{TAIL ~ 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 the detected light rays for {HEAD ~ each} of the light sources 
{ TAIL ~ 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 the detected light rays for { HEAD ~ each } of the light sources
TAIL TAIL TAIL TAIL TAIL TAIL 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 OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH