What is the difference between 2d and 3d Digital image correlation?

3D Image Correlation provides full 3D coordinates of the surface of the material in test, using two camera stereoscopic view, which provides true deformation and strain data. 2D image correlation, uses one camera, providing relative displacement and strain data. As long as strain is greater than 1% and a longer lens is used, 2D can work well. 3D is much safer and more accurate.