Exploration Of Temperature Effect On Videogrammetric Technique For Structural Displacement Monitoring

Displacement is an important descriptor of structural performance and safety.There are still many difficulties in dynamic displacement monitoring of large structures.In recent two decades,camera measurement has become a popular measurement method for displacement measurement due to its advantages of non-contact,long distance and high precision.In recent years,the research on camera measurement has emerged in large numbers at home and abroad,and has become a hot research direction in the field of civil engineering.However,as the camera measurement system is inevitably affected by environmental factors in the monitoring process,it is a test to improve the measurement accuracy.In view of this,the influence of temperature change on the camera measurement system is carried out,and the mechanism of temperature error is studied and a feasible method of temperature error compensation is proposed.2D videogrammetric measurement tests under monotonic or cyclic temperature variation are first performed.Features of temperature-caused measurement error and the casual relationship between temperature variation and measurement error are then studied.The variation of the temperature of digital camera is identified as the main cause of measurement error.An excellent linear relationship between them is revealed.After that,camera parameters are extracted from the mapping between world coordinates and pixels coordinates of the calibration targets.The coordinates of principle point and focal lengths show variations well correlated with temperature variation.The measurement error is thought to be an outcome mainly attributed to the variation of the coordinates of principle point.An approach for eliminating temperature-caused measurement error is finally proposed.Correlation models between camera parameters and temperature are formulated.By establishing the mathematical model between temperature and camera parameters,the camera parameters under different temperature changes can be predicted by the established mathematical model.By simplifying the imaging model,a simpler error elimination method is proposed,which greatly reduces the computation.Finally,this paper carried out the monitoring experiment of the dynamic displacement of the simulated structure by camera measurement.The practical feasibility of the error elimination method proposed by the experiment is verified by the field simulation experiment.By comparing the error mean value before and after error compensation,it is verified that the error elimination method proposed in this paper has good practical engineering application value and ability.