This is the method by which VidSync usually calculates the 3-D coordinates of a measured point. It is used by default, and it should be used in general when you’re filming entirely underwater (with cameras in underwater housings) or entirely in the air.
It does not work when filming through an air-water interface somewhere out in front of the cameras, such as for studies working through an aquarium wall. The more basic method should be used in that case and will still give reasonably good results.