Parallax calculator for sprint split times

Why the cone does not go beside the finish line

The camera sees along rays: anything lying on the same line between its lens and a point ends up on top of that point in the video. The cone, though, you cannot put inside the lane, so you put it to one side. And a cone placed to one side, at the same metre as the finish line, sits on a different ray: in the video it appears displaced, and the time you read is wrong. The fix is to shift the cone along the track until it is back on the right ray: by how much depends on where you put the camera, and that is what this tool works out.

How to use it

1. Measure three distances and enter them in the Setup panel: how far the camera is from the lane, at which metre of the run you place it (counting from the start — if it stands before the start, a negative number), and how far from the lane you can actually place the cones.
2. Enter your finish lines in metres, comma separated: these are the distances you want the time for.
3. Look at the track from above. The blue dots on the running line are the real finish lines, the orange cones are where they go on their own line, and the dashed lines start at the lens. Every cone sits on the line of sight of its own finish line: that is what makes it right.
4. Check the second panel. It is what the camera will frame: the grey cone is the mistake to avoid, the orange one is the cone in the right place, vertically above the finish line.
5. Place the cones at the metres in the column where to place the cone. Not at the metres of the finish line: those are a different thing.
6. Film and read. The split is the frame in which the athlete's torso passes over the cone. How tall the cone is does not matter.

As a formula: x_cono = x_cam + (traguardo − x_cam) · D_coni / D, with D the camera–lane distance and D_coni = D ∓ Δd the camera–cone-line distance. If Δd exceeds D the cones would fall on the camera or behind it: in that case move them closer to the lane.