Two Views of One Run

I had a chance of recording the same run with both Polar and Garmin. As I was running a known GPX route, I was curious to know how accurate the recorded location is.

In general, the reported location aligns well with the planned route. There is some jitter but it does not affect readability. There are also couple of segments where I intentionally deviated from the course:

To better appreciate the error between recorded and planned routes, let’s measure the distance from the recorded location to the line formed by connecting points of the GPX route:

Polar struggles more with recording of the location. If we compare the distribution of errors side by side, we get a sense of the error ranges:

+-------+------------------------+-----------------------+
|       |         Polar          |        Garmin         |
+-------+------------------------+-----------------------+
| count | 4578.0                 |                1062.0 |
| mean  | 9.294730823566551      |     6.444312595702126 |
| std   | 10.092639329570122     |     9.792494274172242 |
| min   | 2.1892964470737293e-05 | 0.0029163415626744277 |
| 25%   | 2.806925275018794      |    1.4672283547839986 |
| 50%   | 7.027681369141459      |     3.645489378596894 |
| 75%   | 12.141421692269327     |     7.527373215303927 |
| max   | 80.10267250523295      |     77.05301441506664 |
+-------+------------------------+-----------------------+

Two things worth noticing:

• Median error is 7 meters for Polar and 3.6 meters for Garmin.
• Polar has a lot more points (since recordings are every second vs Garmin’s ‘smart recording’)

The end effect of Polar errors is that the total distance recorded is 112 meters longer than for Garmin.

Besides location each device records elevation. This is where there is room for improvement for both Garmin and Polar.

Flat sections have unexpected spikes in elevation. However, when I climb up, elevation data is close to what it should be based on data from Strava:

Polar is measuring elevation with the built in barometer which is calibrated with GPS. While Garmin relies entirely on GPS to determine elevation.

With my Polar watch released in the 2018 vs 2023 edition of Garmin, the increased accuracy of Garmin is expected. The 4 meter range does not tell you which side of the street you are running on but does it matter? :)

Elevation errors come as a surprise but are not really a problem as long as the errors are consistent across the different runs to give a sense of how elevation is trending.

Want to repro or see data for your own runs? Check my Github repo:

• This notebook gives error in the recorded location. It requires importing GPX routes into PostGIS and running PostGIS with Docker.
• The rest of the plots are generated directly from GPX after parsing the files with this script.