optimal angle that gives the highest correlation 
between each images pair. Due the time consuming of the algo 
rithm, it is advisable to test only two sample images and then, 
on the basis of the results, to apply the algorithm to all the 
photo-graphs. Among the parameters improved in the test we 
remember the following: 
> Horizontal offset between images 
> Vertical offset between images 
> Final height of panoramic view 
> The best camera viewangle 
The algorithm produces a cylindrical map pasting one after the 
other all the photographs. Note in fig. 4 - 7 the different results 
between a manual image pasting and that performed by the 
algorithm. 
In fig. 8 and 9 some results of image processing regarding the 
"Ancient Courtyard" of the University of Padova are showed. 
5. TEST AND RESULTS 
This technology was used to build a virtual visit of the "Ancient 
Courtyard" and of the Anatomical Theatre of the University of 
Padova. To the aim several camera stations were set up, 
namely: five inside of the Ancient Courtyard, two on the 
staircases that lead to the Courtyard and eight inside of the 
Anatomical Theatre. 
Some camera stations are resulted open, i.e. only a portion of 
entire environment could be viewed fom these positions, there 
fore only the more meaningful photos were taken. For some 
others stations the corresponding images were not used , due 
the overexposure of the photographs 3 . 
Anyway the results obtained for the Ancient Courtyard are 
excellent; these allow an interactive navigation in the courtyard, 
that is displayed to the user just as it is. 
In the Anatomical Theatre the image capture was difficult, not 
only due to the equipment setup, but also because, being a 
narrow and tall place, a lens with a very short focal length 
would have been more useful. 
The result however is good, although a visitor could desire 
more movement capabilities in vertical direction along the 3D 
virtual model. 
3 As the panoramic view results by the composition of two 
separate images, to avoid to let recognize the overlapping area 
the same light conditions in adjacent photographs have to be 
preserved. For this reason the camera diaphragm can be modi 
fied very slight, making useless those photographs taken in 
back lighting condition.