2) Collecting the light scattered by the object in syn 
chronism with the projection mirrors; 
3) Focusing the light onto a linear position-sensitive 
photo-detector. 
4. THE BIRIS CAMERA 
The BIRIS range camera was developed at NRC of 
Canada to work in difficult environments where relia 
bility and ease of maintenance are important. 
The main components are as follows: 
• a mask with two apertures; 
• a camera lens; 
• a standard CCD camera. 
In practical implementation, the double aperture mask 
replaces the iris of a standard camera lens (hence the 
name bi-iris). A laser line, produced by a solid state 
laser diode and a cylindrical lens, is projected on the 
object and a double image of the line is measured on 
the CCD camera. 
The separation between the two imaged lines is propor 
tional to the distance between the object and the came 
ra and provides direct information about the shape and 
dimension of the object. 
As depicted in Figure 5, the line separations b[ and b 2 
represent the ranges Z\ and Z 2 respectively. 
As the camera calibration requires points of precisely 
known positions in the object coordinate system, a set 
of well-defined targets mounted at various hights on 
three orthogonal sides, was employed (Fig. 6 and 7). 
The main requirements for this field of controls points 
is the dimensional stability and the high accuracy of 
measuring the target locations after they have been 
built. The number and the distribution of these targets 
must be designed to completely cover the expected 
viewing volume of all the sensors. The points must 
vary in height but at least 10% of the stand-off distance 
to the cameras. 
L 
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Laser system 
jp&gp* ' i CCOctwwa 
BIRIS imoge Equivalent range image 
Fig. 5 : The BIRIS camera 
The calibration procedure was performed by placing 
the platform, where the cameras were mounted, in an 
initial position from which all targets were visible. All 
the sensor are to be adjusted at this stage, since no fur 
ther adjustment are permitted once they are calibrated.