GPS drawing redux: When electronics go awry

A few nights ago I worked with a group of 4-Hers to teach them about GPS units and create some "drawings." (The girls and I had done our field work earlier in the month to test out GPS drawing and experiment with designs to prepare for this.)

But the night of the class the thermometer outside displayed single digit temps. The kids did OK with this (well, except that a couple of the teens opted not to wear winter coats, which gave me a glimpse in to what the future may hold for me when my girls are a bit older).

The GPS unit however, did not care for this kind of cold.

Things started out OK with the first small group I took outside to draw. Their first drawing of a box (renamed "barn door" when presented to the rest of the group so it sounded more interesting) came out as expected.

And the "snake" was OK too even though the kids did not cover enough square feet for the head (the GPS unit's accuracy is only 8-10 feet so they should have covered at least that much square feet to get an accurate track line).

Then it was the second group's turn outside and at that point, the GPS unit had been in the cold for more than 20 minutes and the temperature had dropped another couple of degrees. The GPS unit did not like that and got a bit wiggy on us.

And that was unfortunate because this particular group had some creative ideas for their drawings.

The first was a "heart" and the group organized their members in positions around the key turning points to make a symmetrical drawing.

Unfortunately the GPS unit had a different idea.

That stray line was definitely not ground covered by the group.

Then they tried to draw an eye ball, and again positioned group members at different points to make it more accurate.

And although the drawings did not turn out quite as planned because the darned GPS unit wasn't cooperating, all the kids seemed to get into the drawing portion of the class. And I assured my second group I'd fix up their heart drawing later because it should have worked.

When we were inside warming up after our drawing, I talked to the group about how the technology behind the GPS unit worked.

HowStuffWorks.com has a very informative piece about GPS units that was a helpful resource in explaining this stuff to the kids. Here's a synopsis:

When people talk about a GPS, they usually mean a GPS receiver. The Global Positioning System (GPS) is actually a constellation of 27 Earth-orbiting satellites (24 in operation). The U.S. military developed and implemented this satellite network as a military navigation system, but most are now open for public use. Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles, making two complete rotations every day. The orbits are arranged so that at any time, anywhere on Earth, there are at least four satellites "visible" in the sky. A GPS receiver's job is to locate four or more of these satellites, figure out the distance to each, and use this information to report its own location. This operation is based on a mathematical principle called trilateration. In order to make this trilateration calculation, the GPS receiver has to know two things: 

* The location of at least three satellites above you 

* The distance between you and each of those satellites The GPS receiver figures both of these things out by analyzing high-frequency, low-power radio signals from the GPS satellites. 

Better units have multiple receivers, so they can pick up signals from several satellites simultaneously. Radio waves are electromagnetic energy, which means they travel at the speed of light (about 186,000 miles per second). The receiver can figure out how far the signal has traveled by timing how long it took the signal to arrive.

Then we played a game about the basics of mapping (the less interesting stuff to 21st century kids that included longitude, latitude and the "old fashioned" way of creating maps), before downloading the kids' drawings and printing them out.

It turned out that I did not have time at the class to fix the "heart" drawing (which required me to draw the missing line on the track using Google Earth) so I just took care of that so those kids could see that it really was a great drawing idea.

Next time we'll stick to the GPS drawing in warmer temperatures. I think the kids, and my GPS unit, will appreciate it.