Day’s Verse:
Even youths grow tired and weary,
and young men stumble and fall;
but those who hope in the LORD
will renew their strength.
They will soar on wings like eagles;
they will run and not grow weary,
they will walk and not be faint.

Isaiah 40:30-31

Have you noticed how it’s impossible to pin down the actual temperature? You put a thermometer outside (on the north side of the house, under cover, as recommended by people in the know) and it tells you a number. Then you check online, and your local weather station says something perhaps 5° off from your thermometer. Then you get in your car and drive away, and your car tells you a temperature — which is immediately contradicted by the bank’s thermometer and the thermometer in the health club across the street, neither of which agree with your car, the Internet, or your home thermometer. So what is the real temperature?

Elevation has a similar elusiveness to it. People on bikes love to boast to other people about their “total ascent” — number of feet climbed over the ride. Some GPS devices even have a nifty feature that tells you total ascent as you ride, so you know exactly how many feet you’ve climbed at any time. Many training plans include total elevation along with distance. So knowing elevation fairly accurately is something bike people want. My Garmin, an Edge 605, keeps track of elevation, but it’s not quite fancy enough to give me the “total ascent” option, at least not as far as I’ve figured out.

Now, the thing about a GPS is that it just can’t handle vertical changes very accurately. One time I’ll ride on a road and it’ll tell me I’m at -6 feet. The next time I ride on the same road, it’ll tell me I’m at 36 feet. This doesn’t inspire a huge amount of trust in the GPS’s ability to accurately reflect how many feet I’ve climbed.

This is where GPS Visualizer comes in. This is a nifty — and incredibly detailed — website that does all sorts of things with your GPS data. One of those things is creating an elevation profile: it will take your route and, ignoring the GPS elevation data, add up your elevation from reliable sources like the USGS. It displays the resulting elevation profile in a nifty color-coded format. You can actually choose where the elevation data comes from.

Because I’m a nerd and I love data, I decided to do a comparison of the various sources that told me what elevation I’d climbed for today’s ride. My goal was to ride about 65 miles and climb about 4,500 feet. My sources:

Results:

  • SportTracks: +4099 ft / -3978 ft
  • Plus 3 Network: +5162 ft / -5989 ft (the blue line is speed, the grey shaded area elevation)

  • GPS Visualizer from GPS directly: +6243 ft / -6182 ft
    Elevation profile - Garmin GPS data

  • GPS Visualizer using USGS NED data: +5246 ft / -5263 ft
    Elevation profile - USGS NED Database

  • GPS Visualizer using SRTM1 data: +7267 ft / -7279
    Elevation profile - NASA SRTM1 Database

So the question is: Did I meet my goal? If I wanted to impress people, I’d go with the SRTM1 results — 7,000 feet of climbing in 63 miles is nothing to sneeze at! But then, SportTracks gave me a fairly modest 4,100 feet of climbing, not a number that would raise many eyebrows and which is, in fact, under my climbing goal. Who to trust?

Frankly, I trust my legs. They tell me that I went up a lot of hills, more than 4,000 feet but probably not 7,000 feet. That gives me an upper and lower bound, but 4000 ft < X < 7000 ft doesn't narrow it down much. Personally, I'd be inclined to go with around 5,200 ft. But if there's some way to actually figure out the real number, I'd sure like to know. Then again, it may be like temperature: Measurable, but ultimately unknowable.

2 thoughts on “Elevation, Elusive Elevation

  1. Not sure if you know, but there is a free SportTracks plugin to pull elevation data from the SRTM data sets if you Edge is bogus.

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