How well do you trust your Garmin's distance measurement in the woods?

NorthCascades
NorthCascades Posts: 10,970 Member
in Fitness and Exercise
https://connect.garmin.com/modern/activity/3866173895
https://www.wta.org/go-hiking/hikes/mount-forgotten

Normally I don't care about this kind of discrepancy. I realize that good distance measurements are hard, and it's not like anybody is paying my by the mile. In this case, I'm trying to make a hard decision, and knowing how far I walked yesterday will be helpful.

My watch said 7.8 miles at the summit, and 15.9 when I got back to my car. I would be more suspicious if it thought the way up and down were wildly different lengths, but that's as close to perfect as you get.

I spent some time with a topo map, WTA's 4,300' of elevation gain is for the trip up, but doesn't include the way down. So the Garmin is closer to the truth as far as elevation goes.

It would be strange for their guide to include elevation but not distance to the summit. There the Washington Trails Association and you leave the trail to get to the summit, so that section might well not be included in the total.

I got 36,000 steps from the trip. It was a lot of woods, a broad canyon, and some gullies, all places where GPS tends to struggle.
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Replies

  • Duck_Puddle
    Duck_Puddle Posts: 3,224 Member
    edited July 2019
    Are you using 3D distance/speed on your Garmin (I cant see your Garmin activity)? That might account for much of the difference if the website is listing a straight-line distance.

    I use a Fenix 5S plus and mine is nearly dead-on for the trails I’ve been on (vs posted maps and/or trail race listed distance). I do not use 3D distance or speed on my watch as the maps I’m using for reference are straight line measurements. I’m in New England - our terrain is heavy on the forest, light on the canyons.
  • dewd2
    dewd2 Posts: 2,449 Member
    I often run on heavily wooded rail trails to avoid the heat/sun and I noticed oddities with my pace. The pace on my watch will be off by as much as 45 seconds compared to my partner. And others in the group will all be somewhere in between. This does not happen when we are clear of the trees.

    So, no, I don't trust my Garmin 100% but for distance it is 'close enough'.
  • spiriteagle99
    spiriteagle99 Posts: 3,673 Member
    I've had issues with switchbacking trail. The Garmin will measure short because it cuts the switchbacks sometimes or if you are 5 feet above your previous location but in direct line of sight for the satellites, it will assume you haven't moved. When I had my watch set to autopause there were problems in heavy trees or rocks because if anything cut off the satellite then the watch would turn off, then turn on when it got the satellite again.
  • heybales
    heybales Posts: 18,842 Member
    I reviewed the raw data one time to see the estimates for accuracy for each GPS point read.

    It can start losing it a lot - but if trail in woods is decently straight and it gets good accuracy point read from time to time, the path and distance are pretty good.

    One trip had lots of switchbacks in thick woods though and when I saw the track, I knew the distance was going to be way off. So obvious no need to look at raw data.

    But it was backpacking - so trail distance already known.
  • poisonesse
    poisonesse Posts: 527 Member
    I've found ALL apps to be like this. Today I used MMW, a sister app to MFP. We walked 2.08 miles out, turned around walked 1/2 way back, left the trail to take a dirt track for .1 miles, turned around, retraced our steps to the exact spot where we left the original trail, then came on back to the truck, again following the original trail. I expected to come in at a bit over 4.16 miles. What did it give me? 3.97. lol I've had FitBit do this to me, MMW, MMF, Bartol, and a few other exercise apps. Now I just take all measurements as "approximates" rather than absolutes. ;)
  • xrunlukerunx
    xrunlukerunx Posts: 37 Member
    I just bought a Garmin Instinct (previously using Suunto Ambit2R) and found the GPS is a lot less accurate than I've encountered. Enough that I complained to Garmin and they said they would refund me. The one thing they recommended was doing a GPS soak before you start your activity (stay in the same spot after the GPS lock has been made for about 5-10 mins so the GPS gets a better idea of where you are)
  • heybales
    heybales Posts: 18,842 Member
    xrunlukerunx wrote: »
    I just bought a Garmin Instinct (previously using Suunto Ambit2R) and found the GPS is a lot less accurate than I've encountered. Enough that I complained to Garmin and they said they would refund me. The one thing they recommended was doing a GPS soak before you start your activity (stay in the same spot after the GPS lock has been made for about 5-10 mins so the GPS gets a better idea of where you are)

    That is true - you can get a lock with still 100 ft of inaccuracy or more - just means you got 3 or 4 satellites with good data streams being monitored.

    Sit for a bit and let that tighten up to 10 ft or better before starting out. Doesn't take 5-10 min though usually.
    Unless in a rough area, in which case starting to move will likely put you right back into trouble again.

    The Forerunner had a screen to view the accuracy, so I could decide when to take off.
  • xrunlukerunx
    xrunlukerunx Posts: 37 Member
    heybales wrote: »
    Doesn't take 5-10 min though usually.
    I think Garmin was just trying to be very generous with the time to make sure that I took the time to stay put for a bit.

  • heybales
    heybales Posts: 18,842 Member
    I recall people commenting they'd put their unit in window and let it start while they finished getting bottles, putting on shoes, getting keys, ect.
    Then outside with it for final minutes to tighten up accuracy, if it could be.
  • mbaker566
    mbaker566 Posts: 11,233 Member
    my garmin(vivoactive) is pretty accurate. every once in a while i get odd distances. once i was in washington state for a few min (i live in wisconsin)
    it's been accurate on the moraine trails here within .02mi
  • Marjael
    Marjael Posts: 111 Member
    edited July 2019
    I regularly run a loop through a heavily wooded trail. I can’t get a VO2max because of the trees, and I’ve noticed a 0.15 mile difference (over 4 miles) depending on whether I’m running clockwise or counterclockwise. (Clockwise is consistently the “longer” route.) I have no idea which is the correct distance, or if it’s somewhere in between - generally feel it averages out and is close enough for my own training purposes.
  • xrunlukerunx
    xrunlukerunx Posts: 37 Member
    Marjael wrote: »
    I have no idea which is the correct distance, or if it’s somewhere in between
    I usually use an online tool or website (ie create a route in Strava) to check what the actual distance is so I know how accurate a run is

  • NorthCascades
    NorthCascades Posts: 10,970 Member
    That's interesting - a consistent difference depending which way you go.
  • Marjael
    Marjael Posts: 111 Member
    xrunlukerunx wrote: »
    I usually use an online tool or website (ie create a route in Strava) to check what the actual distance is so I know how accurate a run is
    I’ve used mapmyrun to get distances for all the road routes I run, but this path is through the woods on private property in a rural area. I can pick out landmarks on satellite images but the path isn’t obvious, and I’ve even overlaid the Garmin maps of my run with the latest google maps images - each run varies pretty nominally.
  • Marjael
    Marjael Posts: 111 Member
    NorthCascades wrote: »
    That's interesting - a consistent difference depending which way you go.

    Agreed - I’ve joked that it must have something to do with running against the earth’s spin, lol.

  • TheNewKristin
    TheNewKristin Posts: 24 Member
    Duck_Puddle wrote: »
    I use a Fenix 5S plus

    I currently am rocking a 235. It's about 3.5 years old. It's still working fine - but I'm thinking of upgrading to a Fenix sometime before the new year. Do you recommend it?
  • Duck_Puddle
    Duck_Puddle Posts: 3,224 Member
    TheNewKristin wrote: »
    Duck_Puddle wrote: »
    I use a Fenix 5S plus

    I currently am rocking a 235. It's about 3.5 years old. It's still working fine - but I'm thinking of upgrading to a Fenix sometime before the new year. Do you recommend it?

    I am a girl and have child sized hands. The primary reason I got the Fenix 5s was size (given that many of then functions are also available on other models). All my other Garmins have been approximately the size of my palm. I have zero regrets.

    It has been through marathon (among many other races) training, miles of hiking and trail running all over the country, skydiving, swimming, regular workouts, biking, and whatever else I throw at it.

    I like the training data and a number of the other included features (like all day stress monitoring-which is surprisingly accurate).

    This probably the first device I don’t have any complaints about.

  • Marjael
    Marjael Posts: 111 Member
    Duck_Puddle wrote: »
    TheNewKristin wrote: »
    Duck_Puddle wrote: »
    I use a Fenix 5S plus

    I currently am rocking a 235. It's about 3.5 years old. It's still working fine - but I'm thinking of upgrading to a Fenix sometime before the new year. Do you recommend it?

    I am a girl and have child sized hands. The primary reason I got the Fenix 5s was size (given that many of then functions are also available on other models). All my other Garmins have been approximately the size of my palm. I have zero regrets.

    It has been through marathon (among many other races) training, miles of hiking and trail running all over the country, skydiving, swimming, regular workouts, biking, and whatever else I throw at it.

    I like the training data and a number of the other included features (like all day stress monitoring-which is surprisingly accurate).

    This probably the first device I don’t have any complaints about.

    I also have the Fenix 5S - I splurged on the Sapphire with the champagne metal band. Running, hiking, swimming, weight lifting, etc. - no complaints - and it doesn’t look out of place dressed up for work either. I love the thing as much today as the day I got it (Nov 2017).

    I had a couple Polar watches and the Fenix 3 before getting the 5s. Zero regrets on upgrading.
  • jjpptt2
    jjpptt2 Posts: 5,650 Member
    Interesting...

    I had read through most of this thread previously and thought to myself, "this is more particular/detailed than I care about" and went on about my running.

    Until today.
    I forgot my 935 at home, so had to use my backup 920xt today. I ran a route I had mapped out previously, that I thought was 4 miles on the dot. I was surprised to hear my garmin ticking off the miles at a much longer-than-expected rate. I got back to the car and... 3.3 miles. WHAT?!?!! That can't be right.

    I got back to my office a few minutes ago and looked at the data. Sure enough, 3.3 mile it tracked. But the mapped route was All. Over. The place. The route was basically an out-and-back, so the "back" track should have been pretty tight to the "out" track. Garmin says otherwise.

    So I checked the pre-mapped route on mapmyride - yup, 4 miles. Hmmm...

    Garmin tracks 3.3 miles, and the route tracked is significantly off.
    MapMyRide plots 4 miles.
    So n=1... I don't trust garmin, or at least I don't trust this garmin on these trails.

    w50z26uj9rbx.png
  • heybales
    heybales Posts: 18,842 Member
    Well, obviously you were going too fast for GPS to keep up!

    ;)

    During the satellite fixing, did you change screens to see the accuracy rate of where it was, even after it got a fix?

    I know usually if I start out before it's as best it can be - it never seems to get better in sketchy areas.
    Might check on 935 next time just to see.
    I like to get down to 20 ft before I start moving.

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