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Statistics on tracks

Gain and loss

The gain is an important value that helps to appreciate the overall profile of a track. A small gain means that the track is mostly flat, a high gain means you'll have to climb a lot.

Strictly speaking,

  • The gain is the sum of all positive altitude differences along the track;
  • The loss is the sum of all negative altitude differences along the track.

In order to compute these values, it's important to define more precisely what means “along the track”.

A first definition would be to only take into account the altitude differences between mountain passes and summits. If you start a hike at +150m, climb to a summit at +500m, then go back to your start location at +150m, your gain will be 350m. In practice, trails usually don't go straight forward to the summit, but will go uphill for some time, then downhill a little bit, then uphill again, etc. This first definition doesn't take all these small changes into account, and will then lead to an under-estimated gain.

Another definition would then be to take into account the altitude differences between all the locations that make the track. Now imagine a track recorded with a GPS along the sea. The GPS, having an imperfect accuracy, will record altitudes of [+1m, +2m, 0m, +1m, -1m, +2m, …]. With this small segment of 6 locations, we have a gain of +5m. With a track of 1000 locations, it would lead to a gain of more than +800m which is a very over-estimated gain, since the track is along a flat shoreline and should have no gain.

At then end, the “perfect” gain definition would be something between these two ones. In order to compute the best gain approximation, the application will first remove noises from the track (including the GPS inaccuracy) to create a smoother altitude profile, and then compute the gain based on each location altitudes.

You can disable or increase the default noise reduction. In the statistics settings section, click on the Edit button , and change the Noise reduction setting .

settings.jpg

Here is the effect of the noise reduction on a track profile and gain computation:

  • On the left, the noise reduction is disabled. The profile displays the unmodified jagged and spiky altitudes (mostly due to the GPS inaccuracies), resulting in a high gain value (+2535m);
  • In the middle, the noise reduction is on medium, which is the default setting. Most noises are removed, resulting in a much smaller and less polluted gain value (+1717m);
  • On the right, the noise reduction is on big. The profile smooth, with minors altitude changes lost, resulting in an even smaller gain value (+1634m).

The first gain definition given above, gives an approximate under-estimation value of +1600m for this same track.

noise-reduction.jpg

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