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I have a ticket, but there’s no boat!

All Europe Logs Are Up!

January 10th, 2009 at 4:19 pm

I’ve finished! I’ve posted all my journal entries, GPS logs, and photos from Europe!

Go check them out

Written by jarrod.carlson

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Bed Time Stories

January 8th, 2009 at 12:30 am

First of all, shouts to my “peeps” (meine Leuts!) who faithfully read this crap. Especially Bess, who gets her name mentioned right back. But you’re seriously gonna struggle through this one. I don’t know where I got it.

Sometimes when I jump into bed, instead of falling asleep, my mind just starts rattling off all the crazy random stuff it’s been turning over all day. Or week. Tonight is one of those nights, and I figured I’d let it out, since it’s more of a pondering point than a thought. It’s a little musing in the arena of statistics (hey, I loved Discrete Mathematics in college!). Here’s the story.


I took my little GPS receiver with me to Europe, and as a result, I got some pretty nifty logs. All over the places I went, I’ve got an overlay for a Google map that shows me exactly where I was and when. I suppose to some, that’s kind of creepy, but moving on.

Because GPS was developed by the military for, um, military purposes, it’s actually quite an incredible system. Wikipedia has a lengthy article on the technical workings of GPS, but the key thing is this: most civilian GPS receivers in the last few years are accurate to a few meters - about 16ft. If you’re really geek, the Wikipedia article also explains in depth why civilian GPS measurements are inherently inaccurate.

The GPS receiver then generally knows exactly where it is at any given moment in time - you just have to ask it. So along with the receiver, I brought a logger. The logger’s job was to record where the GPS says it was at any given moment, and this is where we get to the statistics. Since it would be very technically challenging to record absolutely every positional data point the receiver can produce, we have to sample it, much like a digital audio recording is actually a sampling of an analog signal.

The Experiment

I setup my logger to poll the receiver at regular intervals. Depending on where we were going and what we were doing, I varied that poll rate from one second to five minutes. Obviously the more frequent polling times produce more accurate logs, but they also result in significantly more data. The flight from Atlanta to Zürich, for example, at a one-second poll rate would have produced over 34,200 data points! But since we were traveling in a relatively predictable manner, I scaled it back to just a few hundred data points.

Okay, I’m getting to the point, I promise.

Generally, this means that a GPS receiver can report its current location with an error of up to 16 feet. And that 16 feet could be in any direction, as if the receiver were in the center of a 32-foot diameter Bubble Boy hamster ball. But the reverse of that statement is also true: a receiver may report its location with an error as little as zero feet - it could be dead on the money. I observed this effect in practice by looking at my GPS logs superimposed on a map. Sometimes the log point was exactly where I remember standing, and sometimes it was a ways off.

I used my GPS sometimes to measure how far I had traveled that day as well, sometimes walking as much as six or seven miles in one day. But the idea that the GPS is often inaccurate by a meter or more got me to thinking. With all that information in mind, consider this:

The Question

While on an excursion, would the GPS location samples, over time, average out to a spot-on measurement of distance traveled? Would the accuracy of the GPS samples increase with more frequent samplings or less frequent samplings? Would the samplings average more accurately over time, grow infinitely more exaggerated, or would the error level off in time, reaching a point of diminishing inaccuracy? Finally, what impact would my route have on the GPS’s measurements? Would a straight line path (such as an overseas flight) produce more or less accurate averages than a route that randomly meanders through the streets of an open market?

My comments after the break, but please, leave yours!

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-- Weather When Posted --

Location: Atlanta, De Kalb-Peachtree Airport

Temperature: 42.8°F, Humidity: 57%

Written by jarrod.carlson

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Beat the Board

January 4th, 2009 at 10:44 pm

I’m going to try this new incentivizing way of getting myself into the gym. I’ve created a motivation “program” I’m going to call Beat the Board.

The concept is simple - you have a Goal Board, and you must meet or beat the board, every day, to earn points. You compete against others not on goals but on points. More points gets you ahead.

To pilot this, I’m starting with a simple Challenge Series - Starter’s Challenge. We’ll be competing for a free dinner, paid for by the losers.

So if you’re interested or you just want to try something fun, let me know, drop me a line, or leave a comment, and I’ll get you the information (which you can also read here).

Written by jarrod.carlson

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Sleeping In Is Good For You

January 3rd, 2009 at 12:23 pm

According to new study, sleeping in those extra hours does a lot more for you than you might think.

I’ll have to agree - I haven’t woken before 11:00 the last three days and I feel fantastic!


Written by jarrod.carlson

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Happy Yew Near, Ya’ll!

January 1st, 2009 at 12:27 pm

Happy Yew Near!

Drunk girl on MARTA

Insanely drunk girl on MARTA. MARTA's pressin' charges.


New Year’s Eve. That special time of year when inhibitions are supposed to disappear. And any alcohol tolerance is out the door, too. On New Year’s Eve you drink like it’s your first time. Right?

Well, that was our plan. The four of us, Matt, Zach, Jesse and I, jumped on the MARTA and headed bound for Decatur to the Brick Store Pub. And then this happened.

Poor drunk girl was tossed onto the train by her wonderful friends. She was so drunk (at 22:00) that she couldn’t stand up. She literally fell onto the train, then crawled into a seat. Her head was never above her waist for more than about 10 seconds. She took her shoes off and curled up to sleep. We felt bad for her, and considered getting her off the train and into a cab (MARTA is no place for a girl, alone, too drunk to stand). But at the next stop, two police officers tried to get her up. She was oblivious, and the officers had to carry her off the train. I felt bad, but it was, admittedly, entertaining.

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Written by jarrod.carlson

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