1. Introduction
Fisheye cameras have been widely used in many computer vision tasks [31], [34], [9], [16], [2] because of their large field of view (FOV), however, the images taken by fisheye cameras always suffer from severe geometric distortion simultaneously. When processing the geometric toward vision systems equipped with fisheye lens, calibrating the intrinsic parameters is usually the first step we should do to rectify the distorted images.