Data glitches

While pondering data graphs from my cycle computer, I wondered why the axis always had very high values on them. For example, on the graph to the right is from Friday’s commute. The “speed” range is -25mph to +125mph. Even more puzzling, there is a point on the graph where I am apparently going 87 miles per hour on my bike, probably close to my terminal velocity.

It’s clearly a glitch.

The unit (Garmin 305) has an auto-pause feature that stops recording when I’ve stopped. It’s similar to what’s on most cycle computers, and is useful because you don’t necessarily want your workout data skewed by the unfortunate whims of the Factoria traffic lights, especially when the fire engines muck up the timing.

Sleuthing around, I’ve noticed this problem consistently occurs near a tunnel crossing under Interstate 90. When I enter the tunnel, the unit loses reception with the orbital mind control satellites, assumes I’ve stopped, and chirps. When I emerge from the tunnel, it chirps again to let me know it’s restarted recording. My theory is it calculates I’ve moved 500 feet in “no” time, interpreting this as dangerously high-speed tunnel surfing. The axis maxima is based on this spurious value, rounded to a “nice” value.

Two miles later, a second glitch occurs where the gradient approaches 60%, or four times the steepest hill I normally encounter. I’m guessing this corresponds to the elevator at work: I forgot to hit the “off” switch early enough.

The Garmin replaces:

  • Polar S710 heart rate monitor. I’ve had this for five years (to the day). The Polar’s an okay unit, but depends on an infrared port for data transfer. My laptop doesn’t have one. There’s a USB thingie available, but that’s $35. The batteries are also shot, which would add another $50 to get them (watch + sensor batteries) replaced.
  • Garmin eTrex Vista GPS. This is one of the older, moving map models. Its mechanism for data transfer is a serial port (you guessed it – none). Loading the 24Mb with maps often took over an hour, but it came in handy on a few occasions.

As I discussed with Scott, what we really need is to lump a cell phone and mp3 player into one unit — with reasonable battery life — and We’d Be Mostly Happy with the hardware. I’m not much of a repetitive laps person. I’d prefer the “Start/Stop” button was actually for starting and stopping, not laps. (There is a separate lap button. I think this may summon a pizza delivery.)

The other hardware change I’d like is having it scroll through numbers. There are separate screens where one can put up to eight data points each. Naturally I put in all eight. But there are other interesting metrics I’d like to see.

As far as the software goes, in addition to resolving the issues above, I needs a way to edit data points. Glitches will happen. Smoothing helps hide these, but it won’t remove them. Also, I’d like to see an easier way to label and compare trips taking reality like long traffic lights into account. For example, there was construction on West Lake Sammamish. If I could create checkpoints, it would let me negate unplanned sections like slogging through the traffic constipation. Finally, I’d like a Google Maps/Bikely interface.

3 thoughts on “Data glitches”

  1. Hmmm…I have the Garmin Edge 205 (since I’m still using my Polar S725 HRM – but data transmission to PC is becoming flakey at times).

  2. I have a Garmin GPSMap and I have been able to smooth out glitches by loading the data into the map software and deleting the outliers. It will just average out the speed over the missing interval. The GPS does strange things when the signal is lost, like walking on water. I always lose the track on West Lake Sammamish Parkway for some reason. It starts projecting the last course and speed then jumps to the next good fix.

  3. Sign up for MotionBased and you can view your course on Google Maps (as well as an export option to Google Earth). It also interprets the data a little differently than the Garmin Training Center software. I don’t know if it will cure your glitches but it seems to understand when the signal drops out you haven’t magically teleported between the last two known points. They’re owned by Garmin and have a free membership option that lets you view your last 10 rides.

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