The problem of determining the intrinsic and extrinsic parameters of a mobile camera is addressed. An optimal solution which consists of the following steps is presented. First, the camera is calibrated in several working positions and, for each position, the corresponding transformation matrix is computed using a method developed by O.D. Faugeras and G. Toscani (1987). Next, optimal intrinsic parameters are searched for all positions. Finally, for each separate position, optimal extrinsic parameters are computed by minimizing a mean square error through a closed-form solution. Experimental results show that such a technique yields a very large reduction of calibration errors and a considerable gain relative to other existing on-site calibration techniques.>