A way to measure distance between people walking in a room from top-view cameras

I am looking for a way (software or etc.) that can track a live distance of the three to four people inside a room from a top-view camera recording and calculate each person (dot) distance from each other or some default references in the room.
This is going to be a social neuroscience research and I hope I can use the help of this great community to learn about how to handle this experiment.

Thank you very much!


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