Correction Of Temperature-caused Image Virtual Displacement In Structual Videogrammetric Measurements

Displacement is an important reference index in evaluating the safety performance of structures.It is still difficult to monitor the dynamic displacement of large structures.In the past twenty years,videogrammetric measurement has become a popular method for displacement measurement due to its advantages of non-contact,distance and full field.In recent years,a large number of researches on videogrammetric measurement have emerged at home and abroad,and it has become a hot research direction in the field of civil engineering.The videogrammetric measurement system is sensitive to the installation environment,and the change of external environmental factors will interfere with the accuracy of displacement measurement.In view of this,this paper explores the law of the influence of temperature change on the measurement accuracy of the videogrammetric,focuses on the study of the image virtual displacement correction method caused by temperature,and puts forward a feasible method to correct the image virtual displacement.Firstly,the hardware composition of the videogrammetric measurement system,the principle of the keyhole imaging model and the common videogrammetric calibration methods are briefly introduced,which provides a theoretical basis for the experiment and data analysis in this paper.Then,according to the changing characteristics of outdoor environment,indoor simulation of ambient temperature was carried out under three conditions of controlling temperature monotone rise,monotone fall and cyclic change with air conditioning to carry out indoor research experiments on the influence of temperature change on videogrammetric measurement accuracy,and the correlation between image virtual displacement and temperature was analyzed.It is found that the change of videogrammetric temperature is the direct cause of image virtual displacement.After,according to the virtual displacement is mainly composed of image(CCD)as surface movement,put forward a method of accurate reference sample temperature to correct image imaginary displacement,and the three different posture by calibrating videogrammetric CCD displacement,surface displacement parameters of temperature change and the like are analyzed,and the quantitative analysis of different parameters on image virtual displacement effect size,found that the temperature change to any videogrammetric pose cases like surface displacement function influence.By establishing the mathematical model of the displacement function of temperature and image surface,the virtual displacement of image can be predicted under different temperature changes.The measured displacement minus the predicted virtual displacement is the real displacement of the image.Finally,the dynamic displacement monitoring test of the simulated structure is carried out.By simulating the actual The virtual displacement of the image is compensated by the field experiment of the dynamic displacement of the structure under the environment,so as to verify the feasibility of the proposed virtual displacement correction method.Through the quantitative analysis of the error mean before and after virtual displacement correction,it is proved that the error elimination method proposed in this paper has good practical engineering application value and capability.