In outdoor scenes, polarization of the sky provides a significant clue to understanding the environment. The polarized state of light conveys the information for obtaining the orientation of the sun. Robot navigation, sensor planning, and many other application areas benefit from using this navigation mechanism. Unlike previous investigations, we analyze sky polarization patterns when the fish-eye lens is not vertical, since a camera in a general position is effective in analyzing outdoor measurements. We have tilted the measurement system based on a fish-eye lens, a CCD camera, and a linear polarizer, in order to analyze transition of the 180-degree sky polarization patterns while tilting. We also compared our results measured under overcast skies with the corresponding celestial polarization patterns calculated using the single-scattering Rayleigh model. © 2009 Information Processing Society of Japan.