Elevation Confusion

“You don’t need a weatherman to know which way the wind blows.”
- Bob Dylan, “Subterranean Homesick Blues”

Any runner will tell you that it’s incredibly easy to realize when you are running into a headwind, or whether you are headed uphill or downhill. You can also be relatively certain about the distance you’ve traveled, especially if there are mile markers on the road or if you’re wearing a GPS.

But how high are the hills you climbed? And how much climbing have you done over those miles you’ve measured? Answering those questions sometimes requires an advanced degree – and even then, you’re probably not certain of your accuracy.

Case in point: prior to our Big Sur Marathon preview article, we attempted to quantify the differences in climbing between the traditional course that features Hurricane Point and the out-and-back course that includes the rolling hills of Carmel Highlands twice. Researching the subject was one of the most mind-boggling ordeals we’ve experienced lately.

We started with the elevation profile on the race website, which indicated that the total climbing over the new course was 2400 feet. The data came from a Naval Postgraduate School scientist who used a USA Track and Field website mapping tool. He explained to us that the elevation information is stored in US Geological Survey NED database tables, and then extrapolated over a known distance (in this case, 26.2 miles).

Another tech-savvy friend of ours used his Garmin GPS watch for two previous Big Sur Marathons as well as this year’s modified course, and shared with us his GPX files, which plot latitude and longitude points alongside data from the USGS database. His readings showed approximately 1750’ of climbing for the standard course, and 1630’ on the new course. He also explained that handheld devices rely on triangulation of satellites in the “GPS constellation” for accurate position reporting, and visibility of a 4th satellite to add the elevation component – and it was right around here that our heads started to spin.

That’s not all, however … because our friend’s data from his two Big Sur Marathons on the standard route also deviated by about 100’ from each other. We asked him to explain, which opened the floodgates to a whole world of fractals, calibrated barometric variables and fluctuating weather permutations, smoothing algorithms, and numerous other scientific conditions that we couldn’t begin to comprehend. Suffice it to say that any elevation data you see in course profiles is going to have a degree of uncertainty – in some cases, quite a significant amount.

Fortunately, none of this distracted from the task at hand on race day for our tech-savvy friend Brian Rowlett, who ran 2:53:05 for 15th place overall last Sunday, using his Garmin GPS watch as usual. It’s worth noting that his time this year was virtually identical to his personal record from the standard course, even though there was (according to his watch) slightly less climbing this year. External conditions such as wind and air temperature might have made an impact as well, but honestly, who the heck really knows?

All that the two of us learned for sure in this process is that we like to stick to simple considerations like knowing which way the wind is blowing. From now on we’ll just refer to our local marathon as a hilly, challenging course, and leave the elevation data for the scientists to figure out.

Purchase The Running Life Book via PayPal button on right sidebar.

0 comments:

  © Blogger template The Professional Template by Ourblogtemplates.com 2008

Back to TOP