CrispyCSW

Hi all, newbie to the forum & GPS in general. I'm wondering if it is possible to use a GPS as a timing device? ie Have a set start & end point, and use the GPS to determine how long you take to travel between them?

If so, how accurate would it be? I'm guessing the limiting factors would be how accurate the GPS is in detecting when you are "at" the start or finish points", and how often that information updates (is it in seconds, hundredths of a second etc)?

My aim with all of this it have a way of someone verifying a time without actually having someone with them to do the timing. If they could submit a GPS track that passes through the start & finish points, and I could get the time from that, it would be great.

HumVee

CrispyCSW, that is very doable. There is positional inaccuracy (30 - 40 ft at both your start and end points) to consider, so it wouldn't be very accurate for short sprints - but for longer distances it should work just fine. Also, the position update frequency for handhelds is usually 1/second, so you couldn't get 10th's or 100th's time slices for foot races.

Of course, honesty would be an issue - if they submit to you a track file, it'd be childs-play to edit the info and make it look like you were faster than you really were. If you handed out GPS units at the start of the race, and collected them at the end of the race, that would eliminate that (but there would be the cost of all the GPS units to consider).

CrispyCSW

Thanks for the response. Looks like I'll need to think up a different approach - the positional inaccuracy would be an issue as I'm looking to time mountain bikers over a fairly short distance / time frame (ie downhill runs). Also, didn't realise you could amend the GPS tracks! I was planning on getting people to submit them via a website, so I can see that being a huge issue!!

HumVee

I understand that there are professional race GPS systems that are utilized for all kinds of races, including Formula One racing. That can do time slices down to thousands of a second, and accuracy within inches - but they are radio transmitter systems that are set up around the course...and I'm sure the cost for something like that would be far more than you or I could imagine spending for a mountain bike race! Good luck with your quest, and I hope that someone else on the forum has some ideas for you....

HumVee

I just had a thought...for foot races, such as marathons, they are now giving each runner a bracelet or hoop to attach to their shoe. These items are disposable RFID tags that each have a unique serial number. Then, they have sensors with time-synchronized clocks at the start and finish line, and as the runner crosses the starting line (& again at the finish line) a time stamp is recorded for each RFID tag that passes the sensors. I believe that they are very accurate - down to tenths of seconds if not hundredths. You might be able to rent such systems (& buy the RFID tags, which cost well under a dollar a piece when purchased in volume). If you used the same sensor for the start and finish line, that should make it all the easier to keep accuracy with the time stamps. You might research this option as an alternative to having everyone have a GPS unit and e-mail you their tracks. Cost of the competition enrollment could be raised a buck or two to pay for the RFID tags and rental of the sensor equipment....