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Why GPS Track Recording Can Be Inaccurate

You may find with Gaia GPS that your recorded tracks are not the same length as the track lengths displayed on other iPhones, Androids, GPS devices, maps or trail markers. Even the most recent models of iPhones and Androids, which have better GPS chips, can easily vary by 5-30% from other readings. 

Despite the fact that Gaia GPS is calibrated to poll the GPS for maximum resolution and accuracy, the following factors confound estimation. We continue to explore ways to improve estimation of distance from GPS data but there are limitations that will always exist. 

1. Trail Markers and Maps are Measured in Multiple Ways - Trail markers and maps use multiple methods to determine the length of trails. The most accurate measurements are done with a measuring wheel, which is rolled along the trail and has a revolution counter. Even with a wheel there is plenty of opportunity for error. The wheeler must be careful that the wheel does not slip, and wheelers have to decide which parts of trails to measure when there are difficult scrambling sections or two ways around a tree in the middle of a trail. 

Trails are also measured using maps estimations, which can be very inaccurate, or using GPS devices, which vary in resolution. 



2. Your Device's GPS Accuracy - GPS accuracy varies across iOS and Android devices, the newer the device the better the estimation. If you use a newer device, you will likely have a more accurate reading than a friend that uses an older one. Additionally, thick tree cover and cloud cover, or even tall buildings, can interfere with your device's connection to GPS satellites.  

3. Inaccuracies Accumulate Over Time -  When a computer, like an iPhone, Garmin, or Android records GPS locations, each location or track point, has a small amount of possible error. These marginal errors add up over time, so your tracks are likely to be recorded as longer than you expect.   

 
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4 Comments

  • 1
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    Erik Turner

    I've been in the habit of uploading tracks to Strava after using Gaia to record them. Strava must apply some smoothing / post-processing to the tracks, which usually then aligns much better with what trip planning, and trail markers etc, show as the elevation / distance of the track. Does Gaia do any post-processing to tracks? Maybe it could be done only if you check a box to avoid those who don't want it?

    I would assume it's just a smoothing function which takes out alot of the "left" / "right" jags from the data.... seems like the closer to perpendicular to the existing heading a single segment is, the harder it could be smoothed back... 

  • 1
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    Andrew

    I guess the main answer is that Strava does a really good job. Check out this tech that they built that underlies what you see: http://labs.strava.com/slide/

    We are doing some stat calculation improvements coming up, and we use some decent algorithms for smoothing lines... which I could see us tweaking further... but I won't promise to match Strava's tech in this area yet.

    Andrew Johnson

    Founder, Gaia GPS

    Edited by Andrew
  • 0
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    Tom Cal

    When recording tracks in Gaia, is there a way for the user to control the sampling frequency that points are recorded, using a set time, and/or distance?

    How often, measured in time and/or distance, does Gaia record points?

  • 0
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    Ashli Baldwin

    Hi Tom,

    No, this is not currently possible, but please feel free to vote/comment on a related feature request here: https://help.gaiagps.com/hc/en-us/community/posts/210604888

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