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Abstract

A method of position encoding in convergent beam scanned imaging systems (10) is provided that reduces distortion. Distortion of a scanned image is introduced in convergent beam systems through the application of mirror 'pullback' at the limits of the scanning sector, which is required to retain focus over the field of view or scanning sector. The rotational position of a scanner mirror (14) is not proportional to the spatial scanned angle or object space angle (.delta.) due to this pullback, and thus introduces distortion. Various components of the pullback motion are utilized to provide the compensation required to overcome this distortion. A process is provided that determines the position of a mirror position detector such that the pullback translation motion of the scanner mirror (14) is used to compensate for the nonlinear rotational motion of the scanner mirror (14). This is accomplished by locating the mirror position detector (16) at a predetermined radial distance and angular position with respect to the scanner mirror (14) point of rotation and sensing the rotation of the scanner mirror (14) and pullback. By appropriately selecting the angular position of the mirror position detector (16) with respect to the scanner mirror (14) center of rotation and the direction of pullback, the output of the mirror position detector becomes a substantially linearized representation of the object space angle (.delta.). Significant reductions in distortion can thus be obtained via optimizing the angular position of the mirror position detector (16) through an iterative mathematical approach performed by a computer.

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