Homography from Conic Intersection: Camera Calibration based on Arbitrary Circular Patterns

For the camera calibration, point correspondence data between 3D and 2D points widely spreading over the image plane is necessary to get a precise result. However, in the case of wide observing area, it is impractical to use a huge calibration object that covers the camera view. This paper presents a refined calibration method using circular patterns. We already proposed a circular pattern based camera calibration method using a four-wheel mobile robot. That is, by keeping low speed and constant steering angle, the robot can draw a big circular pattern on a plane. Our previous method, however, has a limitation that roll angle around the optical axis is assumed to be zero. This paper presents an improved version of the camera calibration method. Our method estimates the extrinsic parameters of fixed camera from a single circular trajectory when the focal length of the camera is known. In the case that the focal length is not given, two co-planar un-concentric circular trajectories are enough for calibrating the extrinsic parameters and the focal length. In both cases, the center and the radius of the circle(s), the speed of the robot are not required. The extensive experiments over simulated images as well as real images demonstrate the robustness and the accuracy of our method.