Differences in elevation gain / whole track versus split up track

rk219's Avatar

rk219

18 May, 2018 03:20 PM

Hello. I have a question concerning elevation gain and loss. I understand the differences between the "Profile" and "Terrain Statistics". This rather has to due with elevation gain and loss when I combine a series of tracks into one long track. I suppose this may have to do with sampling?

The track in question is the Foothills Trail in South Carolina. It is about an 80 mile hike. I did this over 6 days (and 6 different tracks). When I examined each of the 6 individual tracks and added them all together my total distance was 81.97 miles, Profile elevation gain is 18,032 feet and my terrain statistics gain is 20,597 feet. I get why those are different.

However when I combine all the tracks into one using my GPS software and then upload it to Caltopo my distance is 82.03 (negligible difference), my profile gain becomes 10,730 and my terrain statistics gain becomes 12,844. This total track has about 13,000 points.

This is a big difference. Which one is more trustworthy? The sampling intervals on the single tracks seem to range from 200 to 250' and the sampling interval on the combined track is 1,444'.

If I try to resample to something like 200' feet then it dramatically lessens the total mileage while slightly raising the elevation gain. Also, the final sampling interval is somewhere around 1200' instead of the 200' that I typed in?

Thank you.

  1. Support Staff 1 Posted by matt on 20 May, 2018 02:13 AM

    matt's Avatar

    Yes, it's the sampling interval. See http://help.caltopo.com/discussions/general/2361-different-climbing...

    Not sure what you're getting at with the final paragraph, but if you are actually resampling the line (right click -> modify -> resample), that has no bearing on the elevation profile. I use 200-300 points regardless of whether it's a straight line with just a start and and end, or a GPX track with a thousand points.

    With a pro-level subscription, you can set your own sampling interval (resample link at the top of the dialog) to get more accurate gross gain/loss numbers, but be careful about using super-small intervals like 25' or 50' unless your line is really carefully drawn, or it will lead to overstating the elevation gain.

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