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Who to believe? Garmin Connect or Ridewithgps?

Old 04-01-18, 05:01 PM
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GadgetGirlIL
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Who to believe? Garmin Connect or Ridewithgps?

I did a 68 mile out and back ride today. I recorded it both with my Garmin 310xt (elevation corrections are applied when it syncs to Garmin Connect) as well as exported the .GPX file from my Garmin eTrek 20 which I then imported into Ride With GPS.

Garmin Connect claims I had 1,209 feet of elevation gain. Ride With GPS claims the route had 2,519 feet of elevation gain. WTH?

While I'd like to believe Ride With GPS's value, I really believe that the Garmin Connect number is more accurate. The route has some small hills but they are nothing like those on the routes I do up in southern Wisconsin.

Any thoughts on why there is such a wide variation between the two sites?

For those in Illinois, I rode from Lisle to Oak Forest and back utilizing the bikeways (Southern DuPage Regional Trail, Woodridge Bikeways System, Veterans Memorial Trail, Centennial Trail, Cal-Sag Trail, and Tinley Creek Trail).
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Old 04-01-18, 05:30 PM
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A barometric altimeter will be much more accurate at cumulative elevation gain than relying on GPS alone. I'm not familiar with the GPS units you mention, but some Garmins do have barometric altimeters. Free web-based elevation databases can be very inaccurate when dealing with bridges, tunnels, and roads along cliffs or canyons.
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Old 04-01-18, 05:51 PM
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What do you get if you import the TCX file into RWGPS?
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Old 04-01-18, 06:21 PM
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No climbing data is CORRECT.

Barometric data is subject to the variation in the weather. When a high pressure system moves in during a ride, barometric measurement will assume you descended more than you actually did; low pressure, the barometric method assumes you climbed to higher altitudes to get those lower readings.

Non-barometric measurements rely on available elevation data for the roads ridden. Those data points can be off because the method used to get the original data may have picked up water levels instead of the roadway of the bridge; they may also have picked up the tops of trees (leaves) that hide the roadway from satellite recordings.

Further, RWGPS, etc., etc., etc., each has their own algorithm for smoothing (or eliminating) data points. RWGPS, etc., etc., etc., have each been known to change their algorithms. E.g., RWGPS originally reported about 3900 feet of climbing on my Bahama Beach perm-pop, then RWGPS reported 2200, and now (if I recall correctly) RWGPS reports about 2900 feet. Riiiight!!! Not so much.

RWGPS claims that they changed their algorithm to more closely match readings that people got from (I think it was Garmin) GPS units. Bull-oney. Everyone that has ridden the Bahama Beach standard course, and has told me their climbing result, has been between roughly 3600 and 3900 feet.

It seemed to me that RWGPS "smoothed" rolling hills / repeated creek crossing such as on Bahama Beach, but kept the totals for mountain climbs pretty much the same.

If the above is the case, then flat-lands such as you rode will likely be under-reported by RWGPS (and most, maybe all) the competing sites. I am originally from NW Illinois and lived / worked in Chicagoland for seven years after graduating from university.

Anyway, my conclusion is that NO climbing data / report is actually CORRECT.

Last edited by skiffrun; 04-01-18 at 06:25 PM.
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Old 04-01-18, 07:29 PM
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Originally Posted by johnny99 View Post
A barometric altimeter will be much more accurate at cumulative elevation gain than relying on GPS alone.
Not always. Had a barometric altimeter tell me that the elevation at the end of a loop ride was 1000' higher than the start due to a storm front moving into the area.

Cumulative elevation gain is particularly hard to determine accurately if the terrain consists of lots of fairly small ups and downs. If the measurement error on each one is 50' you can end up with a very large total error. OTOH, routes with only a few major climbs usually result in pretty consistent readings for cumulative gain.
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Old 04-01-18, 08:18 PM
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I upload my rides to RWGPS and Strava from my Garmin Edge 520, and RWGPS always overestimates elevation. Sometimes nearly twice the amount shown on Strava. Even when a storm or similar screws up with the elevation data from the Garmin, RWGPS' "corrected" elevation is still much higher than Strava's corrected elevation.
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Old 04-01-18, 08:38 PM
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Originally Posted by skiffrun View Post
It seemed to me that RWGPS "smoothed" rolling hills / repeated creek crossing such as on Bahama Beach, but kept the totals for mountain climbs pretty much the same.
Yep, and it over-estimates for a lot of routes where bridges span those gaps but the terrain data just has the valley -- I see that more than over-smoothing around me, although I only use rwgps for routes, not post-ride data analysis.

I've had the same GPS (with barometric sensor) on the same 400k route register 6000 and 8000 feet in two different year's rides. (Same bike and rider (i.e. similar pace), fairly similar weather, too.) Both numbers seem believable, although looking at a few fellow riders' logs from both years the larger end seems more common. RWGPS thinks it's 8900, which I think is overestimating it, and I was thinking that was bridge-related, but looking at the details it actually *misses* a bunch of bridge climbing where the road is just above water level on each side and goes up over a shipping channel. Eh, who knows.

(Clearly, the world was just flatter for me one year and that's why I was faster despite having trained less. Clearly.)
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Old 04-02-18, 05:10 AM
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Originally Posted by texbiker View Post
What do you get if you import the TCX file into RWGPS?
That gave me 2,365 feet in RWGPS.
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Old 04-02-18, 05:16 AM
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Originally Posted by antimonysarah View Post
(Clearly, the world was just flatter for me one year and that's why I was faster despite having trained less. Clearly.)
+1

I'm sure hoping that the world gets a bit flatter in the Shenandoah Valley of Virginia when I'm there in 3 weeks to visit my friend and to do some cycling!

Thanks, everyone, for your insights!
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Old 04-02-18, 09:14 AM
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A couple years ago I plotted a GPS track on Google Earth so I could see what it looked like. And part of the track was along a horizontal (flat) road at the base of a cliff. But Google earth gave me some really absurd high elevation gain and loss results. It was not until I looked at the profile plot that I saw what was happening. Google Earth thought that a small part of the GPS track suddenly went straight up to the top of the cliff, then followed the cliff edge for a while, then dropped straight down again and followed the road.

So, if your estimate is based on a computer using a topographic map to get elevations, if you are in an area where there are steep hills next to the road, you can expect some error.

GPS units make estimates on location, they can be tens of feet off. I leave WAAS correction turned off on my GPS units to reduce battery consumption, that probably increases teh size of my errors by a factor of two or three. I accept that error, I really do not care if my GPS is off by 30 or 40 feet for any specific position if it will extend by battery life.

Surveyors use GPS units that are accurate to less than a tenth of a foot, but those kinds of accuracies are not found on our bikes.

In general terms the vertical error in a GPS is about twice as much as the horizontal error. Thus, after a several hour long ride your GPS can have a lot of fluctuation over time.

I am getting ready for a trip (I leave on Thursday) where part of the ride has a lot of hill climbing. A week ago I did an exercise ride on a loop near home that has a steep hill that is about 95 feet of elevation gain. I rode that loop eight times over less than one hour of time and when I looked at the elevation plot later, the height of the hill varied by about plus or minus 15 feet each of eight times that I rode it.

Bottom line is that I never trust GPS obtained elevation gain and loss data very much when it is taken over a multi-hour ride.
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Old 04-11-18, 07:59 AM
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I know that Garmin elevation corrector doesn't account for overpasses and small hills. I feel like my edge with the elevation correction turned off on the connect page is more accurate.
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