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Abstract

Optical navigation upon grainy surfaces whose orientation is inclined at about 45.degree. to the X and Y axes of the navigation mechanism is enhanced by: First, detect that a spatial filter in use is inappropriate for the orientation presently occurring, and; Second, employ a different and more appropriate spatial filter subsequent to such detection. Two spatial filters have been developed that are respectively effective about the 45.degree. and 135.degree. inclinations of the Standard filter. The shape of a correlation surface used in the navigation process is tested for the presence of a transverse ridge in the correlation surface. This generates control metrics whose filtered excursions are tracked by a control system that changes the spatial filter in use. The control system incorporates a time constant to prevent thrashing and excessive sensitivity to isolated random variations. The direction from which illumination arrives relative to the X and Y axes affects the range of angles (relative to, say, the Y axis) that a filter is effective, by changing the apparent size and proportions of the highlights and shadows that are the perceived features ultimately navigated upon. Stable operation of the control system can be enhanced by ensuring overlap of the filters' ranges, and can be promoted by dynamically altering the direction from which illumination reaches the navigation surface, so that it corresponds to, or varies in relation with, the filter in use.

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