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Discussion Starter · #1 ·
Does anyone have experience calculating total elevation gain for various rides, especially as related to the statistics provided by Topo USA 6.0? I am the coordinator for the upcoming 8th annual Country Coast Classic century out of Cambria, CA. I have used Topo USA 6.0 to describe the route. The program gives very accurate total ride distances, and accurately depicts the elevations along the route (summits, etc.). But the calculated 'total elevation gain' is roughly twice what my cycling buddies get with their on board computers (one a VDO) when they ride the course. The on board computers do some averaging based on atmospheric pressure changes, I'm sure. What data should I trust? Or, what is the source of data others use when describing a route to prospective riders?
 

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Rodie Persona
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I could go on for days about how these types of programs calculate elevation using the under lying elevation data (typically USGS 10m or 30m digital elevation models). I am a geographer by education and profession and can explain more about elevation variability if you would like to know more. My masters thesis deals with this very subject. Assuming you want the short answer, bottomline there is a good deal of uncertainty.

I would suggest getting a GPS, a Garmin Edge would work, and drive the route; as well as calculate the elevation with Topo USA. If you want to get even more anal about it, calculate the same route with National Geographic TOPO. Take the values and average them.

I have found NG TOPO to be about 10% under with distances, though a bit better with road routes as I can more accurately map straight lines on streets.
 

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Discussion Starter · #3 ·
Topo USA 6.0

The version 6.0 calculates distances quite accurately. It is not necessary to create a series of straight line segments. I just click on a start point (along some state hwy or county road) and an end point, and the software traces the route along the shortest asphalt route. I can then add "vias" which cause the route to go along the roads I plan to ride, and the sw automatically traces that route, start to finish. Distances compare very well with my cycling computer and with Google Map.

It's only the resultant cumulative elevation gains that vary from the computer on the bars. I'll have to borrow my friend's Garmin and drive the course to get another set of data.

All of the methods are going to do some amount of averaging. i.e. if you ride an absolutely pancake flat course on a glass surface, there should be no cumulative elevation gain. But what if you are riding on cobbles? The bike might bounce up and down a quarter of an inch every 2 inches. A very sensitive measuring device could report a 660' cumulative elevation gain over a mile (and a 660' cumulative elevation loss) due to a quarter inch rise every 2 inches. That's a pretty extreme example, but I think it illustrates the problem. My friend's VDO that takes a sample every 15 seconds will miss many (very small) elevation changes.
 

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Completely ignorant on this, but getting interested. What elevation gain do these programs and bike-mounted computers show—total feet climbed, or total feet climbed minus the feet climbed 'again'? In the sketch, would total elevation gain shown be 270 feet or 200 feet for someone climbing from the 0 to the 200 mark?
 

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I've used the Topo USA program a lot to reproduce maps of some of my favorite rides (events) and you are correct in that this program overstates elevation changes.

The reason I came up with is that it calculates on the actual topo contour data lines and does not take into account the fact that roads smooth out many of the minor undulations in the terrain.

What really brought this to my attention was a route going over a huge gorge that I knew had a bridge. The program showed the route going to the bottom of the gorge and back up, which would have been an impossible climb.

I'd have to agree with MTBMaven that a GPS device would be much more accurate.
 

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Discussion Starter · #7 ·
Aha! Now I get it. All rural roads in hilly country use successive cuts and fills to smooth out the contours, but the sw doesn't know about this. I'm going to have to get a GPS unit. Thanks for your input.
 
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