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Subsections

Active stereo

 Active stereo emerges as an alternative approach to the traditional use of two cameras. The word ``active'' here signifies that energy is projected into the environment. In an active stereo vision system, one of the cameras is replaced with a projector or a laser unit, which projects onto the object of interest a sheet of light at a time (or multiple sheets of light simultaneously) (Fig. 10). The idea is that once the perspective projection matrix of the camera and the equations of the planes containing the sheets of light relative to a global coordinate frame are computed from calibration, the triangulation for computing the 3-D coordinates of object points simply involves finding the intersection of a ray (from the camera) and a plane (from the sheet of light of the projector or laser).


  
Figure 10: Example of an active stereo vision system.
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Calibration

In the calibration step, a calibration target with a number of known 3-D non-coplanar points relative to a global coordinate frame is set up in front of the camera and the projector. After adjusting the lighting and the focus of the camera and projector, the camera is first calibrated, the plane equation of each sheet of light projected by the projector is then computed.

Advantages and disadvantages

An active stereo vision system has the following advantages:

Its shortcomings are:


next up previous
Next: References Up: Computer Vision IT412 Previous: Reconstruction of 3-D coordinates
Robyn Owens
10/29/1997