How to measure a climb (Page 2)

Forum guidelines BT super discount
General Discussion Triathlon Talk » How to measure a climb Rss Feed  
Moderators: k9car363, alicefoeller Reply
 
 
of 2
 
 
2009-07-11 9:00 AM
in reply to: #2259407

User image

Expert
1123
1000100
Falls Church, VA
Subject: RE: How to measure a climb
marmadaddy - 2009-07-02 8:24 PM
PennState - 2009-07-02 7:34 PM
breckview - 2009-07-02 7:29 PM
PennState - 2009-07-02 5:21 PM
breckview - 2009-07-02 7:19 PM There's a little checkbox, "__ Show Elevation" that when checked computes the total ascent which on that ride was 1401 feet.


Problem is that there really is no 'accurate' way to measure elevation gain.

GPS is pretty inaccurate as is internet software.
Altimters that work on barometric pressure are thought to be a bit better, but no perfect answer... actually the real answer is it's a FRACTAL.
The Mapmyride and BT Route Tracker websites both use an elevation database that is by far the most accurate measure. For my rides it's very accurate because we have USGS benchmarks at the top and bottom of all the climbs to compare against.


Breck, the BT route tracker will give you completely different results if you ask it to re-calculate. Not exactly accurate.



The Reset Elevation button is also there for routes that have been uploaded from Garmins or GPX files. It forces a query of the USGS database for every lon/lat pair in the file.

Depending on the number of datapoints in a route and one's internet connection speed, this can take a long time. If you get disparate values from the same dataset, it's most likely due to a connection issue.

ETA:

The error breckview mentions will not be present in the next version of the route tracker. That was a design flaw I've since learned how to avoid.

For the record, the USGS dataset was created via radar on a Space Shuttle mission. The reason that moving a datapoint gives you a different value is that the elevation value for the new location is retrieved from the USGS database.


ah.. o.k. I will now be using reset elevation on mine.

First one I did looks awesome, and kind of funny how different it is compared to the garmin data. 

2009-07-11 9:15 AM
in reply to: #2277258

Master
2460
20001001001001002525
Subject: RE: How to measure a climb
breckview - 2009-07-10 6:29 PM
Tripolar - 2009-07-10 5:06 PM Or am I way off base?
Yes. Imagine a 100 stairs, each one foot tall. If you measure in 100' resolution the gain will be 100'. If you measure in one foot resolution again the gain would be 100'. Now set a 4x4 across each stair. Measuring at 100' resolution is still 100' in gain. But if you measure at 4 inch resolution, the gain becomes 1033 feet. If you measure at a microscopic resolution, you'll go up and down each molecule on the surface of the 4x4 and the gain is higher still. The reason why a garmin is more accurate for a long sustained climb is that error is only introduced when the elevation mistakenly drops on a constant climb. Assuming a linear 10% slope for 5 miles. The elevation should be higher each time the garmin takes a sample. As long as it is higher at each sample, the only elevation samples that matter in computing total gain are the first and last. Compare this with a perfectly flat route at sea level. The only elevation sample that doesn't result in false climbing gain is a perfect 0 feet.


I differ somewhat with this above post.

I agree with the previous poster that the differences and vairations in measurement become very small, and probably insigificant at a certain point.

I see your point about resolution, and that part I guess is correct. For example if we unfolded your intenstinal villi and used microscopic resolution, we could get your intestinal length to probably double or triple its gross length, because we're going up and down all those micro hills. That I agree with.

However, remember that when biking or running, your are NOT doing this at the microscopic level. You are taking footsteps or rolling across terrain that is measured in FEET, not microns. As long as your GPS resolution is down to close or half the smallest increment (your footsteps or wheelbase), you will not suddenly improve your distance by reducing the measurement distance.

So in summary, a GPS accuracy of 1-3 feet should not be significantly changed for runners/bikers by reducing the GPS accuracy to smaller increments. Unless you suddenly shrink into bacteria-size and started running at 5 micron intervals!
2009-07-11 11:04 PM
in reply to: #2259967

User image

Master
2372
20001001001002525
Subject: RE: How to measure a climb
PennState - 2009-07-03 7:16 AM All good points Breck, but again what I was trying to explain was that it is an execise to infinity. By this I mean that the smaller the measurement distance between each measurement point (and no 3 feet isn't that small) the larger the elevation gain will be recorded... ie; it will account for each little pebble of gain in the road.



This isn't true.  It would be true if nature was equivalent to a pure mathematical fractal, but in nature fractals have bounds, both high and low.

There will be a lower limit under which the elevation changes are no longer fractal. 

(I did natural fractals for my master's thesis.  Yes, I am a geek.)
New Thread
General Discussion Triathlon Talk » How to measure a climb Rss Feed  
 
 
of 2