Bug report/feature request
11
votes
Resolved: Elevation Data Accuracy
Started by
Cullen King
on
Feb 25, 10
There is alot of talk about elevation data accuracy. Many people take 'true' numbers to be those provided by Garmin, however, this isn't necessarily the best metric. For example, on an Edge 205 which uses a poor accuracy GPS elevation data, no amount of processing is going to bring that elevation data into 'perfection'. However, we do perform some pretty advanced smoothing to elevation data in order to minimize errors in gain/loss. We are continually working on improving our elevation accuracy with new math formulas. The current idea for those who are math inclined, is to use a Kalman filter to learn and smooth data using multiple signal sources. I'll continue to update this issue as we get more work done on this!
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The problems come in when you realize that a GPS unit doesn't have super accurate elevation data. Say you are riding a perfectly flat road, but your GPS unit is only accurate to 10 feet. All along the perfectly flat road, we then see gains and losses due to the GPS unit being inaccurate. This is where smoothing comes in, and is the reason why every piece of software and every site has a different value for elevation gain and loss. We are using a pretty advanced filter called a Sinc Filter, which is used in electronics for signal processing. After playing around for a solid week, I felt this was the best filtering I could do at the time. It provides results that match somewhere between what 4 separate Garmin units reports, as well as the USGS elevation data for the united states.
Anthony, we do have a correction utility if you edit your trip. You can see it in the lower right corner of the edit trip screen. This is useful for really poor elevation sets due to the GPS unit being really inaccurate (anything without a barometric pressure altimeter like the 305/605/705 have). We can reset their elevation data to the USGS provided values which are accurate to within a couple meters. However we only have this data for the united states, though we are working on expanding it to the rest of the world.
I have a friend who is a PhD student in artificial intelligence currently looking into better ways to get rid of this noise, so I hope to have even better improvements in the coming months. However with that being said, I feel we do offer the most accurate elevations of any service out there.
You said "We do have a correction utility if you edit your trip. You can see it in the lower right corner of the edit trip screen."
I choose My Profile -> Routes -> Edit and don't see the option. Can you point me in the right direction?
Thank you,
Nathan
It's a bit confusing, which is why we are working on redefining the relationship between routes/trips. We are moving towards the concept of 'activities' to replace trips, and integrating more workout specific verbiage and metrics into these activities. This should help this confusion.
Let me know if that's still confusing, or if your route is different for some reason.
Reservoirs 5
Miles Elevation % of max Source
37.1 2258 100.0% Trimble Outdoors
36.9 2247 99.5% VeloRoutes
37.2 2009 89.0% Ride with GPS
37.5 2125 94.1% Topo 5 software
36.8 2070 91.7% Bikely
37.5 1687 74.7% Garmin 76CSX
36.8 1631 72.2% GPSies
37.2 1349 59.7% Bike Route Toaster
36.5 1214 53.8% Bikemap.net
37.0 974 43.1% Map My Ride
36.9 778 34.5% Road Bike Rides
The route is 37340.
Garmin 76CSX is my gps kept in my back pocket, so it has extra inaccuries.
3/25: +410/-416 ft, max. grade 7.2%
4/01: +301/-299 ft, max. grade 5.6%
Again, these are on the same route. Why the height and grade discrepancy?
As far as correction goes, we can correct it to the USGS provided dataset values, but, my guess is the sensor data is more accurate. What I am going to experiment with eventually, is 'fusing' the two datasets together, so more consistent results are obtained. There is no perfect solution unfortunately, but, I have tuned our algorithms using two 305's, a 500 and a 705. They all reported pretty close to eachother, so my guess is that drifts from one day to the next are more a result of weather issues than anything else. It's a hard problem, and I am slowly improving our solutions, but we aren't done yet.
I have a 100 mile route that I just rode. #61731
You have it at 4284 feet climbing
Bikely at 3244
Sigma Computer 3864
havent done it on MMR.
Another ride I did recently the computer came in at 1386 and Ridew/GPS came in at 1262.
It had a ferry river crossing which could be off.
I have wondered on bridges that cross large canyons if the mapping software follows the land vs the road???