Planar control in multi-camera calibration for 3-D gait studies

Abstract

The complexity of camera calibration has been a dominant limitation to whole-body movement studies in 3-D, especially in regard to the requirements on a calibration distribution in object-space. This paper focuses on photogrammetric calibration of a given camera configuration in which the usual requirement of a 3-D calibration object with known control point coordinates (“absolute control”) is circumvented. A calibration plane containing a 2-D distribution of known control points is placed at various globally defined positions and attitudes throughout the observation field, thus constituting a 3-D partial control distribution with the object-space coordinate system defined by one of these positions and attitudes; the unknown parameters of the remaining planes are solved for simultaneously with those of the cameras. The efficacy of the procedure is evaluated in terms of the relative influences of calibration and observation errors on dynamic target position reconstruction. Assuming equal error levels of the raw image data in calibration and reconstruction, the influence of the former may be rendered negligibly small using three exposures of 10–20 control points each.