Hacking Geocaching

If a gadget or device penetrates the consumer market well enough, it will eventually be incorporated into some sort of game activity. GPS is no different, and because GPS can be used to pinpoint locations, making

a game out of getting to locations marked by others was an obvious evolution. Before any games could spawn from GPS, however, accuracy had to increase. This chapter examines geocaching, after a little history of the accuracy of GPS.

GPS Accuracy

For years, GPS wasn’t available to the likes of you and me; it was purely military-only equipment. Back then, GPS receivers were too expensive for most people. The price eventually dropped, but GPS still had limited appeal, and its main users were sailors and hikers. What GPS needed to become popular was an injection of accuracy, and this is exactly what happened on May 1, 2000, when former President Bill Clinton removed the deliberate error contained in the GPS signal up until then.

This error, known as Selective Availability (SA), degraded the signal that consumer units could pick up. Selective Availability meant that 95percent of the time the position shown on a GPS receiver was supposed to be off by 100 yards or less, while for the other 5 percent of the time the error might be even greater, or there might not be any error at all! You never knew. Basically, the 100-yard error meant that you could only reliably plot your position within a circle 200 yards in diameter, as shown in

Figure 11-1.

chapter

in this chapter

˛What is geocaching?

˛A typical geocaching trip

˛Tips on finding a geocache

˛How to power your electronic devices while on the move

˛Protecting your gear while on the move

256 Part IV — Playtime

Selective Availability error plotted over time (1 plot per second)

FIGURE 11-1: Uncertainty in position of 200 yards

This really wasn’t the level of accuracy demanded by the consumer and it only appealed to people to whom navigation was important. With the SA signal degradation removed, accuracy instantly increased, and you could now plot your position reliably within a circle 20 yards across or less, as shown in Figure 11-2.

Because this massive improvement in accuracy was signal-related, it didn’t require users to buy new receivers in order to benefit — most users had receivers capable of handling the more

accurate coordinates. (Some units, however, did have a feature that rounded down the accuracy internally to reduce the effects of SA, and these units did this with data from the non-SA signal too, meaning that these units were still as inaccurate as before.)

With increased accuracy, GPS now took almost all the guesswork out of navigating. As long as you had a GPS, a clear view of the sky, and an unlimited supply of batteries, you could get an accurate fix on your position anywhere in the world, accurate to within a few yards.

The modern era of GPS gaming was born.

Chapter 11 — Hacking Geocaching 257

Without

Selective

Availability

FIGURE 11-2: 20-yard uncertainty

The Birth of Geocaching

On May 3, 2000, someone placed a container filled with treasure (well, not really “treasure” in the true sense of the word — more like a few cheap trinkets) just outside of Portland, Oregon, to celebrate the removal of SA. Within three days, the “cache” had been visited twice.

The first to find the container was a chap named Mike Teague, and he decided to create a website to document and publish the location of these containers filled with goodies. These locations were also posted on the sci.geo.satellite-nav newsgroup.

But the sport still didn’t have a proper, catchy title. This had to wait for someone else to get involved. In July of 2000, Jeremy Irish came across Teague’s website and became hooked on the sport. Irish approached Teague with ideas for the redesign of the website, along with ideas of logging the finds online, mapping the finds, and creating an easier way for newcomers to the sport to find and place these containers. Irish also came up with a new name for the sport, and so the term geocaching was born. The treasure-filled containers were renamed geocaches, the participants were called geocachers, and all of a sudden a lot of people became interested.