calibration process, and re-constructed after the photo is 
taken during each operation. 
A customized stand for the slide projector has 
been designed and manufactured in the Engineering 
faculty shop of the University of New Brunswick. This 
stand, on which an off-shelf 35 mm slide projector can be 
mounted, is used to facilitate the enlargement for the 
slide (Figure 3). After the enlargement, the image 
projected from the slide projector just about fills in all 
usable area of the digitizing tablet. The reason for this 
enlargement is to increase the resolution of the digitized 
photo coordinates in the original photo scale (Faig, et al., 
1990). 
Another solution would be using color films, 
rather than the color reversal films (slides), as the 
photographic material. For color films, the enlarged 
paper-prints can be used for digitization. In this case, the 
slide projector is not needed. 
The operation flow of this photogrammetric 
system is illustrated in Figure 4. Crush analysis is 
performed with the program package Crash 3 (USDoT, 
1986). 
THE DIGITAL EXTENSION 
The objective of this digital extension is to add the 
capability for accessing images in digital form. With 
digital images, the photo coordinates can be obtained 
from the display screen of the micro-computer. The 
advantages of having this extension are: 
* the slide-projector and tablet digitizer are no 
longer required. This would eliminate special 
office requirements, such as stable platform, 
working space. 
various digital image processing and enhancement 
procedures can be applied. In case of the poor 
quality imagery, these functions may be useful for 
human visual interpretation. 
» semi-automated or automated procedures, such as 
image matching, point extraction, even feature 
extraction can be implemented. This would ease 
the operator's work. 
* an automated indexing system can be installed. 
Images can be transmitted via network conveniently 
and efficiently. This provides an option for 
different MDAI groups to exchange their data and 
facilitate mutual discussions in an efficient manner. 
After the digital image is obtained. The hardware 
of this extension only requires a stereo-camera, and an 
IBM-PC compatible personal computer. In order to have 
quality image display, a VGA or Super-VGA graphic 
card and compatible display monitor should be used. 
Concerning the pointing device, although the arrow keys 
or other pre-defined keys on the key-board can be used 
to move the cursor on the screen, a mouse provides 
better human interface. 
In the current situation, film based cameras are 
used. Therefore, after the photograph is taken and 
developed, a scanning process has to be performed to 
convert analogue photos into digital images. Two types 
of scanners exist. One type is specifically designed to 
scan 24mmx36mm color slides, the other is manufactured 
for general documentation scanning. During the 
development, an HP ScanJet desktop documentation 
scanner was used. More discussions on the scanning 
process are provided in the next section. 
In the future, while the quality video camera and 
the digitization board become more affordable, the 
scanning process can be eliminated. For the video 
camera, no fiducial marks are required. The operations 
in Figure 4 can then be simplified into the operations in 
Figure 5. Details about the feature point digitization part 
will be described in the section of the semi-automated 
scheme. 
  
Slide Projector 
Stand Co) 
  
  
  
  
  
  
Figure 3. The Slide-Projector Stand 
  
  
  
  
Micro-computer