Retinal optic flow during natural locomotion
Fig 11
Divergence, curl, and spiral flow patterns.
Canonical examples of Divergence (expansion), Curl (rotation), and the combination of divergence and curl (which produces spiral patterns. In the case of flowfield showing pure expansion (A—positive divergence), flow velocity is proportional to position on the grid—e.g. a step in the positive X direction results in an increase in X velocity (and similar for the Y direction). In the case of pure rotation (B—Curl) flow velocity increases in the orthogonal direction of the step—so a step in the positive X direction yields an increase velocity in the positive Y direction (for clockwise rotation/positive curl) or the negative Y direction (for counter clockwise rotation/negative curl). Summing the velocities of the divergence and curl flow fields results in spiral motion (C).