Different climbing profiles same route

Dwight Follien's Avatar

Dwight Follien

07 Apr, 2018 01:20 AM

Hello,

I have a question... first, I'm really new at this. I'm mapping a bike ride
event and want to know how much climbing there is on the route. There are 3
routes but I'd like to deal with the long route first

I have two map versions of the long route. One is a continuous line and the
other is broken up into sections because there are permits and written
permission needed to ride through sections of the route.

The one line map's profile has over 5200 ft of climbing it seems from the
expanded Elevation Profile-
 https://sartopo.com/m/PK6H

Here is the other map of same route going in same direction but divided in
sections as opposed to a single line- https://sartopo.com/m/9JNJ
This map when adding up each section's climbing total from each section's
expanded Elevation Profile the total is over 7200 ft of climbing.

I'd just like to know why there is a 2000 ft difference and which one is
more accurate. It may be something I did when doing the mapping, like I
mentioned I'm new at this and a novice when it come to anything on a
computer.

Regards,
Dwight

  1. Support Staff 1 Posted by matt on 07 Apr, 2018 07:19 PM

    matt's Avatar

    That is a long route.

    When I compute the elevation profile, I have to use a fixed number of points; the distance between those points is called the sampling interval. The small profile relies on Google Maps elevation data, while the large profile relies on my in-house data. Google won't let me pull as many points, so the sampling interval on the small dialog will be larger (aka less accurate).

    For performance reasons, I still only request several hundred points when building the large profile dialog, so breaking a long route into chunks will give you more accurate numbers (400 points per chunk instead of 400 points total). 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.

    Depending on how carefully the line is drawn, you don't want too small of a sampling interval, or you'll pick up artifacts from inaccuracies in the line (for example if a GPSt rack on a sidehill appears to be constantly zigzagging up and down hill). A perfectly accurate number is complicated, and for a lot of trails, somewhat subjective.

    In this case 7200 is probably the right number - the first map has a sampling interval of 850', which is way too large.

  2. 2 Posted by Dwight Follien on 10 Apr, 2018 07:00 PM

    Dwight Follien's Avatar

    Thanks, Matt! Breaking up the routes into sections does make sense to get a
    more accurate climbing total.

    Cheers,
    Dwight

  3. matt closed this discussion on 10 Apr, 2018 09:03 PM.

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