A simple shadow based method for camera calibration

Using only shadow trajectories of stationary objects in a scene, we demonstrate that a camera can be calibrated robustly. We require at least two vertical objects to be visible in the image casting shadows on the ground plane. Using properties of these cast shadows, the horizon line (or the line at infinity) of the ground plane is robustly estimated. This leads to pole-polar constraints on the image of the absolute conic (IAC). We show that we require fewer images than the existing methods and demonstrate that our method performs well in presence of large noise. We perform experiments with synthetic data and real data captured from live webcams, demonstrating encouraging results.