Research On Fast Field Calibration In Measurement Of High Speed Vehicle Dynamic Envelop Curve

To precisely obtain the dynamic envelop curve of high speed vehicle is an important guarantee for safe driving.During the process of measurement based on binocular stereo vision,the field calibration is a key factor for the measurement accuracy.However,there are strict time limit and space limit,which raised high standard requirements on the quickness of calibration operation and the portability of devices.There are deficits in traditional field calibration such as time costing and the heavy equipment.Aiming at this inconvenience,analyzing the on-site condition,considering the practice of the program,the article conducts the calibration scheme of on-site parameters based on fast reconstruction of three-dimensional(3D)control field.Firstly,the 3D control filed is designed,which is of high accuracy,high stiffness,high portability and is easy to assemble.The overall mechanical frame,the linking and positioning design and the light point module are analyzed in detail.Then,the pinhole imaging model which is ideal and linear and the actual imaging model which contains many distortion factors are introduced.According to the requirements of camera intrinsic parameters calibration and the establishment of 3D control field,the total linear constrained optimization algorithm is adopted;considering the mathematical model of binocular stereo vision,based on the common calibration points of the 3D control field,bundle adjustment algorithm is adopted in the calibration of dual camera position.The railway center coordinate system is introduced,which is quickly established through the 3D control field,and based on least-squares optimization method,the space transformation relationship between camera coordinate system and railway center coordinate system is figured out.Through optimization experiments,the conclusion that proper amount of calibration points,proper relative position between cameras and the 3D control field and proper spatial layout of common calibration points are effective means for the on-site parameters calibration is made.At last,through overall experiments,the calibration method introduced in the article is proved to be of high accuracy and of high repeatability,based on whose calibration results,the measurement accuracy can reach ±0.5mm.Meanwhile,the quickness of calibration operation and the portability of devices are improved considerably.