Patent ID: 7450250

Claim:
A system for generating information relating to displacement of a surface of an object of interest, the system comprising: at least one retroreflector located on a surface of the object of interest; a first light source for producing light of a first wavelength, the first light source positioned at a first position on an axis; a second light source for producing light of a second wavelength, the second light source positioned at a second position on the axis; an imaging device positioned at a generally fixed, line-of-sight position relative to the object, the imaging device positioned substantially on the axis at a third position, wherein a distance between the third position and the first position is less than a distance between the third position and the second position, the imaging device receiving light of the first and second wavelengths reflected by said at least one retroreflector and by the object and converting the received light into a first set of electrical signals corresponding to the reflected light of the first wavelength and a second set of electrical signals corresponding to the reflected light of the second wavelength; and an image processing device, the image processing device receiving the first and second sets of electrical signals generated by the imaging device, the image processing device producing image difference information representing a difference between at least one image represented by the first set of electrical signals and at least one corresponding image represented by the second set of electrical signals, the image processing device processing the image difference information to determine changes in the position of the retroreflector, the image processing device interpreting the changes in position of said at least one retroreflector into information relating to displacement of the surface on which said at least one retroreflector is located.