@article {Otero2003,
	title = {3D motion estimation of bubbles of gas in fluid glass, using an optical flow gradient technique extended to a third dimension},
	journal = {Machine Vision and Applications},
	volume = {14},
	number = {3},
	year = {2003},
	month = {Jul},
	pages = {185{\textendash}191},
	abstract = {To solve the problem of estimating velocities of gas bubbles in melted glass, a method based on optical flow constraint (OFC) has been extended to the 3D case. A single camera, whose distance to the fluid is variable in time, is used to capture a sequence of frames at different depths. Since objects are not static, we cannot obtain two frames of different height values at the same time, and to our knowledge, this prevents the use of common 3D motion estimation techni ques. Since the information will be rather sparse, our estimation takes several measures around a given pixel and discards the erroneous ones, using a robust estimator. Along with the exposition of the practical application, the estimation proposed here is first contrasted in the 2D case to common benchmarks and then evaluated for a synthetic problem where velocities are known.},
	issn = {1432-1769},
	doi = {10.1007/s00138-002-0117-7},
	url = {https://doi.org/10.1007/s00138-002-0117-7},
	author = {Otero, J. and Otero, A. and S{\'a}nchez, L.}
}
