GPS, Running Watches, Phones, Accuracy and other stuff pt 5
So, I got myself a Garmin Forerunner 3 - a basic running watch from Garmin, good enough for what I need
I also spent a bit of time re-plotting the route using the high accuracy OS Mastermap.
MasterMap in my neck of the woods is captured at 1:2,500 - which means it is 99% confident to be within 2.4 meters of the real world - see https://www.ordnancesurvey.co.uk/business-government/tools-support/mastermap-topography-support - without going out with survey gear and stuff, it is as good as you can get in most of the UK. (Larger urban areas are captured at 1:1,250 but those be big scary places, like Exmouth)
Using the new route I re-analysed the Gear Fit data and 4 runs with the Garmin, and here are the results - you can sort by the various measures (getting this working on Blogger took WAY longer than it should have)
| device | error area | samples | device distance (Dd) | OS distance (OSd) | Dd as % of OSd |
|---|---|---|---|---|---|
| Garmin Fr35 | 13742.4 | 1967 | 5035 | 5048 | 99.74 |
| Garmin Fr35 | 19929.67 | 2021 | 5040 | 5048 | 99.83 |
| Garmin Fr35 | 20326.25 | 1967 | 5049 | 5048 | 100.02 |
| Gf2 | 22917.26 | 2024 | 5067 | 5048 | 100.37 |
| Garmin Fr35 | 25638.39 | 1980 | 5057 | 5048 | 100.18 |
| Gf2 | 27854.41 | 2027 | 4877 | 5048 | 96.61 |
| Gf2 | 76162.62 | 2017 | 5148 | 5048 | 101.97 |
Four out of the five lowest error area results are with the Garmin, however, the old Gear Fit does hold its own on a good day.
The other interesting (to my mind) number is the %age of the OS measured distance the device measured distance is. It is always within 0.25% - which in meter terms is less 12.5m over a 5km run.
Conclusion - well don't be disheartened if your running watch says 4.99km at the end of a parkrun, that is well within what it is designed to do. The only real way of getting the exact distance is with a measuring wheel along the route.
Future idea - a bike computer is basically a measuring wheel, if it is calibrated with the exact circumference of the wheel, it may be the most accurate way most of us can get to a measuring wheel, so may be even more accurate than a GPS device.
