CIP A 2005 XXInternational Symposium, 26 September - 01 October, 2005, Torino, Italy 
1042 
A NEW SUPPORT FOR TEACHING AND RESEARCH IN PHOTOGRAMMETRY: 
THE STEREOSCOPIC CLASSROOM 
S. Dequal, A. Lingua 
Politecnico di Torino - Corso Duca degli Abruzzi, 24 - 10129 Torino - Italy 
DITAG - Land, Environment and Geo Engineering Department 
Email: sergio.dequal@polito.it; andrea.lingua@polito.it 
KEY WORDS: Photogrammetry, Education, Three-dimensional Visualization 
ABSTRACT 
Stereoscopic imaging requires a minimum of two pictures, which simulate the perception of two eyes. This effect can be 
accomplished by using photographic images (stereo photography) or lasers (holography). 
Recently, a stereoscopic classroom has been equipped in the DITAG (Land, Environment and Geo Engineering Department), 
Politecnico di Torino, to support research and teaching activities in photogrammetry. The system is composed of a silver screen and 2 
high brightness projectors that use polarizing filters. The users (up to 15-20 people) can observe 3D models using specific (very 
cheap) glasses with polarized lenses. 
In this paper, the authors describe the recent activities using the stereoscopic classroom performed during the photogrammetric 
lectures in the degree courses and some research applications. 
1. INTRODUCTION 
1.1 What is "Stereo" or "3D"? 
The word "stereo" originates from the Greek and means "solid". 
Originally the term was associated with stereoscopic pictures, 
which were either drawn or photographed. In order to avoid 
confusion with stereophonic sound, one often talks about 3D 
pictures and especially 3D films, where 3D, of course, stands 
for three-dimensional. 
A person lives in a three-dimensional, spatial, environment. 
Without a feeling of space, we cannot move within it. Our 
perception of space is created almost exclusively by our eyes. 
There are many ways to orient oneself in space, e.g., by 
perspective, gradation of colour, contrast or movement. 
The lenses of the eyes in a healthy person project two slightly 
different pictures onto the retinas, which are then transformed, 
by the brain, into a spatial representation. The actual 
stereoscopic spatial observation is a result of this perception 
through both eyes. 
A number of people, however, have eye-defects, that make 
stereoscopic viewing impossible. They safely orient themselves 
in their environment by employing one of the previously 
mentioned methods. Even a person with only one eye learns 
how to move around safely, using non stereoscopic cues. 
Spatial 
Object 
left eve r '9 ht 
(b) 
Figure 1 - Stereophotos and their impression on the brain 
A normal picture on paper or film is photographed with only 
one lens and cannot, therefore, convey a true spatial perception. 
It is only a flat picture. By taking two lenses and imitating the 
eyes, it is possible to create a space image (Figure la). When a 
stereo picture is created in such a manner as to be examined 
with or without instruments, a similar perception of space is 
formed in our mind (Figure lb). 
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Figure 2 - Stereo photo acquisitions 
Two necessary, somewhat different, single views can be 
generated by different methods. They can be produced in the 
same way as old stereo artists did, first drawing one then the 
other single view. The exposures can also be taken one after the 
other with a normal single lens camera (Figure 2a). It is evident 
that the subject must not move during this procedure, otherwise 
the two pictures would not be related to the same scene. A 
better approach is to imitate the head, and mount both lenses 
onto a single chassis. In this way a true stereo camera is 
obtained (Figure 2b). This is basically only the joining and 
synchronizing of two mono-cameras. It is also possible to take 
stereo pictures with two coupled cameras (Figure 2c). The two 
lenses can also be combined as interchangeable optics in a 
single camera (Figure 2d). 
It is also possible to take two exposures with only one lens by 
placing a beamsplitter attachment in front of the lens. The 
splitter is constructed with mirrors or prisms or a combination 
of both. This divides the optical path so that two separate 
pictures are formed on a single film frame (Figure 2e). 
1.2. A brief history 
The belief that the ancient Greeks already knew of stereoscopic 
interaction has been proved a figment of the imagination. The 
same is true of the story that Leonardo da Vinci drew stereo 
pictures. These incorrect assertions stem almost exclusively 
from the English physicist David Brewster, who frequently 
wrote on stereoscopic matters. 
The true discoverer of stereoscopy was, in fact, another English 
physicist, Sir Charles Wheatstone (Figure 3), who also designed 
the Wheatstone Bridge. On June 21, 1833, he lectured to the 
Royal Society in London on his discoveries concerning 
stereoscopic phenomena. This lecture was also printed and his