Ask HN: Think GPS like system but local

Hey, actually i need to measure distance several points which will have barriers between them like human body and cloths etc...

I was thinking about infrared sensor but they can't pass through the body.

GPS does work to find distance between two points.

But can i setup a local gps in a room so it gives me accuracy in millimetres instead of meters like with ordinary GPS? If so, how? Can you suggest anything better?

Distance between two points is limited to 8 feet max.