The following note exchange discusses a growing problem with runners who don't think a course is accurately measured, because their GPS indicates a total distance that different than the race distance.
My response:
There is going to have to be some learning on the part of GPS users, because unfortunately they are not all that accurate, especially if you get into trees or areas with tall building that block the satellites. The signals from the satellites are even blocked by ones own body, which is why some of the manufacturers, not Garmin, have a separate receiver that you wear on the upper arm. I have the Garmin Forerunner which is the model I assume this person is using. My distance at the end of the Royal Victoria Marathon was something over 43km, not accurate but not bad if you are just out for a training run. Today I ran the Richmond Flatlands 10km and got 10.2 and I know it is 10km; I measurered it.
The Garmin, in generally open conditions, is usually 98% accurate, which for a marathon means 42.2+/-0.8km. The accuracy can be much worse than 98% if one is running through heavy tree cover or in the urban jungle. The person who wrote this note is well within the 98% accuracy at 26.6 miles. She is also mixing up her accuracies as the 15m accuracy refers to the position accuracy, not the total distance.
Sylvan, I am going to post this on the Measurement News Forum as I am sure it is a problem we will have to deal with more and more as the popularity of the these GPS units grows.
Paul
-----Original Message-----
From: Sylvan Smyth [mailto:sylvan@islandnet.com]
Sent: Sunday, October 16, 2005 2:16 AM
To: 'Laurie'
Cc: pauladams@telus.net
Subject: GPS Measurement
Laurie, what do you think of this blast RVM took on the marathonguide.com comments page for RVM? I think she's nuts and just ran sloppy, off the tangents.
http://www.marathonguide.com/races/racedetails.cfm?MIDD=62051009
"Victoria is an amazing city and race. I had a blast visiting the city and running the marathon. Unfortunately, the course is over by .40 miles. I was wearing a Garmin GPS that is 98% accurate within 15 meters. A friend of mine was wearing the same kind of GPS but came in 14 min. ahead of me with the same distance. 26.65. I only saw one other person in the race wearing one.
My time at mile 26 was a 3:41:12, now why in the world would it take me another 5 min. to go .20 if the course was accurate. It wouldn't be such a big deal, but unfortunately I missed Boston by 40 sec. Had the course been accurate I would have been 2 min under my qualification, but as it stands
26.61 miles, 3:46:40 time, 8:31 pace. I've e-mail the Race and course director about this, doesn't sound like the care too much. I'm one person in thousands. I will continue on my quest for Boston."
-Sylvan.
Original Post