The pq-histogram as a navigation clue

We propose a visual clue for navigation, in which the local 3D information or (p, q) is summarised in a single structure, called the pq-histogram. The pq-histogram is obtained by discretising in logarithmic scale the local depth (p, q). Since this histogram gives a global view of the scene, it could be used as a fast clue for navigation. An arrangement of four pq-histograms, one for each image quadrant, can advise many orientations. The potential application of the pq-histogram is illustrated in two domains. Firstly, semi-automatic navigation of an endoscope inside the human colon. Secondly, mobile robot navigating in certain environments, such as corridors and mines. In both cases, the method was tested with real images with encouraging results.