Hi. I was wondering if anyone could help me with the following problem. I am doing a independent lab at the moment. I am using video footage to measure displacement of a ball. I have cameras set up on the x and y axis where a ball is in line with the centre of both cameras. I have 1cm grids on the wall behind the ball in both directions. I apply a spin and a wind across the ball and use the video footage to measure the maximum displacement of the ball. So it goes... →camera → Ball → cm grid. The ball is in line with the edge of the grid in the y direction. The grid not in line with the camera - I have been informed - suffers from a angle of fore-shortening when looking at this part when measuring displacement on the video footage. I was wondering if there is a theory for this angle of fore-shortening or the best way to calculate how this will affect my results. Thanks.