| Summary: | 碩士 === 國立臺灣大學 === 土木工程學研究所 === 107 === Due to ultra wide-angle characteristics, fisheye lenses are widely used in artistic photography, surveillance application, forest science, self-driving obstacle avoidance, etc. Some applications that need to collect panoramic geo-information are especially suitable for using this kind of cameras. However, the imaging distortion of the fisheye image is significant, so the validity of fisheye lens calibration would largely depend on the correctness of geometric modelling between the image points and the object points. Since the fisheye lens has its own specific type of imaging formation, using collinearity equation attached by additional lens distortion parameters cannot set up a sufficient model. To achieve the relevant requirements of the metric measurement, this study adopts the rigorous object-image corresponding model to include geometric projection model for fisheye lens calibration. The discrepancy between the ideal image point and the actual image point is treated as the effect of lens distortion and modeled by additional parameters. This study aims to tackle effective implementation, including observation acquisition and optimal projection determination. Therefore, the contribution of this study is to support 3-D positioning with high precision under geometric projection models and to analyze, both quantitatively and qualitatively, the strategies of fisheye lens calibration. It is revealed from the experimental results that the object-to-image correspondence of fisheye lens based on the proposed model offers satisfactory geometric calibration quality. Strategically, the self-adatpive bundle adjustment with self-calibration for fisheye lens can be realized under sub-pixel image measurement quality at the expense of only 20 well-distributed coded targets and acquiring two images at appropriate locations to achieve the sub-pixel level of object point positioning. Thus, it is verified that the proposed methods and procedures can effectively and accurately implement the fisheye lens calibration. At the same time, the calibration result is also sufficient to support the mission of object point determination up to sub-pixel level quality.
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