Yosemite

EVERY YEAR, we make a 16 mile pilgrimage to the top of Half Dome, a barren peak in the middle of Yosemite National Park. I took a GPS device on the trail in 2007 and realized six months later that there was a USB port on the handheld that would allow me to extract the data. Naturally, I was inclined to see if I could get the points to line up on some digital elevation models garned from the USGS.

Befuddled by the passage of time, my GPS told a harrowing story of me flying into the sky and under ground at random intervals. Then I realized that GPS altitude accuracy is not so good and wrote a routine to tie the points to the ground — it's OK, even Google Earth resorts to these measures. Otherwise, the geographic registration of the points is pretty good.