Patent Document ID: 7737947
Application ID: 10687431
Patent Status: 1

Claim One:
1. A method for determining a first distance along a movement path on a surface over which an optical tracking device is moved by a user, comprising: projecting, from a coherent light source, and along the movement path, a beam of coherent light as a first light beam incident on the surface; generating, on the surface and along the movement path, a plurality of light interference speckles resulting from the first light beam and a second light beam representing at least portions of the first light beam reflected from the surface interfering with one another, the speckles having at least a first average spatial dimension; sensing the plurality of speckles with a plurality of light sensors arranged in a sensor cluster as the optical tracking device is moved along the movement path, each of the light sensors having a second spatial dimension that is less than the first average spatial dimension of the speckles, each of the light sensors further being configured to generate a first signal when one of the plurality of speckles is disposed therebeneath and detected thereby and to generate a second signal when one of the plurality of speckles is not disposed therebeneath and not detected thereby, and determining, on the basis of the plurality of first and second signals, the first distance.