Calibration of a Projector with a Planar Gird

The projector is being frequently used in broad range of the photogrammetric measurements with the development of non-contact measurement in the close-range photogrammetry, because a projector can project any pattern onto the measured object for controlling and calculating. Before using a projector, the interior parameters of it have to be calibrated first. Hence, the projector calibration is a necessary and important preceding step. The paper proposes a flexible technique to make the calibration of a projector with a planar grid. This technique only requires an ordinary projector, a digital camera and a planar grid. The planar grid provides the main control ground and the camera takes photos as the image data. The camera demands to be calibrated or its intrinsic parameters are known. The algorithm with 2D direct linear transformation (2D-DLT) and collinear equations is used to calibrate the projector. The operation method in detail and the algorithm are addressed systematically and entirely. First, the image coordinates of the projector are designed carefully and the space coordinates of the projector are computed by the image data and the intrinsic and extrinsic parameters of the digital camera. Then, the decomposition of initial values of the projector intrinsic and extrinsic parameters using the correspondence of 2D-DLT and collinear equation is deduced. Finally, the projector calibration parameters are worked out by the whole adjustment. The feasibility and the exactness of the calibration technique of a projector put forward in this paper are verified by the results of real experimentations and data.