So following up on my previous post Fixing altitude data in Mountain Bike GPS tracking:

I’ve since got a Samsung Galaxy S2 and the altitude data on that is better. It’s still off, but no where near as much as the E72 was compared to the corrected elevation survey data from Sports Tracks. Although Strava apparently do correction also based on the same or similar survey data, but I’ve found this differs from the corrections in Sports Tracks. Sports Tracks seems correct for some areas I know are a particular height though (classic being the height of Leith Hill in Surrey, highest point in south east England, which I know is 932ft and I spot instantly something is wrong when I’m seeing heights in excess of 1000ft).

However, next problem is the S2 GPS chip has low speed filtering enabled to optimise it for car navigation called Static Navigation. This is to filter out inaccuracies to avoid navigation jumping to side roads. In fact it’s funny reading about this because this was exactly a problem I was getting with the old Nokia E72 when navigating in a car in the US. It kept jumping to parallel roads! (and as their roads are straight, this happens a lot).

Okay, I thought I’d go back to my old bluetooth GPS which perhaps has a better antenna. Turns out it has the same chip though that does Static Navigation by default, the SiRF III chip.

Anyway, problem with Static Navigation is Strava assumes the GPS is always tracking and if there are pauses in the plot points it just assumes you’re moving still and thinks you’ve gone crazy speeds to catch up to the next point. I’ve had many incorrect KOM from climbs that I’ve done slow (or even pushed up!) due using auto-pause on Sports Tracker or Endomondo in the past and imported to Strava. I don’t use auto-pause now, but I get the same from problems from the Static Navigation.

Anyway, for phone tracking with Strava, the Strava app is preferred it seems as it gets around various issues and doesn’t auto-pause, but I then suffer from horrible location spikes in the S2. Often sending me 100s of miles away when I’m standing still! Might be the Static Navigation again though. This can be turned off but the phone has to be rooted apparently. Bluetooth devices can apparently be tweaked through serial commands you send to them, but they reset with it enabled when you turn them off/on.

For now I’ve gone back to the E72 to track using Endomondo with auto-pause disabled. Elevation data is once again way off though and Strava itself doesn’t correct it quite right so I use Sports Tracks to do that and import to Strava. This is the most accurate I’ve got, but still things screw up Strava further if you’re in a wooded area and the plot points make big jumps due to lack of GPS lock I guess.

Actually I’m wondering if GPS tracking logs the actual time for each plot point, as surely if it did this should never happen, as a lack of logged points should not make it think you did the segment faster! Would seems odd to not log the actual time given that time is a critical component of GPS.

*So* – most accurate Strava option – probably a Garmin or similar. These are designed for low speed tracking for walking and cycling, have better antenna, and also have a barometer for the altitude (though a couple of Android phones now have a barometer apparently). Just a question of whether you are that obsessed with Strava to justify the cost. My Strava use is really just for fun, comparing with friends and seeing where I’ve gone, but thanks to the leaderboards on segments it’s highlighting so many inaccuracies with GPS tracking on different devices.

Generally the only trust I have with the leaderboards in Strava is knowing who the people are on there. If I know it’s likely they can achieve that time, then it’s probably right, but some are so dodgy, and not just mine.