A simple stereo television system with application to the measurement of three-dimensional coordinates of fish in schools

Stereo television is achieved through a rapid switch circuit that alternately selects fields from a pair of matched television cameras. Images are recorded with conventional VCRs. After image positions are digitized, stereo coordinates are estimated relative to a calibration grid, which may be removed during an experiment. Necessary geometry, including calibration and iteration procedures, is detailed. The method is flexible and accurate enough to allow the use of zoom, pan, and tilt on both cameras when a calibration grid is retained in view. Examples of the system’s application are given for the measurement of three-dimensional coordinates of fish in schools, both for glass-fronted aquarium tanks and in the natural environment using underwater television in sea cages.