{HEAD ~ 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 {TAIL ~ signals} based on the detected light rays for each of the light sources 
includes generating
{ HEAD ~ 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 { TAIL ~ signals } based on the detected light rays for each of the light sources
HEAD HEAD HEAD HEAD HEAD HEAD OTH REL 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 REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH