Photo Finish

Photo Finish is the most accurate, but also by far the most expensive, method of Head race timing. It is widely used for lane racing, but in this case it is used to identify the gap between two finishers, not for times. It is rarely used for Head races.

The System

This is an image-based timing system consisting of:

• photo finish cameras and computers at each timing point
• an evaluator to take crew times from the photo finish images
• a network to synchronise the time on the computers, and to upload time to a results computer
• software to process the results.

Photo finish camera

This system uses a photo finish camera like the FinishLynx, or similar, to record images of the line at start and finish. The image is a series of scans of the line, only a few pixels wide. Because the scan is only a few pixels wide it can be performed at very high speed, unlike a full video frame.

Photo finish is typically used to identify the order of finishers in a close finish. However in a Head race it is not the order that matters, and so the system has to be adapted to provide results.

For a Head race the camera is started manually as each competitor approaches the start or finish line, rather than at a single starting gun. The camera scans are recorded on computer using photo finish software. The time is taken from the image showing when it was recorded.

Timesource

The FinishLynx cameras have optional timing circuitry. The timebase is a TCXO (see Clocks) with an accuracy of ±1ppm. This is more than accurate enough for a Head race, but it is less than the precision of the images.

Without the optional timing circuitry the times will come from the computer clock. The computer clock is not an accurate time source. When all competitors start at the same time, and finish within a few seconds of each other (as in a track event), this accuracy does not matter. But over the duration of a Head race it does. For accuracy the computer clock needs to be corrected by an external time source (see NTP Time Correction). The correction must be small and frequent, to avoid jumps in time. This means that the computer must either be physically connected to an external clock, or connected over a network with predictable latency.

Process

An Evaluator reviews the images and finds the frame where the bow crosses the line. The Evaluator saves the frame with the computer time.

It is not always possible to see the boat number in the line scan image. Therefore a Spotter and Sequencer are required to note the identity of the boat. To provide a verification of the boat identity a separate video or web camera can be used. The camera can be stationed at a different angle if necessary, or on the opposite bank.

A separate team at Start and Finish operates a backup stopwatch.

Network

An IP-based network is used to transfer the image files to a results computer.

Results software

Results software like Regatta Master is designed to take an input from photo finish cameras. Penalties and handicaps can be added to the times to produce the final results.