優化魚眼鏡頭率定

Optimization of Fisheye Lens Calibration

10.6574/JPRS.202006_25(2).0002

楊軒(Hsuan Yang)；趙鍵哲(Jen-Jer Jaw)

魚眼鏡頭 ； 透鏡畸變 ； 幾何投影 ； 自率光束法 ； 內部約制 ； Fisheye lens ； Lens distortion ； Geometric projection ； Bundle adjustment with self-calibration ； Inner constraint

航測及遙測學刊

25卷2期（2020 / 06 / 01）

71 - 86

繁體中文

本研究為後續高精度（前方交會誤差毫米等級，或小於地面取樣距離）空間定位應用需求，採用基於魚眼投影幾何所推導出的物像對應模式搭配附加參數吸納透鏡畸變差。本篇文章主要著眼於魚眼鏡頭率定觀測資料蒐集面工作之優化，經實驗證實，於率定場中布設20個分布良好的率定標點以及位置適中的兩攝影站，並採用自率光束法搭配次像元像點與毫米級控制點觀測量，即可達至次像元之後驗單位權標準差（0.24 pixels）與前方交會誤差毫米級（＜5.6 mm，反投影約0.5 pixels）之率定成果，顯示本研究方法及程序能有效及精準執行魚眼鏡頭率定，同時，物像對應品質亦足夠支援次像元等級的物空間定位應用。

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. 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 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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