OPTIMAL MARKER PLACEMENT FOR CALCULATING THE INSTANTANEOUS CENTER OF ROTATION

A computer simulation with error propagation was performed to determin e the optimal placement of marker points for calculating the instantan eous center of rotation (CR(i)). The authors assume that planar rigid body motion occurs between two positions, each defined by marker point s. Noisy marker points were generated by perturbing their coordinates with random values from a normal population of errors. The effects of these errors on the range of errors in calculating CR(i) location were investigated. Parametric analysis determined that marker point placem ent had important effects on CR(i) error. Marker placement was optimal when the estimated CR(i) was located at the midpoint between the mark er points. While increasing the distance between marker points increas ed accuracy, there is a critical distance above which no additional in crease in accuracy was noted when using this placement. The farther th e marker midpoint was from the CR(i), the greater was the error. At th ese placements, increasing the distance between the marker points cont inually decreased CR(i) error. The methodologies presented here help t o improve the accuracy with which the location of the CR(?)i can be ca lculated. However, it is emphasized that the CR(i) remains sensitive t o noise and investigators should apply this kinematic parameter knowin gly.