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en:help:1.4:landmarks:statistics [2014/11/02 21:51]
alpinequest [Tracks statistics]
en:help:1.4:landmarks:statistics [2017/09/12 11:21]
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-<​sub>​[[en:​help|Online Help]] > [[en:​help:​1.4|AlpineQuest 1.4]] > [[en:​help:​1.4:​landmarks|Landmarks]]</​sub>​ 
-====== Statistics on tracks ====== 
  
-===== Gain and loss ===== 
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-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. 
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-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. 
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-In order to compute these values, it's important to define more precisely what means "along the track"​. 
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-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**. 
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-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. 
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-At then end, the "​perfect"​ gain definition would be something between these two last one. 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. 
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-{{:​icon_help.png?​nolink}} You can disable or increase the default noise reduction. In the statistics settings section, click on the ''"​**Edit**"''​ button {{:​icon_01.png?​nolink}},​ and change the ''"​**Noise reduction**"''​ setting {{:​icon_02.png?​nolink}}. 
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-{{ :​en:​help:​1.4:​landmarks:​statistics:​settings.jpg?​nolink }} 
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-Here is the effect of the noise reduction on a track profile and gain computation:​ 
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-  * On the left, the noise reduction is disabled. The profile displays the unmodified jagged and spiky altitudes {{:​icon_02.png?​nolink}} (mostly due to the GPS inaccuracies),​ resulting in a high gain value {{:​icon_02.png?​nolink}} (+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). 
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-{{:​icon_help.png?​nolink}} The first gain definition given above, gives an approximate under-estimation value of +1600m for this same track. 
- 
-{{ :​en:​help:​1.4:​landmarks:​statistics:​noise-reduction.jpg?​nolink }} 

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