Towards calibration-free geo-localization of stationary outdoor webcams
This study proposes two strategies for determining the approximate geographical location of outdoor webcams based on time-series comprising regularly sampled images. The strategies require an accurate account of universal time and the date to be known, then the intensity of the images are used to estimate the sunrise and sunset times. Given accurate sunrise and sunset times a celestial model can be used to extract the latitude and longitude of the webcam. Webcams vary in quality, dynamic pixel depth and sensitivity to light. Two strategies are therefore proposed for avoiding the need to perform calibration. The first technique involves normalizing and noise-damping the image intensity measurements. The second technique employs a self-normalizing brightness ratio. The brightness ratio is computed from the overall brightness of the upper part of the image in relation to the bottom part. During day the sky is much brighter than the ground, while at night the sky is much darker than the ground if the ground is lit up. Experiments demonstrate that the intensity normalization strategy is the most robust and it is capable of determining the geographical location of webcams with an accuracy of approximately 2 degrees.
Sandnes, Frode Eika