So, your Garmin is most accurate for Strava hey?

[FlandersZA]

It has been said that using a garmin device or proper GPS unit for recording strava activities is more accurate than using a mobile phone. Recently some anomalies cropped up on my rides where some activities were recorded very accurately and others not so much.

 

I use a garmin e-trex10 handheld device I keep in my pack for the mtb and other things. I had recently re-calibrated my cateye which is now as accurate as I can get it and my GPS unit’s readings were corresponding very closely with strava and the cateye. I’m a bit pedantic about this sort of thing so I even went and measured in comparison using satellite data to ensure all was as it should be. Everything was in order except for when I rode at Northern Farm. Every NF ride I do, my strava under-reads by 1km or so when I do the red/black route. This sort of inconsistency bugs me in a way that I just need to get to the bottom of it to try and understand. The folks I ride with were getting closer strava distances to my cateye using the iPhone and android app on their phones than I was using my garmin. The garmin e-trex 10 has a setting where you can determine the frequency at which the device records a point in time and mine is set to its highest setting or “most often” so I know I am getting the most accurate readout the device offers. As it turns out, “most often” may just not be often enough.

 

I have figured out what is happening. On a path with relatively straight lines or minimal curves, the recording goes without a hitch but as soon as you throw in intricate curves and bends such as the windy sections near the river at Northern Farm, it becomes apparent that the garmin is either a.) not recording enough points per x amount of time to create an accurate curve or, b.) the conversion process to GPX, whether it be on the device itself or between the device and strava is causing a loss in accuracy. My findings:

 

Garmin e-trex 10 - NF track:

http://img.photobucket.com/albums/v648/flannahs/nf_garmin_eTrex_zps8297495e.jpg

 

As you can see, the recorded path is quite jumpy and cuts out actual distance travelled. This all adds up, resulting in under-read. I suspect the faster one goes, the worse the result will become – and I sure am no racing snake. I thought that maybe this particular unit was possibly not best suited to this type of activity (although why wouldn’t it be? It’s a purpose-built GPS unit) so I compared with the same section done by someone using a garmin edge 800. Result:http://img.photobucket.com/albums/v648/flannahs/nf_garmin_edge800_zps5c1e83a1.jpg

 

Better? Debatable, but here’s where the kicker comes in. The next image is a track recorded on a phone using the android strava app:http://img.photobucket.com/albums/v648/flannahs/nf_android_zpsace998e3.jpg

 

Note how the curve follows the actual singletrack a lot closer than either of the garmin devices.

 

iPhone strava app:http://img.photobucket.com/albums/v648/flannahs/nf_iphone_zps3d4ad531.jpg

 

It seems to me that where strava and distance is concerned, the mobile phone apps may actually be better than a purpose-built garmin device – depending on the complexity of the track recorded. As far as average speed and elevation goes, I believe that the garmin devices are far more accurate. The garmin e-trex 10 does not use a barometer to calculate elevation but using tracks I have compared with satellite imagery, it seems to accurately compare. Average speed and general speed readouts appear most accurate on the GPS devices. I have tested in a car and it’s even possible to see the built-in safety margin the car manufacturers give car speedometers by comparing with the GPS unit. From what I can see, the mobile phone apps are most inaccurate with average speed, followed by elevation gain in comparison with the garmin units.

[ChUkKy]

How frequent is your Garmin recording, every second, 5 seconds or what?

Those lines look very straight to me

[Tankman]

So you did not win the Strava KOM?

[WIPEOUT 1000]

My experience with Garmin is that the vertical accent calculation becomes particularly dodgy in bad weather.

[FlandersZA]

How frequent is your Garmin recording, every second, 5 seconds or what?

Those lines look very straight to me

 

I don’t know how often it records in actual numbers. This garmin unit uses these terms: “least often”, “less often”, “normal”, “more often” and “most often”. It is set to “most often”. As you can see though, it isn’t wildly different to the garmin 800’s track.

 

 

 

So you did not win the Strava KOM?

 

LOL! The one single KOM I got once without even knowing it was a segment has long since been pipped. My strava addiction comes from other things.

[nickcza]

It could just be the viewer you are using, are those screen shots from Garmin Connect?

For example, if you open the same track in the Garmin Connect "Player" the resolution will get even worse.

Try export the track and open it in another app, such as GPX Editor.

[FlandersZA]

My experience with Garmin is that the vertical accent calculation becomes particularly dodgy in bad weather.

I’m sure this is due to batrometric conditions being affected. My device doesn’t use a barometer to calculate the elevation but rather map data.

[Long Wheel Base]

Interesting. I have a garmin edge 500 and i upload to both strava and garmin connect and i have a discrepancy between those two programs when loading from the same device. I upload exactly the same to both programs and this year so far strava has me having ridden 25.45 km more than garmin connect. That's with just under 6000km done. Iv also noticed that sometimes my tandem partner has different strava segment times than me and he also has an edge 500.

[Super Sywurm]

Maybe its not the Garmin, but the rider who can't stay on the track!?

[FlandersZA]

It could just be the viewer you are using, are those screen shots from Garmin Connect?

For example, if you open the same track in the Garmin Connect "Player" the resolution will get even worse.

Try export the track and open it in another app, such as GPX Editor.

 

 

These are screenshots directly from strava at the same zoom level.

[Guest Sam Blake]

Maybe its not the Garmin, but the rider who can't stay on the track!?

 

Yeah, top photo was actually taken by Kevin Evans.

[lechatnoir]

do those etrex units have a setting for interval recording? the point density along lines will dictate how 'windy' the curves are. IIRC there are two settings; one for distance between points, the other for TIME between points. The downer is that when you set the point density along the line to be too high, you can store fewer/shorter tracks (more data is stored)

[Skinnyone]

You will get this with ANY GPS device...basically its comes down to how many satelites the unit "sees" at any given time and the accuracy can vary by up to 10meters at any given time.

 

I play around with auto pilots as a hobby and this can often cause a "fly away" situation where the GPS is now reading that its 10 meters away from where it should be and moves to that spot...can be tuned to a point but it boils down to how much money do you want to spend and how much weight you want to carry on your bike or model aircraft...

['Dale]

That's some subtle stuff there hey

[DIPSLICK]

THIS IS WHY I PREFER TO USE ONE,

 

its the story of a broken watch twice a day its on time

 

if the one is better than the other, or it serves its purpose use it, then again i only use strava for my own idea of how my riding is going,

i never alternate between the 2 because there is a difference(ok ok i use the one that makes me the fastest)

[FlandersZA]

do those etrex units have a setting for interval recording? the point density along lines will dictate how 'windy' the curves are. IIRC there are two settings; one for distance between points, the other for TIME between points. The downer is that when you set the point density along the line to be too high, you can store fewer/shorter tracks (more data is stored)

 

Trevori, I think you are onto something here! I just discovered that the eTrex does indeed have options for both time and distance. I will try using distance at a smaller measurement and see if it makes a difference. Maybe all I have written in the OP is BS. Would be interesting to know if the edge units have the same?

 

I will post my findings when I do my next ride there.