Tuesday, March 6, 2012

Let's do some arithmetic

We're starting to reach the point in the race when leaders are beginning to sort themselves out from people who are out of contention and patterns are starting to emerge.  Granted, it's still early in the race and there's so much that could happen, but still, it's not likely that someone who's 100 miles back at this point is going to move into the lead pack.

But fans like to split hairs about who's in front, cite numbers from the GPS trackers, etc., so I thought I might take a look at the numbers and see if I can't help fans understand them a little better.

To start with, the GPS tracker displays are not providing very useful information about who's where.  They've got some anchor points and when a team is closer to a given point than they are to any other anchor point, they're assigned that "trail mile."  So, you can look at the tracker and have it be perfectly obvious that a bunch of teams are spread out along 5 miles of trail, yet the tracker will show them all at the same trail mile (see this).

I think that if you eyeball the map and the map scale and the mushers on the trail you can get a pretty good idea of just how far apart they really are, but if you want to calculate it exactly (and I know there are those of you who do), you can figure it out from their GPS coordinates.  Finding the distance between two sets of lat/long coordinates is kind of a pain in the tail, but fortunately there are some online tools to help you out.  I really like - no, I really LOVE - GPS Visualizer.  They've got calculators, they've got visualization tools, they've got maps, maps, and more maps, and I think they're the go-to resource for trying to solve map-related problems.  So let's do that.

Right now Aliy Zirkle is a few miles out of McGrath (and I suppose this is where I should say, "Two Rivers *represents*!  Go, Aliy woot woot woot!"  Okay, got that out of my system).  John Baker appears to be a few miles behind her.  Both GPS readings seem to have been taken at the same time.  How apart are they really?  I need to take two things into account: the distance between them according to their GPS coordinates, and the time differential that's going to need to be made up when they 24.

So, the first thing I'm going to do is go to the Calculators page at GPS Visualizer, where I see this a whole bunch of blank text boxes.  What I'm trying to do is calculate the "great circle" distance (shortest distance on a sphere) between two points.  I'm just cutting and pasting Aliy's values as is into "Lat. 1, Lon. 1" and John's into "Lat. 2, Lon. 2"  I hit the button that says "Distance->", and viola, we've got 2.566 miles between them:

So here's some crude arithmetic: if you figure they're running about 8mph, 2.566 miles is roughly 19 minutes apart.  One more piece of information: start time differential.  Aliy left Willow at 14:24, and John left Willow at 14:18.  That's really close together, but the bottom line is that John "owes" 6 more minutes of rest time than Aliy does, which puts them at about 25 minutes apart in reality.

So, for those who are really into the numbers, this is a pretty simple, straightforward way to get a more precise handle on where teams are in relation to each other than you can get off the tracker data itself.

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