An Efficient Solution to Ray Tracing Problems in Multimedia Photogrammetry for Flat Refractive Interfaces

Understanding and considering refraction effects are important parts of the demanding task of multimedia photogrammetry, especially with planar interfaces, so-called ”flat ports”. Yet, it remains challenging to determine reliable calibration results that are both quickly acquired and physically interpretable. In this contribution, a novel object-based optimization algorithm, relying on ray tracing methods, is introduced. It enables calibrating physical parameters of all involved refractive properties with reduced computational effort, compared to other standard algorithms in ray tracing. We show that this solution produces equally accurate results as other ray tracing approaches while improving processing speed by a factor of approximately ten and providing a statistical metric in object space. Furthermore, we show in a laboratory investigation that explicit calibration of refractive properties is crucial even with orthogonally aligned bundle-invariant interfaces for highest accuracy, as accuracy in object space is decreased by about 10% with implicit calibration. With deviation from orthogonality by about ten degrees this decreases even further to almost no useful results and accuracy loss of more than 50% compared to explicit calibration results.