5. The method of claim 1 , further comprising: establishing an imaging field of view; and defining a said region in said field of view; wherein: detecting said actor input comprises receiving at least one image of said field of view, with said actor input therein and in said region.
5. The method of claim 1 , further comprising: establishing an imaging field of view; and defining a said region in said field of view; wherein: detecting said actor input comprises receiving at least one image of said field of view, with said actor input therein and in said region. 27. The method of claim 5 , further comprising: determining a position of said at least one structural geometric salient feature in said at least one image; obtaining a second image of said field of view; and searching for said at least one structural geometric salient feature in a second position in said second image, said second position corresponding to said position of said at least one structural geometric salient feature in said at least one image.