How accurately can direct motion vision determine depth?

The use of direct motion vision for determining the depth of a scene is investigated. To permit direct comparison of analytical and experimental results, only translational motion and planar patches of constant depth are considered. The analysis shows that the accuracy with which depth can be determined increases with the sum of the squares of the temporal derivatives over the patch; this quantity is referred to as the apparent size of the patch. After determining the relationship between relative depth error and apparent size analytically, a number of experiments with camera-generated image sequences were performed. In nearly all of these experiments, the agreement between the analytically determined and measured values of the relative depth error is very good