Correcting out-of-plane errors in two-dimensional imaging using nonimage-related information

Two-dimensional imaging with a single camera assumes that the motion occurs in a calibrated plane perpendicular to the camera axis. It is well known that kinematic errors result if the object fails to remain in this plane and that if both the distance to the calibration plane from the camera and the distance out-of-plane are known, an analytical correction for the out-of-plane error can be made. Less well appreciated is that out-of-plane distance can frequently be acquired from other, nonimage-related information. In the two examples given, the mediolateral center of pressure coordinate of the foot measured from a force plate and the measured landing point of a shot put throw were used. In both cases, the resulting out-of-plane correction improved the accuracy of the 2-D kinematic data dramatically. These examples also demonstrate that the use of nonimage-related data can increase the accuracy of kinematic data without an increase in the complexity of the experiment.