Thursday, February 9, 2012

What do the horizontal squigglies in the race flow chart mean?

This is not the first time on this blog that we point out how much we like the Trackleaders' race flow chart. But it has its own surprising details. For example, if you look very closely, you see little horizontal segments that make me scratch my head a bit. Here is one on Allen Moore's chart, just a few status updates out of the Central checkpoint:

Remember, horizontal lines should mean that the team did not move, as the y-axis is location (and horizontal means location doesn't change, so they stay in the same place). Coming from the left, we see Allen's long horizontal line that signifies the end of his stay in Central. Then he takes off - the first check-in is from still very close to the checkpoint, and then he seems to fall into his rhythm. Except that between the second and the third track point, the curve is flat. For how long? Well, we can eyeball this as about 0.2 h plus/minus - that's close enough to 10 min to make me believe the problem is exactly 1 check-in interval long.

Now looking at Allen's individual track, he didn't stop for about 10 minutes (the time between two check-ins). Here is the relevant segment (blue arrow):

There are a few interesting things we can see by looking at this section in detail. The first is that the segment doesn't actually correspond to the usual 10 min check-in interval. It already looks too long for that naively. The endpoint was at 10:29:58 pm (this is shown on the screen shot), and the start point at 10:09:05 pm (you have to believe me here or check it yourself). Which means that right in the spot where the race flow chart has a 1-interval long horizontal squiggle the actual track is missing a point! This is what makes me think that the way the software draws the race flow curve, a missing data point gets replaced with the same y-value at the next point, thereby creating an artificial flat section. Well, that's my current opinion, and I'm sticking to it for a while, but Melinda is corresponding with Matthew Lee from Trackleaders, and he seems to think this explanation is wrong -- I'd be curious for his take on it!

The other interesting thing is that looking at the windy trail (on the tightly meandering Birch Creek) after Central, the track length gets cut across pretty badly across the check-on intervals. It would be nice to look at a speed chart across this section of trail.


  1. Hi Chris,

    Scott Morris from Trackleaders here (lead programmer). Really fun to read your observations here and general excitement for the race and the tracking.

    Race flow is one of my favorite features too, one that really tells the story of a race (for geek types, anyway).

    Some of the erratic "squiggles" are due to the coarse nature of trackline we have for the quest course. Sometimes they are due to the course line just being a little bit wrong, but often it's a lack of resolution.

    However, if the plot shows a horizontal line and the resolution of the track in that area is fairly good (as it is in #264 above for Allen Moore) it most likely means the racer did stop. If you use the "previous point" there's actually a point #263 behind it, with a speed of 6.9mph from the previous point. That's what caused the horizontal line in this case.

    I must say I am still a little surprised by the amount of variability in the plots for some areas of the course, so I plan to take another pass at the code soon.

    Thanks again for the comments.

  2. Hey Chris,

    I liked your possible explanation. I have thought about these things a bit and I think the fact that the same little features show up at the same mileage with different teams must give us a clue as to the cause. I don't think is all those teams stopping in the exact same spot for the same time. I suspect it's the course (red line) that trackleaders have and the undersampling (10min) in some sections. Seems like this is what Scott is implying?

    Regards, Darren.