To evaluate the extrinsic parameters, you need the 3D coordinates of chessboard. Usually, without any other transformations, the 3D points used are (0,0,0) for the first corner of the chessboard, and logical'' position for the others, ie: (1,0,0) if you use a logical basis, or (2.5,0,0) if you have corners of size 2.5cm for a metric basis, etc.