Given the disparity d and 2D point (x, y) , we can derive the 3D depth using the 4-by-4 reprojection matrix Q as follows:
The reprojection matrix Q is given by:
The parameter cx is the principal point x coordinate in the left image, cy is y coordinate, while cx‘ is the principal point x coordinate in the right image, f is the focal length in pixels, x T is the x of translation vector between the two cameras.
原文：http://www.cnblogs.com/grandyang/p/4423895.html