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GPS log of my commute.

September 2, 2005

A colleague lent me a GPS to plot my journey home on Thursady, and like Terry I would like the bike version for future use as this short exposure has the geek in me wanting more. The graphs show last nights home journey. My trusty speedometer told me that the stats for the journey were:

Time 59:33

Distance 20.90 miles (33.6km)

Average speed 21.0mph (21.06mph According to a calculator.) 33.7km/h

Maximum speed 40.00mph (54.39km/h)


To get home at 21mph on a Thursday was very special to me, I’m normally just to tired to go that fast. The motivation of having something logging the journey that I was going to pass to someone else was the only thing that made it happen. I tend to believe the speedometers idea of the maximum speed as I dropped down that hill at 10km in. The massive amount of down hill on the way home explains why I can go so fast!


I’m not entirely convinced about the altitude plot, particularly at the end. Clearly I need to get a GPS so I can get a better set of samples.


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From → Cycling

3 Comments
  1. Alan Burlison permalink

    GPS altitude readings are typically 3-4 times less accurate than position readings, due to satellite geometry. Make sure the GPS is held flat and has a clear view of the sky. Even tree cover is enough to cause them to lose lock. Most GPS units will interpolate direction and velocity if they lose lock, the result being that if you view the track on a map it will carry straight on even if you have turned a corner, then jump back to where you really are when it regains lock. This can cause speed anomalies.

  2. Thanks Alan
    I suspected as much.
    I’m definitely getting one of the new bike GPS that are arriving at the end of this year as the handle bar mount will keep the flat and they have barametric altitude measurement.
    I just hope the Santa is reading this;-)

  3. Alan Burlison permalink

    Yeah, I’ve got a Garmin that has an altimiter in it – you can either calibrate it by hand each time you use it or let it auto-calibrate, but that can take some time (and isn’t as accurate). Best bet is to find the height of your house – see http://bleaklow.com/blog/archive/000156.html for some tips. The other thing is that a lot of the units have a power save mode where the GPS effectively turns off for a bit. If you want to be hyper-accurate you should disable power saving (then buy more batteries!). On some of them you can also change the frequency with which they collect track log points, you could push that up as well.

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