Photo Finish Tutorial

This Tutorial explains how to set up and connect phones to build a fully automatic timing system with our app photo finish.

FAQ:

►What is Photo Finish?

Photo Finish transforms android smartphones into a precise, fully automatic timing system optimized for track and field. Future updates for other sports (i.e. motorsports) are planned and will be announced.

►What is the advantage of a Photo Finish Pro subscription?

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 a Photo Finish Pro subscription. 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 a Pro subscription. So you can connect as many devices as you like with just a single subscription!

►What are the technical prerequisites of Photo Finish?

►How accurate is Photo Finish?

The accuracy depends on the accuracy of the camera clock of the smartphones used. It can either be medium or optimal. If all connected devices have an optimal camera clock accuracy, the accuracy is very high. With accurate alignment, the expected error is 0.01s or less. This makes Photo Finish more precise than a professional 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. If the accuracy is only "medium", there will likely be an error in the measured times. In our tests it was less than 0.05 seconds, so Photo Finish was still much more accurate than hand timing. A paper in which we explain the technical details of Photo Finish and compare the accuracy with a photocell system in a study is in planning and will be linked here as soon as it is published.

►What does the accuracy display mean when connecting?

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.

►Why does Photo Finish need access to the location?

Photo Finish uses Wi-Fi Direct technology to connect to other nearby devices. To use this technology, the app needs access to the device location.

►How does the detection work and why are there two images for each measurement?

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. By tapping on the image you can switch between the two images and check the correct detection of the chest position.

►Do you have a proof for the accuracy of the timing?

We plan to conduct a study with a high-speed camera to measure the precision of Photo Finish and compare it to a commercial light barrier system. The results of the study will be linked here. Until then, everyone can convince themselves 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.

[JacobMeza-pro-footballer]

Is it possible to add an out of the blocks mode for single session? I think it would be a good feature: even with single session you could always use a speaker for events like the 100 and then could be even easier for events such as the 400, 800, 1600, etc. Please consider 🙏🏽

[sebart]

This is amazing. Thank you so much for making this!

[physicswithmr.n]

This is great! I might see if I can use it in my physics classroom!

[ecogardening]

Thx so much for such type of information. I am track and field Coach and this app is very much usefull for me. So once again thx bro.

[tonjesolheim]

Will it react to several close crossings?

[belagajdan]

Do you consider making it so tje gunshot is made from the phone thats also the finish line for those who dont have 2 phones? It could measure the time between the gunshot and the crossing of the finish line. I would pay for that.

[desodonohoe]

Having ready set go on a single phone would be perfect. The go would start the timer and then the phone would capture the finish. I would pay for that!

[pflasterstrips]

Is there a out of the box mode for use with a singel phone?

[paminamiwebde]

Jungs Hut ab! Endlich mal was gutes und finanziell stemmbar. Gruß aus Neuwied

[borantoprakdaghan]

Hey fellas ! We just tried your app. İt's nicely thought. But there is an issue : The camera can't identify when we across the finish line in the nights.

Should we clock it in the daylight, or we got a problem with our phone. My friend and i tried it both with our phones but it didn't work.

[demokratess]

Danke für Eure detailierten Antworten :-)

Noch drei Fragen bitte:

Ich würde gerne Geschwindigkeiten bei ca. 30km/h mit +/-0, 1 km/h Genauigkeit messen. Dazu müsste ich am Ziel 2 Smartphones kurz hintereinander aufstellen ? Bei einer Auflösung / Meßgenauigkeit von Euch angegeben mit +/-0, 01 sek. sind das ca. +/- 8, 3 cm Genauigkeit auf die Strecke gerechnet bei diesem Tempo ?


1.)
Wie weit müsste ich die beiden Smartphones mindestens auseinander stellen (Delta), damit einerseits eine möglichst punktgenaue Geschwindigkeitsmessung bei rauskommt und keine mittlere Durchschnittsgeschwindigkeit für dieses Delta / Intervall. Aber anderseits die Meßgenauigkeit von 8cm nicht zu groß Einfluss nimmt in die Geschwindigkeitberechnung aus den beiden Differenzeiten 1. und 2. Smartphone ?

Wenn ich die Handys z.b. 1, 00 Meter auseinander aufstelle, dann ergeben 8, 3 cm Meßgenauigkeit eben auch 8, 3% Ungenauigkeit bei der Geschwindigkeitsberechnung also bei 30 km/h +/- 2, 4 km/h. Denk ich da richtig in Eurem System ?



2.)
Bezieht sich Eure Meßgenauigkeit +/-0, 01 sek nur auf das rein technisch / elektronische exakte Zusammenspiel, oder ist darin auch schon includiert Erfahrungswerte zu z.b. den unterschiedlichen Körperformen oder Abstände (Linse-Objekt), die von Eurem System erkannt werden müssen.


Auf was würde das System im aktuellen Entwicklungsstand fokussieren / messen, wenn ich z.b. auf meinem Rennrad über die Messlinie fahre ? Müsste ich dann aufrecht sitzend mit vorgewölbter Brust durchradelen, damit das System bei allen Radlern den gleichen Fokus und nicht beim einen das Vorderrad und beim anderen den Lenker erwischt ?


3.)
Wie definiert Ihr Eure Meßgenauigkeit +/-0, 01 sek ? Ist das der sogenannte "mittlere Fehler" bedeutet 99, 7% aller Messungen liegen innerhalb dieser Bandbreite vom "wahren" Wert entfernt oder nur Standardabweichung / Varianz ? "mittlerer Fehler" ist 3x Standardabweichung

Ich bin leider Vermessungsingenieur .... :-)

[michael__e]

Great job you two!!!

I have just one minor question
Did you installed different time schemes for the command or is it (still) always the same?
I highly recommand different settings

[brunocapel]

Bonne application pour mesurer un temps sur une distance qui m'intéresse.
Mes questions :
- Maintenant si il y a plusieurs coureurs au départ, est-ce que l'application pourra gérer le temps de tous les coureurs passant la ligne d'arrivée ?
- l'application est-elle multi langages ?
- Peut-on y ajouter une enceinte bluetooth pour un départ en starting-blocks ?
Merci pour les réponses à mes questions. 🏃👍

[gamewavelondon]

Can you Ready set go with just one phone?

[DrakiniteOfficial]

Really cool! Did you both do the programming for the app together?

[FinaISpartan]

How are you doing the connection between the phones? Wifi p2p groups? Bluetooth? Standard Wifi? Cool idea. I hope you guys have success!

[linoberlin]

Nette Idee, aber bin viel zu faul zum Rennen 👀

[mfive-vevo]

Why cant u used one phone for the ready set go

[demokratess]

Eine solche App zu entwickeln ist wirklich genial, mein Kompliment aus Scheyern ! :-)

3 Fragen hätte ich noch dazu.

1.)
Werden in der Bezahlversion die Finish-Fotos auf dem Smartphone oder Server abgelegt, damit ich mir diese später nochmal in Ruhe anschauen / downloaden kann ?

2)
ggfs. mit einem Zeistempel im Foto versehen ?

3.)
Wenn ich das Smartphone quer ausrichte, um möglichst breit-formatige Finish-Fotos zu erstellen um besser sehen zu können von den Läufern davor und dahinter, dann erscheint der Zielstrich leider horizontal. Kann man den um 90 Grad auf senkrecht drehen ?


Vielen Dank vorab für Eure kurze Rückmeldung

Jörg

[hughd]

Can you time a sprint with only one phone.... If so how do you do that?