GPS Tracking Atheletes
Tuesday, May 9, 2006
By JANET CROMLEY
LOS ANGELES TIMES
Cyclists, runners, walkers, even swimmers and windsurfers have gone global.
Using small, global-positioning devices, outdoor athletes are mapping their routes, tracking their distance, speed and elevation — even creating their own virtual training partners, ones that beep instead of speaking when athletes are ahead of, or behind, their target goals.
“If you’re a gadget person,” says Bruce Mosier, an avid runner and hiker from Santa Monica, Calif., “GPS is one of those things you absolutely need.” … Full Article here:
A rather interesting piece here, much too long to include in my blog post. It’s easy to see that GPS can do a lot for athletes in training. One point in the article though really caught my eye, and that is the practice of using GPS to tracking mileage.
Whenever you want to track miles on the earth’s surface based on signals from GPS satellites in space you need to consider a couple things. GPS is magic, but all magic has its limitations.
First, the repetition rate that your GPS receiver can maintain. No matter what brand receiver you use or how accurate the receiver’s design, they all can only do one thing … solve an equation based on measurement of distances from a number of satellites at an instant in time to give a three dimensional fix of location. Typically, better units can calculate a position every second. A decent runner may be covering 22 feet every second (that’s 15 miles per hour). What happens to the output of mileage data if even one data point is missed? There are a number of techniques that the GPS engineers may have used to handle this problem, but the point of this message is to get the user interested in finding out how his or her own unit handles discontinuities. There could be significant errors if “gaps” aren’t handled right.
Secondly, in it’s most basic and simplistic form; GPS handles equations as if the earth were a sphere. This works very well for many applications. When tracking a truck from New York to California the difference in mileage recorded caused by the fact that the earth, in fact, is not a sphere at all, will be negligible. But if athletes want to use these tool to make a ‘science’ out of training and measure performance down to the gnat’s eyelash … better make sure you are measuring the lash on the eye of the proper gnat. Consumer grade GPS receivers are highly unlikely to have proper corrections for distortions in the earth’s shape. Again, these distortions are of trivial importance over long distances, but trying to measure times in a 100 yard dash without considering them is going to lead to errors.
Bottom line … make sure you know what you are measuring before you try to manage with the data.