Photo Finish transforms android smartphones into a precise, fully automatic sports timing system
Measurements with a single smartphone can be performed for free with Photo Finish. If you want to connect several devices in Multi-Session mode to measure e.g. 30m flying sprints or sprints from the starting block, you need Photo Finish Pro. If you want to try it out, go ahead! The first 14 days are free! If you cancel within the trial period, there are no costs at all. Furthermore, in a Multi-Session, only the mobile phone that creates the session needs Photo Finish Pro. So you can connect as many devices as you like with just a single Photo Finish Pro licence!
For Single Session Mode, you just need your Android Smartphone. In Multi-Session Mode, all connected phones need an internet connection for the transmission of times. Since wifi is mostly not available at the track, you likely need mobile data. If you only have one SIM card, you can also create a mobile hotspot with one of your phones and join with the other phones. Note that this is not recommended because of the limited range of wifi. Photo Finish needs almost no data (way less than 1 Mb per training session), therefore a small volume flat rate or even prepaid is completely sufficient.
No, you can also switch Photo Finish to front camera mode in the settings and lean it against a water bottle, for example. But be careful when you want to stop the clock or look at the times, so that you do not accidentally trigger a timing when you look into the front camera! However, we recommend a tripod for the best accuracy, reliability and usability, since the precise alignment of the smartphone in particular is otherwise not possible.
Extremely accurate: With precise alignment of the phones, the expected error is 0.01 seconds or less. This makes Photo Finish more precise than an expensive light barrier system. This is because Photo Finish uses image recognition to determine the chest position of the athlete. A light barrier can also be erroneously triggered by the hand or knee.
The accuracy is also very high in this mode, however, it is slightly worse than in Flying Start mode. The reason is that due to the Android operating system, there is a significant delay between sending a sound to the speakers and the time the sound is actually being played. This is a well known issue with the Android operating system known as the "Android 10ms problem". This delay depends on the individual smartphone, android version and configuration and is typically between 40 to 200ms. Photo Finish estimates the delay by listening to the microphone simultaneously while the gunshot is played. The actual moment when the sound is heard and the clock is started is estimated to be half the roundtrip time from the app sending the sound, the sound being played and heard simulataneously by the microphone and the microphone signal being sent back to the app. Some devices have a slightly asymmetric sound roundtrip time which can not be accounted for. Therefore, the accuracy of Photo Finish in out-of-the-blocks mode is slightly lower. The expected error is less than 0.05 seconds. Since there is currently heavy development in lowering the system audio delay on android devices, future updates are planned to reduce this error even further.
We have put a lot of effort into making the connection setup as stable and comfortable as possible. Nevertheless, it can occasionally happen that a connection setup does not work. In this case you can try to switch bluetooth off and on, restart Photo Finish, or restart the affected devices. A bad internet connection can also affect the connection process. In addition, when connecting more than two phones, it is recommended to join one after the other with the clients. Phones trying to simultaneously connect to a host can sometimes disturb each other.
Optimal accuracy ensures correct synchronization of the smartphone clocks. If the accuracy is only high, it is possible that the clocks are not perfectly synchronized, resulting in a measurement error of at max 0.1 seconds. However, this is very unlikely. In most cases, the clocks are synchronized to less than 0.01 seconds even with high accuracy.
Photo Finish uses Bluetooth Low Energy to connect to other nearby devices. To use this technology, the app needs access to the device location.
This increases accuracy. The reason is the varying delay caused by the operating system between the moment when Photo Finish plays the starting gun signal and the moment when it can actually be heard. Photo Finish uses the microphone to register the gunshot and can, therefore, determine the time at which it was actually played more precisely.
The analysis and calculation of the crossing time take a little moment. However, this does not affect the accuracy itself, just as the manual photo finish evaluation at competitions does not affect its accuracy. The beep is only played after the finish images have been evaluated.
Photo Finish takes 30 frames per second when the detection is active. This enables it to run in real-time on most modern smartphones, even on less powerful ones. An athlete crossing the finish line is thus captured 30 times per second and the chest position is calculated at the respective times. The exact moment at which the chest crosses the finish line is calculated using a cross-multiplication from the chest positions and the frame times directly before and after the crossing. This method allows to greatly increase the time resolution. Photo Finish displays the frame directly after the finish line by default.
With good lighting conditions and precise phone alignment, Photo Finish gets a really high accuracy. You can convince yourself of the accuracy with a simple test: Place two smartphones connected in multi-session mode opposite to each other on the same target line and align them exactly vertically and to the respective other camera lens. Then run across the finish line a few times. If the alignment is precise, both smartphones capture the runner at the same time. Typically the times differ by only 0.01 seconds or less.
You can set up the devices as far apart from each other as you like! This is the case because the transmission of the times happens over the internet. Note that the phones have to be close to each other (within 5 meters) during the connection process.