Suggestion for proximity sensor?

[cfgrs]

Hello!
So, pet project. Basically, I'd like to be able to monitor the distance between two moving points, with distances varying from 0-2m or so, with a resolution of at least 5cm or so. (The actual application is to measure the distance between a person's feet while moving, running, jumping etc.) The two points will not be in a particular line (3D movement of both), and since I can't guarantee that their orientation will be controller, the usual IR or ultrasonic sensors I've seen won't work. I am allowed to strap something to each ankle.
Any simple sensors that I might want to look into that you can suggest? All I need is constant updates on the distance, I don't care about direction.

Thank you all!

 

[darkwood]

A few methods here to choose from but i can't think of any budget systems:-
A multi-camera system that feeds the real-time image into a computer to work out angles speed etc then give necessary results, or a wired or wirefree clothing as used in the CGI industry to mimic the bodies motion.
Both require complex software systems as far as I am aware but you could also look into biomotion systems similar to mentioned above on how they work but are used by areas like medical (for ppl with walking problems) or by sporting designers and atheletes trying to improve on products and skill respectively.