Cellular elevation gain accuracy
#1
Half way there
Thread Starter
Join Date: Sep 2015
Location: North Carolina
Posts: 2,955
Bikes: Many, and the list changes frequently
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 985 Post(s)
Liked 879 Times
in
526 Posts
Cellular elevation gain accuracy
I've been using the MapMyRide app to monitor my rides and find that its distance stats match well with my cyclometer. I've never paid much attention to the elevation stats, though. Well today I encountered something most curious that has me wondering whether they are at all accurate. I took advantage of a nice spring day today to go for a row in the new skiff . I wanted to get an idea of my distance and speed so I started the app. After a rather nice row I took a look at the stats and found that I did a total elevation gain of 152 feet with the highest elevation 60 feet above the lowest. What's the deal with this? I figure I surely would have noticed that 50 foot rise and drop in less than a mile. The lake seemed dead flat to me, but maybe I'm missing something.
#2
Newbie
MapMyRide uses your cellphone GPS for navigation.
GPS vertical position determination is less accurate than horizontal positions, so you are are going to have more error in the vertical dimension and therefore in altitude gain/loss than in position and velocity. Also, GPS measures altitude relative to a “reference ellipsoid” rather than the actual earth surface - although over a mile than won’t make much of a difference in vertical gain/loss.
GPS vertical position determination is less accurate than horizontal positions, so you are are going to have more error in the vertical dimension and therefore in altitude gain/loss than in position and velocity. Also, GPS measures altitude relative to a “reference ellipsoid” rather than the actual earth surface - although over a mile than won’t make much of a difference in vertical gain/loss.
#3
Senior Member
Join Date: Apr 2015
Location: Georgia
Posts: 654
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 236 Post(s)
Liked 196 Times
in
130 Posts
As mentioned, GPS elevation measurements tend to be less accurate - with the satellites generally overhead the Z accuracy is less than the X & Y accuracy, and thus change-in-elevation figures can be wonky. Some apps will "correct" the elevation using your position (X &Y) on the basemap. See https://support.strava.com/hc/en-us/...on-Strava-FAQs
Cycling computers these days typically have a barometric altimeter which does a far better job of measuring changes in elevation.
Cycling computers these days typically have a barometric altimeter which does a far better job of measuring changes in elevation.
#4
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,241
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4222 Post(s)
Liked 1,322 Times
in
916 Posts
After a rather nice row I took a look at the stats and found that I did a total elevation gain of 152 feet with the highest elevation 60 feet above the lowest. What's the deal with this? I figure I surely would have noticed that 50 foot rise and drop in less than a mile. The lake seemed dead flat to me, but maybe I'm missing something.
These numbers are likely close to noise. You really need steeper and longer slopes to get out of the noise.
GPS is not appropriate for elevation gain. Garmin treats barometric data as better (but even that's not perfect). Your phone might have a barometer and the gain might be using that.
People often think that elevation data is better than it is in reality. It could easily be +20% at larger numbers (even more when the ride is flat). That is, it's going to be more accurate for hillier rides. It's best to treat gain as an estimate.
Last edited by njkayaker; 04-05-22 at 08:36 AM.
#5
Senior Member
Join Date: Nov 2010
Location: Along the Rivers of Pittsburgh
Posts: 1,255
Bikes: 2011 Novara Forza Hybrid, 2005 Trek 820, 1989 Cannondale SR500 Black Lightning, 1975 Mundo Cycles Caloi Racer
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 258 Post(s)
Liked 291 Times
in
157 Posts
For a real giggle, ride through a downtown section of a city with tall buildings. I ride through downtown Pittsburgh and MapMyRide will show crazy elevation changes. Obviously I must be riding on the rooftops of the highrises!
#6
Senior Member
Join Date: Feb 2015
Location: Mission Viejo
Posts: 5,772
Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970
Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1936 Post(s)
Liked 2,150 Times
in
1,313 Posts
I’ve been using an iwatch to measure my elevation gain on rides. My wife and I will sometimes use it on short hikes.
Basically it shows elevation gain and also shows the min and max elevation. Subtracting the min from max never gives the same elevation gain, it is always greater.
I’m not certain of the algorithm used, but I always figured there has to be some real time recording and not just absolutes.
For instance if you ride on a flat stretch with 10 underpasses, or even overpasses, how are they recorded. I’ve never checked for these? Technically the elevation gain is zero for the overpass/underpass.
John
Basically it shows elevation gain and also shows the min and max elevation. Subtracting the min from max never gives the same elevation gain, it is always greater.
I’m not certain of the algorithm used, but I always figured there has to be some real time recording and not just absolutes.
For instance if you ride on a flat stretch with 10 underpasses, or even overpasses, how are they recorded. I’ve never checked for these? Technically the elevation gain is zero for the overpass/underpass.
John
#7
Sr Member on Sr bikes
I think that irregularities like this are due to glitches in the proprietary software of the fitness app. Here’s why I think that. Attached is the screenshot of the elevation profile from a run I did in 2019 along the beach at a resort in Punta Cana, D.R. And I mean I jogged right along the water’s edge so there were no hills. But, for the 4-mile jog along the water there’s a total of 1355 feet of elevation. You’ll notice that at a couple places on the profile it goes from ZERO feet elevation way down to more than negative 900 feet in the space of just a couple hundred yards. I did this particular run to see if it would mimic the same irregularity from the previous year…that unfortunately I didn’t notice until we’d returned home from the vacation. Sure enough…it made the same exact elevation plunge in the same exact place as it did the previous year. And I can assure you there wasn’t a “Grand Canyon” there on the beaches of the D.R. that I fell into. This activity was recorded with my iPhone using the Strava app. When I made this investigative run the second year, I also wore a Garmin GPS watch. When I looked at the elevation profile on the Garmin…there were no erratic elevation plunges, just normal elevation for a jog along the beach. So either there was/is some glitch in the Strava software, or software that Strava uses…or there is some sort of electromagnetic disturbance right at that particular spot that causes the cell phone’s GPS reception to go haywire. But then again it’s probably NOT that because ‘GPS reception is GPS reception’ regardless of the device. So it must be in a software algorithm.
FWIW…I have a friend currently living in the Pensacola, FL area. On one of his regular cycling routes he’s experiencing a similar occurrence. He’s riding along road adjacent to the waterfront. No bridges or overpasses. But at one point (same place every time) it shows him going up/down a hill of about 250 feet in the space of less than 100 yards.— Dan
FWIW…I have a friend currently living in the Pensacola, FL area. On one of his regular cycling routes he’s experiencing a similar occurrence. He’s riding along road adjacent to the waterfront. No bridges or overpasses. But at one point (same place every time) it shows him going up/down a hill of about 250 feet in the space of less than 100 yards.— Dan
Last edited by _ForceD_; 04-05-22 at 11:05 AM.
#8
Senior Member
Join Date: Apr 2015
Location: Georgia
Posts: 654
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 236 Post(s)
Liked 196 Times
in
130 Posts
I’ve been using an iwatch to measure my elevation gain on rides. My wife and I will sometimes use it on short hikes.
Basically it shows elevation gain and also shows the min and max elevation. Subtracting the min from max never gives the same elevation gain, it is always greater.
I’m not certain of the algorithm used, but I always figured there has to be some real time recording and not just absolutes.
For instance if you ride on a flat stretch with 10 underpasses, or even overpasses, how are they recorded. I’ve never checked for these? Technically the elevation gain is zero for the overpass/underpass.
John
Basically it shows elevation gain and also shows the min and max elevation. Subtracting the min from max never gives the same elevation gain, it is always greater.
I’m not certain of the algorithm used, but I always figured there has to be some real time recording and not just absolutes.
For instance if you ride on a flat stretch with 10 underpasses, or even overpasses, how are they recorded. I’ve never checked for these? Technically the elevation gain is zero for the overpass/underpass.
John
The elevation gain represents the sum total of how much elevation you've climbed during the ride. Without subtracting descents.
So if you ride a flat route and climb over a 50' tall bridge three times it'd report 150ft elevation gain (assuming 100% accurate readings, which doesn't occur)
#9
Senior Member
Join Date: Feb 2015
Location: Mission Viejo
Posts: 5,772
Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970
Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1936 Post(s)
Liked 2,150 Times
in
1,313 Posts
It's collecting the info in real time, though likely smoothed.
The elevation gain represents the sum total of how much elevation you've climbed during the ride. Without subtracting descents.
So if you ride a flat route and climb over a 50' tall bridge three times it'd report 150ft elevation gain (assuming 100% accurate readings, which doesn't occur)
The elevation gain represents the sum total of how much elevation you've climbed during the ride. Without subtracting descents.
So if you ride a flat route and climb over a 50' tall bridge three times it'd report 150ft elevation gain (assuming 100% accurate readings, which doesn't occur)
John
#10
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,241
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4222 Post(s)
Liked 1,322 Times
in
916 Posts
You could, for example, be up-and-down the same hill multiple times.
Barometer is the best, GPS is inaccurate (and doesn't work inside/undercover), and DEM often doesn't include the elevation of bridges or tunnels and has some other issues as well.
Your iWatch should have a barometer.
https://slate.com/technology/2015/03...r-station.html
The difference between the lowest and highest elevation just uses two points. The elevation gain is looking at the elevation of every point.
Last edited by njkayaker; 04-05-22 at 11:30 AM.
#11
Senior Member
Join Date: May 2010
Location: Bastrop Texas
Posts: 4,418
Bikes: Univega, Peu P6, Peu PR-10, Ted Williams, Peu UO-8, Peu UO-18 Mixte, Peu Dolomites
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 929 Post(s)
Liked 1,595 Times
in
1,021 Posts
Here's another one. Up in Northern Alaska the elevation points are accurate but the distances are off... Go Figure.
All in all, for a free app, Map My Ride has been great...
All in all, for a free app, Map My Ride has been great...
__________________
No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)
No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)
#12
Tragically Ignorant
Join Date: Jun 2018
Location: New England
Posts: 15,613
Bikes: Serotta Atlanta; 1994 Specialized Allez Pro; Giant OCR A1; SOMA Double Cross Disc; 2022 Allez Elite mit der SRAM
Mentioned: 62 Post(s)
Tagged: 0 Thread(s)
Quoted: 8186 Post(s)
Liked 9,094 Times
in
5,053 Posts
I've been using the MapMyRide app to monitor my rides and find that its distance stats match well with my cyclometer. I've never paid much attention to the elevation stats, though. Well today I encountered something most curious that has me wondering whether they are at all accurate. I took advantage of a nice spring day today to go for a row in the new skiff . I wanted to get an idea of my distance and speed so I started the app. After a rather nice row I took a look at the stats and found that I did a total elevation gain of 152 feet with the highest elevation 60 feet above the lowest. What's the deal with this? I figure I surely would have noticed that 50 foot rise and drop in less than a mile. The lake seemed dead flat to me, but maybe I'm missing something.
Were you row, row, rowing your boat, gently up the lake?
Likes For livedarklions:
#13
Tragically Ignorant
Join Date: Jun 2018
Location: New England
Posts: 15,613
Bikes: Serotta Atlanta; 1994 Specialized Allez Pro; Giant OCR A1; SOMA Double Cross Disc; 2022 Allez Elite mit der SRAM
Mentioned: 62 Post(s)
Tagged: 0 Thread(s)
Quoted: 8186 Post(s)
Liked 9,094 Times
in
5,053 Posts
I think that irregularities like this are due to glitches in the proprietary software of the fitness app. Here’s why I think that. Attached is the screenshot of the elevation profile from a run I did in 2019 along the beach at a resort in Punta Cana, D.R. And I mean I jogged right along the water’s edge so there were no hills. But, for the 4-mile jog along the water there’s a total of 1355 feet of elevation. You’ll notice that at a couple places on the profile it goes from ZERO feet elevation way down to more than negative 900 feet in the space of just a couple hundred yards. I did this particular run to see if it would mimic the same irregularity from the previous year…that unfortunately I didn’t notice until we’d returned home from the vacation. Sure enough…it made the same exact elevation plunge in the same exact place as it did the previous year. And I can assure you there wasn’t a “Grand Canyon” there on the beaches of the D.R. that I fell into. This activity was recorded with my iPhone using the Strava app. When I made this investigative run the second year, I also wore a Garmin GPS watch. When I looked at the elevation profile on the Garmin…there were no erratic elevation plunges, just normal elevation for a jog along the beach. So either there was/is some glitch in the Strava software, or software that Strava uses…or there is some sort of electromagnetic disturbance right at that particular spot that causes the cell phone’s GPS reception to go haywire. But then again it’s probably NOT that because ‘GPS reception is GPS reception’ regardless of the device. So it must be in a software algorithm.
FWIW…I have a friend currently living in the Pensacola, FL area. On one of his regular cycling routes he’s experiencing a similar occurrence. He’s riding along road adjacent to the waterfront. No bridges or overpasses. But at one point (same place every time) it shows him going up/down a hill of about 250 feet in the space of less than 100 yards.— Dan
FWIW…I have a friend currently living in the Pensacola, FL area. On one of his regular cycling routes he’s experiencing a similar occurrence. He’s riding along road adjacent to the waterfront. No bridges or overpasses. But at one point (same place every time) it shows him going up/down a hill of about 250 feet in the space of less than 100 yards.— Dan
It's the holes where they store the Pokemon.
#14
Senior Member
Join Date: Apr 2015
Location: Georgia
Posts: 654
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 236 Post(s)
Liked 196 Times
in
130 Posts
And to emphasize that these figures are approximate - my reported total descent was 479ft, yet I didn't end up hovering 26 ft above my parked car.
Likes For Moe Zhoost:
#16
Half way there
Thread Starter
Join Date: Sep 2015
Location: North Carolina
Posts: 2,955
Bikes: Many, and the list changes frequently
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 985 Post(s)
Liked 879 Times
in
526 Posts
Well, it turns out that it's not noise at all. I reviewed my rowing track to check where the elevation changes were occurring and discovered that the highest elevations were close to shore. Apparently the elevation data are referenced to the lake bottom, not the actual surface.
Likes For Moe Zhoost:
#17
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,241
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4222 Post(s)
Liked 1,322 Times
in
916 Posts
Well, it turns out that it's not noise at all. I reviewed my rowing track to check where the elevation changes were occurring and discovered that the highest elevations were close to shore. Apparently the elevation data are referenced to the lake bottom, not the actual surface.
The issue might have been more apparent if the complete data (horizontal location and elevation) was provided.
Likes For njkayaker:
#18
Tragically Ignorant
Join Date: Jun 2018
Location: New England
Posts: 15,613
Bikes: Serotta Atlanta; 1994 Specialized Allez Pro; Giant OCR A1; SOMA Double Cross Disc; 2022 Allez Elite mit der SRAM
Mentioned: 62 Post(s)
Tagged: 0 Thread(s)
Quoted: 8186 Post(s)
Liked 9,094 Times
in
5,053 Posts
Well, it turns out that it's not noise at all. I reviewed my rowing track to check where the elevation changes were occurring and discovered that the highest elevations were close to shore. Apparently the elevation data are referenced to the lake bottom, not the actual surface.
I was wondering about that this morning. I'd be curious to know whether the app is using the actual lake bottom numbers or just extrapolating from the elevation of the nearest shoreline.
Any chance you could get on an ocean liner anytime soon?
Likes For livedarklions:
#19
don't try this at home.
Join Date: Jan 2006
Location: N. KY
Posts: 5,918
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 964 Post(s)
Liked 496 Times
in
343 Posts
Well, it turns out that it's not noise at all. I reviewed my rowing track to check where the elevation changes were occurring and discovered that the highest elevations were close to shore. Apparently the elevation data are referenced to the lake bottom, not the actual surface.
Here's an extreme example: on my ride up to Mt Mitchell in NC, I stopped at the Craggy Gardens visitor center for about 3-4 minutes. A dark summer cloud passed by, and the wind picked up. The barometric pressure went up, making my Garmin 705 think the elevation had dropped by 350 feet. (Those Garmins are stupid. It could easily get new vertical GPS readings while I'm stopped, but it never did. It just did differentials off the initial elevation, and even that could be way off. I think the newer ones are better.)
Visitor center stop at mile 18.4:
#20
don't try this at home.
Join Date: Jan 2006
Location: N. KY
Posts: 5,918
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 964 Post(s)
Liked 496 Times
in
343 Posts
Ha, here's my post from 2015 in another elevation accuracy thread. It's a perennial subject.
Every device and site uses it's own methods to smooth out the raw data. And different devices may use GPS, barometer, or post-event map data to determine elevations.
I expect or accept maybe a 10% inaccuracy in general. That's good enough.
Every device and site uses it's own methods to smooth out the raw data. And different devices may use GPS, barometer, or post-event map data to determine elevations.
I expect or accept maybe a 10% inaccuracy in general. That's good enough.
#21
don't try this at home.
Join Date: Jan 2006
Location: N. KY
Posts: 5,918
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 964 Post(s)
Liked 496 Times
in
343 Posts
And on ridwithgps, for planning routes, sometimes a fairly recent road cut isn't known, so it shows a steep climb. Or a creek crossing bridge drops down to the creek level and back up again.
The most obvious is the tunnels on the Blue Ridge Parkway. The local elevations go up and over the ridge line, making very steep grades on the route there.
#22
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,241
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4222 Post(s)
Liked 1,322 Times
in
916 Posts
You really wouldn't want it to keep fussing with the elevation every time you stopped.
Anyway, cyclists generally are interested in elevation gain (not absolute elevation).
The drop in atmospheric pressure when you were stopped should not have effected the gain much. (It would have effected the elevation loss but riders don't tend to care much about that.)
Oh, that's likely. A post-event method, like strava has as an option, uses known elevation points. But it has to estimate the exact elevation at spots in between, and that's difficult on roads along a hill slope. Where exactly is the road surface?
And on ridwithgps, for planning routes, sometimes a fairly recent road cut isn't known, so it shows a steep climb. Or a creek crossing bridge drops down to the creek level and back up again.
The most obvious is the tunnels on the Blue Ridge Parkway. The local elevations go up and over the ridge line, making very steep grades on the route there.
And on ridwithgps, for planning routes, sometimes a fairly recent road cut isn't known, so it shows a steep climb. Or a creek crossing bridge drops down to the creek level and back up again.
The most obvious is the tunnels on the Blue Ridge Parkway. The local elevations go up and over the ridge line, making very steep grades on the route there.
This is why you want your device to measure it. For tunnels, you need a barometer (GPS doesn't work in tunnels and GPS is poor for elevation anyway).
Strava can use the elevation other people recorded for your recorded ride.
Last edited by njkayaker; 04-07-22 at 08:21 AM.
#23
Tragically Ignorant
Join Date: Jun 2018
Location: New England
Posts: 15,613
Bikes: Serotta Atlanta; 1994 Specialized Allez Pro; Giant OCR A1; SOMA Double Cross Disc; 2022 Allez Elite mit der SRAM
Mentioned: 62 Post(s)
Tagged: 0 Thread(s)
Quoted: 8186 Post(s)
Liked 9,094 Times
in
5,053 Posts
Oh, that's likely. A post-event method, like strava has as an option, uses known elevation points. But it has to estimate the exact elevation at spots in between, and that's difficult on roads along a hill slope. Where exactly is the road surface?
And on ridwithgps, for planning routes, sometimes a fairly recent road cut isn't known, so it shows a steep climb. Or a creek crossing bridge drops down to the creek level and back up again.
The most obvious is the tunnels on the Blue Ridge Parkway. The local elevations go up and over the ridge line, making very steep grades on the route there.
And on ridwithgps, for planning routes, sometimes a fairly recent road cut isn't known, so it shows a steep climb. Or a creek crossing bridge drops down to the creek level and back up again.
The most obvious is the tunnels on the Blue Ridge Parkway. The local elevations go up and over the ridge line, making very steep grades on the route there.
According to the MapMy page, they use USGS data, so who knows what that's indicating for a lake's surface?
Likes For livedarklions:
#24
Half way there
Thread Starter
Join Date: Sep 2015
Location: North Carolina
Posts: 2,955
Bikes: Many, and the list changes frequently
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 985 Post(s)
Liked 879 Times
in
526 Posts
#25
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,241
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4222 Post(s)
Liked 1,322 Times
in
916 Posts
https://support.strava.com/hc/en-us/...%20to%20Strava.
It's common in "debugging" situations that people only report the information they think is important. I like to see "everything" because what people think is important often isn't.
Your original post didn't even provide the elevation profile. My comment about noise was based on the very limited information you provided.
No one uses these to determine elevation gain on flat water. It's not too surprising that this use-case doesn't work very well.
Last edited by njkayaker; 04-07-22 at 11:51 AM.