The TV-trackmeter: an underwater noncontact position sensor

The TV-trackmeter is an underwater position sensor. Two TV cameras with parallel optical axes and known inter-axis distance are used to get two images of the same scene; a point in the space is projected into two separate points, one in each of the images. Through triangulation it is possible to identify the position of the image point in space. A powerful digital processor automatically performs the matching between left and right images, providing, within less than 80 ms, the 3D coordinates of the measured point; the accuracy is about 5 mm in the distance range of 2 m. The system can accomplish the tracking of the selected point in order to provide measurements always relative to the same reference point, even if that point is moving relative to the TV cameras. This tracking function is carried out by the digital video processor through an efficient code to reach a tracking measurement repetition rate of the order of 12 Hz. The measurements may also be carried out offline, on recorded TV images