What Can Projections of Ow Elds Tell Us about the Visual Motion

The dimensionality of visual motion analysis can be reduced by analyzing projections of ow vector elds. In contrast to motion vector elds, these projections exhibit simple geometric properties which are invariant to the scene structure and depend only on the camera motion. Using these properties, structure and motion can be either completely or partially decoupled. We estimate motion parameters from projections of ow elds by using robust techniques, implemented in a recursive observer model. The model is applicable to general camera motion and to large eld of view and requires no point correspondence. We demonstrate our projection method on the problem of detecting independently moving objects from a moving camera. Using the projection approach, the problem can be reduced to a one-dimensional optimization process which involves robust line-tting and outlier detection. Instantaneous detection measurements are integrated temporally using tracking and spatially applying grouping of coherently moving points.