By default, the unified projection model is used since this model approximates a wide range of cameras from normal cameras to catadioptric cameras. Note that in our equidistant fish-eye model, we use 8 parameters: k2, k3, k4, k5, mu, mv, u0, v0. k1 is set to 1. Typically for a set of 4 cameras with 500 frames each, the extrinsic self-calibration takes 2 hours. In contrast, the extrinsic infrastructure-based calibration runs in near real-time, and is strongly recommended if you are calibrating multiple rigs in the same area.