Forums >Technical Support>Which downloaded distance is correct, miles shown in data or on map?
When I download data from my Garmin 910xt to running ahead, the distance on the map page is almost always longer than the distance on the data page (which agrees with my garmin). Not surprising, the distance difference is greater the longer I run. Which distance is correct?
Thank you.
Uncertainty is woven into the fabric of the universe or something. Odds are none of them is definitively correct. How much difference are we talking about? I sometimes notice a tiny discrepancy, like a hundredth or two of a mile. I generally figure that's distance I traveled while the watch was stopped like if you stop to pee or if you stop your watch at a traffic light but don't hit the start until halfway into the intersection or whatever. It seems likely the distance on the map page is simply calculated differently than the distance on the data page.
Runners run
Your GPS device records a series of locations for you as you run. These locations are typically accurate within about 10 meters. These positions may be recorded anywhere from every second to every five seconds. Each GPS manufacturer and nearly every running log website that tracks GPS information has an algorithm to convert these positions into distance actually run. Since the algorithms are different, especially with how they deal with error, you are going to see variations in your total distance.
The distance on the data page is the one downloaded from your watch and is calculated from the GPS manufacturer's algorithm. The distance on the map page is the one calculated using Eric's algorithm for RA.
Hi Susan,
The difference between Garmin and RA's distances should be about 2%. Most of the GPSes if not all use a simpler formula to calculate distance between two points on a sphere. The earth is not a sphere. RA's formula accounts for that and tend to provide a slightly different number. One can argue that either is accurate.
eric
Labrat
Neither is definitively correct...
Both should be fairly close though.
5K 20:23 (Vdot 48.7) 9/9/17
10K 44:06 (Vdot 46.3) 3/11/17
HM 1:33:48 (Vdot 48.6) 11/11/17
FM 4:13:43 (Vdot 35.4) 3/4/18