The method also includes detecting at least a portion of the reflected light rays with a photodetector associated with the set of at least four light sources, and generating signals based on {TAIL ~ the detected light rays} for {HEAD ~ each} of the light sources 
The method also includes detecting at least a portion of the reflected light rays with a photodetector associated with the set of at least four light sources , and generating signals based on { TAIL ~ the detected light rays } for { HEAD ~ each } of the light sources
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH