thumb|working principle of a corner reflector thumb|100px|comparison of the effect of corner (1) and spherical (2) retroreflectors on three light rays. reflective surfaces are drawn in dark blue. a corner reflector is a retroreflector consisting of three mutually perpendicular, intersecting flat surfaces, which reflects waves back directly towards the source, but shifted (translated). the three intersecting surfaces often have square shapes. radar corner reflectors made of metal are used to reflect radio waves from radar sets. optical corner reflectors, called corner cubes, made of three-sided glass prisms, are used in surveying and laser rangefinding. the corner reflector should not be confused with the corner reflector antenna, consisting of two flat metal surfaces at a right angle, with a dipole antenna in front of them. ==how it works== the incoming ray is reflected three times, once by each surface, which results in a reversal of direction. to see this, the three corresponding normal vectors of the corner's perpendicular sides can be considered to form a basis (a rectangular coordinate system) (x, y, z) in which to represent the direction of an arbitrary incoming ray, [a, b, c]. when the ray reflects from the first side, say x, the ray's x component, a, is reversed to âa while the y and z components are unchanged, resulting in a direction of [âa, b, c]. similarly, when reflected from side y and finally from side z, the b and c components are reversed. so the ray direction goes from [a, b, c] to [âa, b, c] to [âa, âb, c] to [âa, âb, âc] and it leaves the corner reflector with all three components of direction exactly reversed. the distance traveled, relative to a plane normal to the direction of the rays, is also equal for any ray entering the reflector, regardless of the location where it first reflects. in diagram 1 the green ray is shown as reflecting from only one surface. this is a special case where the inco
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