A short handheld video is enough to calibrate fisheye cameras for skylight navigation

Shuo Wang and three co-authors have described a way to calibrate fisheye cameras that measure the polarisation of skylight, which robots can use to find direction, in a paper on arXiv. Lens effects and imperfect polarising filters distort these measurements across the field of view; the method models both together with eight parameters.

It needs only a short handheld sequence filmed outdoors under natural skylight, without special calibration equipment or a model of sky polarisation. On real outdoor footage, it kept the mean error in the angle of linear polarisation below 0.5 degrees at all incidence angles. First tests with a camera on a quadruped robot showed better alignment with the sun's position, which the authors say supports using it to estimate heading.