Fixing altitude data in Mountain Bike GPS tracking

One of the problems I’ve come across with GPS tracking on mobile phones is the accuracy of altitude is somewhat poor. Reading a bit into this, it turns out that GPS is just plain not very accurate for altitude. The accuracy will generally depend on the device being used and what (if any) correction is done in software. This is why planes use other equipment for altitude and should never use the GPS for it.

On my old Nokia E72 the software I’ve used is Sports Tracker and Endomondo. Both come up with some crazy altitude tracking. One thing is they’re offset a lot, sometimes a couple of hundred feet above or below the actual altitude you’re at. The other is some crazy spikes whilst riding so the track seems to show you making huge climbs and descents along relatively flat terrain. Uploading into Strava this becomes more apparent as Strava highlights the Elevation Gain meaning thousands of feet of climbing when the reality is more like a few hundred feet.

So, aside from app makers doing some altitude correction in their apps, which requires obtaining physical location elevation data (much of which can be obtained from Shuttle Radar Topography Mission data), what you can do is fix the data yourself.

So what you can do is this:-

  1. Download and install Sports Tracks
  2. Install the Elevation Correction plugin by pkan (this does SRTM corrections)
  3. Export your track to a GPX file
  4. Import the GPX into Sports Tracks
  5. Go to Edit and then Apply Elevation Correction
  6. Export the GPX from Sports Tracks
  7. Import the GPX into your favourite tracker app now with the fixed elevation data

Note, this is all dependent on you riding at ground level. Maybe this is why apps aren’t doing the corrections as you may be tracking something like flying a plane, plus you could be going over a bridge or under a tunnel. For mountain biking though, it’s generally going to be accurate. Maybe the freeride and dirt jumpers are getting some height though, but near enough for all but the most insane ones doing crazy massive jumps and drops.

Other note is some GPS devices have barometers in them to aid altitude fixes. This is starting to include some GPS mobile phones.

Back Breaking

Got these from the check-up last month.

Means little to me and just look like a spine. Blurred CT scan from before supposedly shows T6 & T7 fracture. Stable Anterior Wedge apparently. X-Ray after said to them that it looks good. Fair enough.

Whatever the case I’ve been back on the bike since end of May which was barely over a month since the crash. Took it easy for a bit though, but scaled up a bit now. Fairly normal stuff now though have some fears of stuff that’s relatively easy on some days and not others. Confidence boost needed but definitely have a greater focus on risk and what I’m capable of. Doesn’t mean I’ll stop, but just if I know I can’t do it without practice and skill, then I won’t do it.

The broken back The broken back (healed)

Swinley crash, 9th April 2011

Unending Trees
It’s been a couple of weeks, so time I posted about my little smash on the bike.

It’s difficult to say what exactly happened as the result of this was I ended up in Frimley Park ICU and mostly unconscious for nearly 2 days. I have no memory of the crash or the 1.5 mile walk I apparently did back to the car park, or the ambulance, the helpful guys at GoApe, etc.

Can thank bungalistic though for picking up the pieces and getting me to the ambulance. Thanks also I understand to the folk at GoApe.

From what I understand anyway, after we’d been playing around Babymaker, Labyrinth & Deerstalker area, having a good time, we’d been heading back and found some drops and rolls to do. Seems I’d decided to try them out also, even though I’m not too skilled on drops. Though I’d been playing on the jumps earlier that day with some success.

Next thing apparently I’d disappeared over a drop and was found unconscious, then came to and managed to get back to the car park in a very confused state. Ambulance was called for and off I went to the ICU.

A lesson learnt from all this isn’t what I did or didn’t do, as I have no memory of it, but that it’s well worth keeping decent contact details on yourself for these situations, along with any information that medics may need. I had my phone but it was locked so fairly useless. Main thing of use was my donor card with my parents details on.

Considering how often I go out myself without telling anyone where I’m going and not carrying a great deal of info, it makes me realise it’s worth carrying further info. I do many group rides but no one has contact details for me, or I for them, so similar problems could occur.

Anyway, after finally waking up and being moved to a regular ward, I’ve improved fast. A week after the incident and left hospital, just with a couple of fractured vertebrae that look to be healing fine, and stiff neck, but fine otherwise.

It was just supposed to be a simple day playing about at Swinley, not doing anything too adventurous for me. Somehow it went a bit wrong. Ah well.

MOD polite notice to mountain bikers

Seems fair enough really and decent of them to not kick us off the land. There are increasing issues of conflict going on though, with unofficial trailbuilding, and interference with operations. That and the potential for getting sued by riders who take a tumble on the land is making the MOD jittery perhaps.

Note that similar signs are up about dog walkers also.

MOD polite notice to mountain bikers