I have co-ordinates (x,y,z) for three markers placed on the leg, and I need to calculate the position of a 'fourth' marker which appears in the first frame of my recording and then disappears. Together the four markers make up a rectangle shape, and the markers are fixed (one marker is on the inside of the ankle, a second is on the outside of the ankle, the third is on the outside of the knee, and the one I need to find is on the inside of the knee). I wonder if there is a way to calculate the co-ordinates of the 'fourth' point based on the co-ordinates of the others. I think this should be relativley simple but I don't know where to start!
Thanks!