Accurate monitoring of large aligned objects with videometric techniques

This paper describes a new videometric technique designed to monitor the de formations and misalignments of large vital components in the centre of a f uture particle detector. It relies on a geometrical principle called "recip rocal collimation" of two CCD cameras: the combination of the video devices in pair gives rise to a network of well located reference lines that surro und the object to be surveyed. Each observed point, which in practice is a bright point-like light-source, is accurately located with respect to this network of neighbouring axes. Adjustment calculations provide the three-dim ensional position of the object fitted with various light-sources. An exper imental test-bench, equipped with four cameras, has corroborated the precis ion predicted by previous simulations of the system. (C) 1999 Elsevier Scie nce B.V. All rights reserved.