Underwater cameras are typically placed behind glass windows to protect them from the water. Spherical glass, a dome port, is well suited for high water pressures at great depth, allows for a large field of view, and avoids refraction if a pinhole camera is positioned exactly at the sphere's center. Adjusting a real lens perfectly to the dome center is a challenging task, both in terms of how to actually guide the centering process (e.g. visual servoing) and how to measure the alignment quality, but also, how to mechanically perform the alignment. Consequently, such systems are prone to being decentered by some offset, leading to challenging refraction patterns at the sphere that invalidate the pinhole camera model. We show that the overall camera system becomes an axial camera, even for thick domes as used for deep sea exploration and provide a non-iterative way to compute the center of refraction without requiring knowledge of exact air, glass or water properties. We also analyze the refractive geometry at the sphere, looking at effects such as forward- vs. backward decentering, iso-refraction curves and obtain a 6th-degree polynomial equation for forward projection of 3D points in thin domes. We then propose a pure underwater calibration procedure to estimate the decentering from multiple images. This estimate can either be used during adjustment to guide the mechanical position of the lens, or can be considered in photogrammetric underwater applications.
翻译:水下摄像头通常被放置在玻璃窗后面,以保护他们免受水的影响。球形玻璃,一个圆顶端,非常适合高水压,深水层,允许大视野,如果针孔摄像头恰好位于球体中心,则避免折射。将真正的镜头完全调整到圆顶中心是一项艰巨的任务,这既包括如何实际指导中心进程(例如视觉透镜)以及如何测量调整质量,也包括如何机械地进行调整。因此,这些系统很容易被某种冲冲抵,导致在球体上形成具有挑战性的重新折射模式,使针孔摄像头模型失效。我们显示,整个相机系统变成了一个轴形照相机,即使是用于深海勘探的厚角摄像头也是如此,并且提供了一种非直观的方法,在不要求了解确切空气、玻璃或水特性的情况下,可以比较球体上的反射线层地平地测量。我们还可以分析地平面上的反射线层测量结果,例如前对前向方向、后正正正正正正正的定位位置、正反射线曲线或前方平面平面平面的图,在使用这种平面的平面图的平面方向上,可以提出一种平面的平面图。