Tracks statistics

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 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 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 a no gain.