Study On Ship Three-dimensional Deformations Measurement With Optical Collimation And Videometrics

Due to the effects of external stress and external environment, the sailing ship's deformations can not be ignored. For these deformations, attitude angles between the peripheral equipments and the reference center change. And the peripheral equipments can be radar antenna, optical measurement system and so on. To counteract the effects of ship deformations, corresponding compensations, based on Misalignment Angle of the peripheral equipments and the datum of Center Attitude Heading Reference System, must be taken. However, the law of ship deformations is so complex that there is still not a mature and effective ship three-dimensional deformations measurement technology both at home and abroad. For these backgrounds and application requirements, this dissertation researches on ship three-dimensional deformations measurement with optical collimation and videometrics. In the self-collimation optical path which is designed specially for three-dimensional deformations measurement, a CCD camera is used to capture the cross-line image, and the features of the image are calculated by sub-pixel location technology. Then, the three-dimensional deformation angles can be obtained by comparing the differences between the images. The main contents of this dissertation are as follows:1. To meet the requirement of three-dimensional deformations measurement, the self-collimation optical path, which can only measure two-dimensional flexural deformations, is ameliorated. The principle of the measurement is introduced in detail. Key issues of the measurement are analyzed deeply, for example, object-image relationship, the measurement of deformation angles and the range of the measurement, the relationship between the angle measurement accuracy and the image location accuracy, the working distance of the measurement, and the measurement errors caused by the optical path. And the requirement of high image location accuracy is brought forward by the analyses above.2. To extract deformation angles with high accuracy, this dissertation proposed an extraction method based on digital image sub-pixel location technology. The extraction process is divided into two parts: coarse location and fine location. Key issues which may affect the extraction accuracy of torsion angle are analyzed, for example, the cross-line's geometry features and gray distribution features, and the nonlinear relationship between torsion angle and the result of equidistant sampling in two-dimensional space. The accuracies of different sub-pixel location techniques are compared. Simulation results show that: the length of the cross-line is the most important issue in the extraction of torsion angle; gray square gravity method and Gaussian fitting method both achieve higher accuracies than others; when the length of the cross-line is longer than 800 pixels, torsion angle extraction accuracies of the two above methods are better than 1^″.3. Repeatability, stability, the relationship between measurement distance and repeatability, and the accuracy of three-dimensional deformations measurement are key indicators in three-dimensional deformations measurement. The measurement system proposed in this dissertation is set up to test the above indicators. Experimental results show that: the measurement achieve good repeatability and stability; due to atmospheric disturbances, the accuracy decreases when measurement distance increases; when measurement distance is 2m, repeatability of flexural angle is better than 0.05^″, and the accuracy of flexural angle is better than 1^″; repeatability of torsion angle is better than 0.8^″, and the accuracy of torsion angle is better than 2^″.