Poor visibility brings the safety issues to the automobile running on highway in fog weather. The research of vehicle distance measurement system can help driver better estimate the distance between the car and the car in front and make opportune anti-collision action even in poor visibility. Firstly, the related intrinsic parameters are obtained through camera calibration based on checkerboard image; Secondly, the geometric information of road markings and the position relationship between the

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... car and the car in front are extracted from the images obtained by camera; Finally, the real distance is obtained by the transforms from image coordinate to camera coordinate and then to world coordinate with the camera intrinsic parameters. It is proved that the experimental result is similar to the real value and meets the requirement. Furthermore, the camera self-calibration method which can reduce the impact of human action and make the foundation for the further study on camera calibration, is proposed.