Detection of liquids in cups based on the refraction of light with a depth camera using triangulation

We propose a method to recognize cups on desks and to detect liquids in cups with a depth camera using triangulation. When we measure an opaque liquid in a cup with the depth camera, the liquid surface is measured. On the other hand, when we measure a transparent liquid, the raised bottom is measured due to the principle of light refraction and triangulation. We formulated it theoretically, and confirmed that the theory is consistent with the experimental results. Therefore, it is possible to detect the existence of liquids in cups using the measured height based on this theory. In our experiments, the proposed method have successfully detected various transparent or opaque liquids.