How to measure distance/position accurately


I am wondering if there is a way to measure distance between two movable points (e.g., the first point is on the hand and the second point is on the back of the human body).

I was looking at different types of technologies. I found ultrasonic sensors but those need a reflective object and this does not work with my idea. I thought about separating the transmitter and the receiver but there is the human body (hip) between those points and it can not be face to face. I considered technology based on magnetic fields so it can be measured regardless of obstacles or motion but I did not find anything close to what I want. And for infrared it needs to detect some object.

Is there any technology that can help me achieve this type of requirement?

Best Answer

You haven't suggested that the sensor should not physically interact with the body being measured, so given that I'm going to suggest a spool of line (automatically retracting) and a rotary encoder. You might need two spools to allow trigonometry to calculate the actual distance to the hand.