# Strava VS Trailforks Elevation?



## Legbacon (Jan 20, 2004)

I use Strava to track my riding and recently merged all my rides on to Trailforks. Trailforks consistently has more elevation gain than Strava, even though the data comes from Strava. Yesterday Strava said 25.9km, and 581m of climbing, while Trailforks said 26.0km and 732m of climbing. Anyone know which is more correct, why?


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## 411898 (Nov 5, 2008)

None of these readings are completely accurate since our GPS units (public use) do not continuously refresh. The more often a GPS unit refreshes your location as you go, the closer it is to being accurate but it will never be 100% accurate. If you compare readings from two different sources, there is always a difference. The military/govt won't allow us to get any closer to accurate than that.


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## Legbacon (Jan 20, 2004)

Hawg said:


> None of these readings are completely accurate since our GPS units (public use) do not continuously refresh. The more often a GPS unit refreshes your location as you go, the closer it is to being accurate but it will never be 100% accurate. If you compare readings from two different sources, there is always a difference. The military/govt won't allow us to get any closer to accurate than that.


They are both from the same source and the Trailforks loads my ride from Strava.


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## 411898 (Nov 5, 2008)

Travis Bickle said:


> They are both from the same source and the Trailforks loads my ride from Strava.


It has to do with the GPS device itself that was used. I've seen the exact same GPS device compared side by side on the same ride and they do not agree exactly. If GPS was that accurate, ISIS could put a missile in your coffee cup right.


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## IPunchCholla (Dec 8, 2013)

I believe strava uses not just GPS but topography to estimate elevation gain and loss. Not sure what trail forks does. It could be that trail forks is showing you the GPS elevation while strava is showing you the messaged data. No idea which is more accurate though. I always go with the lesser. 

Sent from my Nexus 5X using Tapatalk


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## Harold (Dec 23, 2003)

It doesn't matter what you do, when you move your GPS data from one source to another, elevation numbers will be different. There are a TON of reasons for this.

One is related to how each source determines moving vs. stopped time. That will always affect elevation.

Another is related to how each source actually calculates elevation gain. Strava does a PILE of extra processing and calculation to your files.

Yet another relates to the elevation source. Does your device have a barometric altimeter? How do you know if each site is actually using that sensor? With Strava, it's difficult to know, because Strava will frequently throw out data from extra sensors if there are errors in your GPS data that it has to reprocess. It makes sense why they'd do this, but it happens. If the site isn't using barometric altimeter data from your device to determine elevation, what is it using? It's using a digital elevation model that was sourced from elsewhere. What is its resolution? Strava is pretty vague about this for the data it uses, because it's not the same for everywhere. All they pretty much say is that they use higher resolution data when it's available. What does Trailforks use? Higher resolution DEM data is going to result in higher change numbers, because it will capture more small changes that would be missed with lower resolution DEM data. What's the spatial accuracy of those DEM files? Think about it, they'll never be exactly 100% the same unless the two sites use the exact same data. There's going to be some georeferencing error associated with those elevation datasets they have. And knowing what goes into creating them, I know that there isn't consistent error across the whole area of the dataset. If you rode through an area where there were steep slopes and the file was only off by a couple of feet, combined with the error from your GPS data, the resulting difference in the climbing numbers will be compounded.

I'm sure there's even more going on being the scenes on these kinds of websites. As an aside, I have done rides where the elevation change totals of my ride vary by many thousands of feet depending on where I have my data analyzed. As for me, I'm an optimist. I like whichever one reports the highest climbing total, whether it's an exaggeration or not.


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## Le Duke (Mar 23, 2009)

The other problem with using high resolution DEM files is the processing time associated with it. For every 30x30m DEM pixel, you have 9 10x10m pixels. Which means significantly more calculations, etc. That adds up when you have a large user base. 

Quicker results or more accurate results. Pick one.


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## luvdabeach2001 (Nov 11, 2011)

Same problem here.
Rode yesterday and recorded ride with Garmin 125, (auto pause disabled). The ride was auto upload to Strava and then to Trailforks.

Garmin Connect...21.63mi...2441ft
Strava................21.6 mi...2314ft
Trailforks............22....mi...3695ft

For the record I prefer the Trailforks elevation data.


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