[closed] tracks seem to overestimate distance

[jordanchap]

I've been using your app for a while now. Love it. But I recently went backpacking with my brother and his iphone with some other app. His was always showing shorter distances than me and it was quite a difference. Also I compared mine to known trail lengths and mine was always higher than it should have been. Is this a known problem?

[Psyberia-Support]

Hi,
No such problem has been reported yet.
Note that AlpineQuest impacts the elevation differences on the total distance (the detail is given in the stats panel). Even if it reflects the reality, this is not usually done by other apps.
I recommend you to check your tracks using online tools to see what's computed there, like http://www.gpsvisualizer.com (select 'elevation profile', the distance is given in the X axis) or http://www.visugpx.com/ (in french but with a lot of stats). You need to export/convert your recorded track in the GPX format first.
Let me know what you get there.
Best regards

[jordanchap]

Ok so I did that and the distances are fairly similar with what aq gives. Can you explain the differences? What do you mean by that aq adjusts for elevation where most apps don't?

Also what is the soothing and elevation threshold mean? When I change those values, it changes the distances as well.

Thanks for the help!

[Psyberia-Support]

Hi again,
When you walk 1 mile on a path with an important elevation gain, you will actually walk more than 1 mile on a flat trail. You can compute this difference based on your beginning and final elevation.
In AlpineQuest, when displaying the detail of a track, the distance takes elevation data into account. The "flat" distance is also given. You get something like that on the "Length" line:
- 15.12mi (14.98mi + ↕254.51yd) (which is 14.98mi flat mile and 254yd due to the elevations of the trail).

Concerning the stats settings:
- The smoothing allows you to "mean" elevations of few consecutive points to reduce GPS inaccuracies (GPS is quite inaccurate concerning elevations),
- The elevation threshold allows you to only take account the elevation changes when it's cumulated difference is bigger than this threshold. This is common technique used to compute a more precise cumulated elevation gain (otherwise it's much over-estimated).
If you change the elevations, then the total distance may also change a little due to the use of elevations as explained before.

[jordanchap]

Thanks for the help. That makes a lot of sense.

Secondary question, are there phones that have better gps signals than others? My lg ls720 has usually gotten about 39 feet on most backpacking trips I've done.

[Psyberia-Support]

Yes the signal can be impacted by many factors including the brand/quality of the used GPS chip, the place of the chip within the device and the thickness of the plastic or material of the device.
Also, the current weather and the place where is stored the device during the tracking are very impacting.
Note that various accuracies are reported by devices, up to few meters/feet, but the GPS system only guarantees a 10m (~33 feet) accuracy, so 39ft is ok, but better accuracies are usually reported by the devices.