Abstract: An aspect of the invention relates to a calibration standard for a three-dimensional measurement system and various calibration methods and techniques. The calibration standard typically includes a calibration standard surface and a plurality of optical targets. The optical targets being are affixed to the calibration standard surface and define a three-dimensional distribution of optical reference points. The optical targets can be serve as active, passive calibration targets, or combinations of both. In one embodiment, the optical targets include an optical source and a diffusing target, and each of the optical sources are configured to illuminate the respective diffusing target. The optical targets can be removably affixed to the calibration standard surface.