Circles, such as concentric circles, arbitrary coplanar or parallel circles, are often employed for camera calibration. An interesting observation in football or basketball scenes is that a circle called the center circle existing in the midfield. By taking into account the midfield line which passes through the center circle’ center, a novel camera calibration method using the images of the midfield is proposed in this paper. A point at infinity can be determined from the center circle and the midfield line using the pole-polar relationship. The image of a point at infinity is called a vanishing point. The image of a circle is called a circle image in this paper. From one circle image and one coplanar vanishing point, a cubic constraint on the IAC can be obtained. The degenerate cases are discussed, and some applications are given in this paper.
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