Using solar shadow trajectories for camera calibration

In this paper we show that solar shadow trajectories can be used for a robust camera calibration. Expanding on the previous work on calibration from solar shadows, we relax the condition that the shadow casting object be visible in the image. This enables us to work with shadows of non-vertical objects as well. The important observation that we make in this work is that these shadow trajectories form an interesting geometry 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), which we decompose for estimating the camera parameters. We show 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.