Elevation gain
#26
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,272
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4257 Post(s)
Liked 1,354 Times
in
940 Posts
Pilots of aircraft also depend on getting the altimeter setting, which is a correction factor to allow their barometric instruments to show them an accurate altitude or clearance to tercrain. Each air traffic controller will routinely give the altimeter setting for that area so the pilots know what to set on their altimeters.
There are various methods for GPS devices with a barometric sensor use to calibrate their reading to the actual elevation, but that initially takes effort from the user and only works for predetermined locations. And the GPS device AFAIK only calibrates itself at the beginning of a ride. So normal changes in barometric pressure will produce errors in what is actually done.
Almost any ride I do, the elevation I left my house at is not the shown elevation when I return.
There are various methods for GPS devices with a barometric sensor use to calibrate their reading to the actual elevation, but that initially takes effort from the user and only works for predetermined locations. And the GPS device AFAIK only calibrates itself at the beginning of a ride. So normal changes in barometric pressure will produce errors in what is actually done.
Almost any ride I do, the elevation I left my house at is not the shown elevation when I return.
How different is the elevation at the start and the end?
Drift in the reading (if it's slow) probably won't change the gain by much.
Small gains over large distances likely have a higher percentage of noise.
Last edited by njkayaker; 07-25-21 at 10:47 PM.
#27
climber has-been
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,106
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3427 Post(s)
Liked 3,564 Times
in
1,790 Posts
Having an accurate elevation is useful in one situation: when you know the elevation of the summit of your climb, and you want to know how much more climbing you have remaining.
#28
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,272
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4257 Post(s)
Liked 1,354 Times
in
940 Posts
You can also get that information from the relative elevation in the track file (if you are using one), which is how Garmin's "climbpro" works.
Accurate gain doesn't require accurate altitude. If the altitude is off by a constant amount over the course of a ride, the gain will still be the same.
Last edited by njkayaker; 07-25-21 at 11:18 PM.
#29
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,272
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4257 Post(s)
Liked 1,354 Times
in
940 Posts
From Sunnto
A Google search of accuracy of the two measurements give a raw error of 10m to 20 m for GPS (35 to 70 feet) while barometers are accurate to ±15 meters. The error is almost the same per measurement. GPS may suffer more from a refresh rate that a barometer doesn’t experience. GPS is averaged over several seconds while barometric pressure may be closer to instantaneous as it is an on-board instrument. If you are stationary, this may no make much difference but when mobile, that averaging can lead to larger errors. Most phones have both GPS and a barometer to increase accuracy.
A Google search of accuracy of the two measurements give a raw error of 10m to 20 m for GPS (35 to 70 feet) while barometers are accurate to ±15 meters. The error is almost the same per measurement. GPS may suffer more from a refresh rate that a barometer doesn’t experience. GPS is averaged over several seconds while barometric pressure may be closer to instantaneous as it is an on-board instrument. If you are stationary, this may no make much difference but when mobile, that averaging can lead to larger errors. Most phones have both GPS and a barometer to increase accuracy.
Altitude Accuracy
#31
Me duelen las nalgas
Join Date: Aug 2015
Location: Texas
Posts: 13,513
Bikes: Centurion Ironman, Trek 5900, Univega Via Carisma, Globe Carmel
Mentioned: 199 Post(s)
Tagged: 0 Thread(s)
Quoted: 4559 Post(s)
Liked 2,802 Times
in
1,800 Posts
Strava and some other activity apps reference existing databases for elevation, based on map data and data submitted by users who post data based on their computers and phones. Presumably these are reasonably accurate. At least it offers a fairly consistent baseline.
My XOSS G+ bike computer has a barometric pressure sensor and the elevation estimates vary wildly depending on the weather. I never even look at it during rides.
And because my computer elevation data is unreliable, after syncing my ride to Strava, I then use Strava's options to correct elevation and distance. This at least makes the other data relevant in comparisons with rides on the same routes.
My XOSS G+ bike computer has a barometric pressure sensor and the elevation estimates vary wildly depending on the weather. I never even look at it during rides.
And because my computer elevation data is unreliable, after syncing my ride to Strava, I then use Strava's options to correct elevation and distance. This at least makes the other data relevant in comparisons with rides on the same routes.
Likes For canklecat:
#32
Perceptual Dullard
Join Date: Sep 2009
Posts: 2,417
Mentioned: 36 Post(s)
Tagged: 0 Thread(s)
Quoted: 918 Post(s)
Liked 1,152 Times
in
491 Posts
Unless it's hella windy, an accurate power meter, an accurate speedometer, and a pretty good bathroom scale work very well for calculating altitude gained.
#33
Enthusiastic Sufferer
Join Date: Nov 2017
Location: Perth, Australia
Posts: 229
Bikes: 2015 Specialized Roubaix, 2014 Salsa Fargo, 2013 Trek Remedy, 2014 Cannondale Synapse
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 124 Post(s)
Liked 311 Times
in
107 Posts
^^^This. I and many of my riding friends use Wahoo to record and our elevations can vary by hundreds of feet on a ride. The Strava elevation correction reduces the variance substantially. It doesn't matter to me which is correct as long as I have consistency. To further muddy the water, we use RWGPS to plan routes. We rarely end up with the predicted elevation. Sometimes more, sometimes less. I can't see how a few hundred feet would matter either way.
Those extra 700m are way harder when you don't know they're coming
Likes For SapInMyBlood:
#34
Senior Member
Join Date: May 2021
Posts: 8,425
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 4403 Post(s)
Liked 4,854 Times
in
3,003 Posts
The correction feature is disabled by default for devices that use a barometer. It's enabled for devices that only use GPS.
Garmin rates barometric data as better than GPS for elevation.
The manual calibration is useful for determining altitude (which few cyclists care about). It should not matter for elevation gain.
Garmin rates barometric data as better than GPS for elevation.
The manual calibration is useful for determining altitude (which few cyclists care about). It should not matter for elevation gain.
#35
Senior Member
Join Date: May 2021
Posts: 8,425
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 4403 Post(s)
Liked 4,854 Times
in
3,003 Posts
Sure. But that's not a common interest. (I didn't say it wasn't ever useful.) It also wouldn't let you know how much more if there were inflection points.
You can also get that information from the relative elevation in the track file (if you are using one), which is how Garmin's "climbpro" works.
Accurate gain doesn't require accurate altitude. If the altitude is off by a constant amount over the course of a ride, the gain will still be the same.
You can also get that information from the relative elevation in the track file (if you are using one), which is how Garmin's "climbpro" works.
Accurate gain doesn't require accurate altitude. If the altitude is off by a constant amount over the course of a ride, the gain will still be the same.
#36
I'm good to go!
Join Date: Jul 2017
Location: Mississippi
Posts: 14,986
Bikes: Tarmac Disc Comp Di2 - 2020
Mentioned: 51 Post(s)
Tagged: 0 Thread(s)
Quoted: 6193 Post(s)
Liked 4,809 Times
in
3,317 Posts
The calibration is necessary for determining altitude. But cyclists don't care too often about that.
How different is the elevation at the start and the end?
Drift in the reading (if it's slow) probably won't change the gain by much.
Small gains over large distances likely have a higher percentage of noise.
How different is the elevation at the start and the end?
Drift in the reading (if it's slow) probably won't change the gain by much.
Small gains over large distances likely have a higher percentage of noise.
I agree the calibration is only needed for those that want to know their elevation. I've never understood the need to know actual elevation for cycling. My house is the normal start point for my rides so I have the driveway as a calibration waypoint. On the topo maps of my area a contour line goes right through it. But even that might be incorrect as the topo maps data set includes data from times before this house or even the subdivision was built. So who knows and why should I really care? I don't!
I'm not suggesting this is the reason for the OP. But this and other things can add up to always make the relative or actual elevation numbers be different from one ride to the next.
There is even an overpass I travel routinely and on days with the wind blowing steady from the soutwest, I'll show a higher elevation going over it than days with no wind. I wonder if that is a localized reduction in air pressure because the wind is being funneled along that area at a higher velocity than air elsewhere. So Bernoulli's Principle might be another reason for errors in elevation or gain/loss calcs. And it can occur in many places.
For me, elevation gain/loss is a lot like Calories. The actual exact number is not important. If someone wants to ride hilly terrain, then ride the routes that show the most gain loss per distance. Doesn't matter if they don't match up from day to day.
Map data isn't correct for total elevation gain, nor are our barometric sensors in our devices and certainly GPS calculate altitude is less trustworthy. So people need to learn to judge by the trends and not the actual exact number they will never have.
#37
climber has-been
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,106
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3427 Post(s)
Liked 3,564 Times
in
1,790 Posts
Like this Strava segment, based on some very noisy user-uploaded data.
The actual grade is about 7%, but Strava says it's 12.3%. Strava says the KOM rider climbed it with a VAM of 2703 meters per hour, which is ridiculous.
Bad Strava segment
Here's what that segment would look like with "good" GPS data:
"good" Strava segment
#38
climber has-been
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,106
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3427 Post(s)
Liked 3,564 Times
in
1,790 Posts
There is even an overpass I travel routinely and on days with the wind blowing steady from the soutwest, I'll show a higher elevation going over it than days with no wind. I wonder if that is a localized reduction in air pressure because the wind is being funneled along that area at a higher velocity than air elsewhere. So Bernoulli's Principle might be another reason for errors in elevation or gain/loss calcs.
I've noticed this on climbs with lots of switchbacks. When I'm climbing a portion with a tailwind, the climbing rate number is steady. But when I round a hairpin and turn into the wind, I'll briefly see a burst of increased climbing rate.
Alas, it's only a brief and false moment of glory.
#39
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,272
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4257 Post(s)
Liked 1,354 Times
in
940 Posts
The weather here has been pretty stable. No fronts of areas of high and low pressure moving through. Just sometimes rain and a thunderstorm that develop and dissipate in pretty much the same general area. So my last 5 rides over 2 hours had a start finish difference averaging 48 feet. The biggest 62 feet and the smallest 38 feet. Not a lot. However some where back in my history I've seen on the order of 100 feet of change or more during a ride.
There also isn't a "right" elevation gain number. It has to smooth the data (otherwise, it would count every little jiggle).
Since elevation gain is not considering grade at all, it's a weak indicator of effort anyway.
For me, elevation gain/loss is a lot like Calories. The actual exact number is not important. If someone wants to ride hilly terrain, then ride the routes that show the most gain loss per distance. Doesn't matter if they don't match up from day to day.
Map data isn't correct for total elevation gain, nor are our barometric sensors in our devices and certainly GPS calculate altitude is less trustworthy. So people need to learn to judge by the trends and not the actual exact number they will never have.
Map data isn't correct for total elevation gain, nor are our barometric sensors in our devices and certainly GPS calculate altitude is less trustworthy. So people need to learn to judge by the trends and not the actual exact number they will never have.
Last edited by njkayaker; 07-26-21 at 09:12 AM.
#41
Senior Member
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,272
Mentioned: 31 Post(s)
Tagged: 0 Thread(s)
Quoted: 4257 Post(s)
Liked 1,354 Times
in
940 Posts
How long is a coastline?
There isn't one standard for smoothing the data and what changes to include or drop.
I had a Bontrager computer that was kinda close to my Edge 800.
Which ones and how? Is it any of the common ones?
One might be able to take the gain and divide it by distance. But that wouldn't be gain (it would be a gain rate or ratio). Or, I suppose, one could ignore gain below some sort of grade threshold.
There isn't one standard for smoothing the data and what changes to include or drop.
I had a Bontrager computer that was kinda close to my Edge 800.
Which ones and how? Is it any of the common ones?
One might be able to take the gain and divide it by distance. But that wouldn't be gain (it would be a gain rate or ratio). Or, I suppose, one could ignore gain below some sort of grade threshold.
Last edited by njkayaker; 07-26-21 at 11:08 AM.
#42
Klaatu..Verata..Necktie?
Join Date: May 2007
Location: SF Bay Area
Posts: 17,961
Bikes: Litespeed Ultimate, Ultegra; Canyon Endurace, 105; Battaglin MAX, Chorus; Bianchi 928 Veloce; Ritchey Road Logic, Dura Ace; Cannondale R500 RX100; Schwinn Circuit, Sante; Lotus Supreme, Dura Ace
Mentioned: 41 Post(s)
Tagged: 0 Thread(s)
Quoted: 10424 Post(s)
Liked 11,898 Times
in
6,094 Posts
This is my observation when using Garmin's elevation correction for mountainous switchback rides. On each turn the GPS drops me off the cliff and then climbs me back up adding 1000s of feet to the ride. It makes me look good but i switch this feature off. Regrettably it seems permanently activated when using the Connect route planning function, so I defer to RWGPS when planning a ride.
Luckily, the fall didn't kill me.
__________________
"Don't take life so serious-it ain't nohow permanent."
"Everybody's gotta be somewhere." - Eccles
"Don't take life so serious-it ain't nohow permanent."
"Everybody's gotta be somewhere." - Eccles
Likes For genejockey:
#43
Klaatu..Verata..Necktie?
Join Date: May 2007
Location: SF Bay Area
Posts: 17,961
Bikes: Litespeed Ultimate, Ultegra; Canyon Endurace, 105; Battaglin MAX, Chorus; Bianchi 928 Veloce; Ritchey Road Logic, Dura Ace; Cannondale R500 RX100; Schwinn Circuit, Sante; Lotus Supreme, Dura Ace
Mentioned: 41 Post(s)
Tagged: 0 Thread(s)
Quoted: 10424 Post(s)
Liked 11,898 Times
in
6,094 Posts
I tried "starring" OLH so that I could track my progress relative to my previous best time. TWICE I started up the climb and less than half a mile into it my Garmin said I was "off segment" and stopped giving me those data. Similarly, one time when I rode up Kings Mountain,. between Garmin and Strava, I was off the road most of the time, so it didn't find segments for half the climb - so, also not for the whole climb.
__________________
"Don't take life so serious-it ain't nohow permanent."
"Everybody's gotta be somewhere." - Eccles
"Don't take life so serious-it ain't nohow permanent."
"Everybody's gotta be somewhere." - Eccles
#44
Senior Member
Join Date: Jul 2009
Posts: 5,949
Bikes: Colnago, Van Dessel, Factor, Cervelo, Ritchey
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 3949 Post(s)
Liked 7,296 Times
in
2,946 Posts
Sounds like a good place for an "Everesting" record attempt.
Likes For tomato coupe:
#45
Senior Member
Join Date: Jul 2015
Location: reno, nv
Posts: 2,299
Bikes: yes, i have one
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 1137 Post(s)
Liked 1,182 Times
in
687 Posts
i'll bet the power pod could accurately measure elevation if it only knew what your elevation was when you started.
my understanding is that it uses both grade and speed to help compute power. speed and grade are all that are needed to calculate elevation gain.
https://velocomp.com/powerpod-lite/
my understanding is that it uses both grade and speed to help compute power. speed and grade are all that are needed to calculate elevation gain.
https://velocomp.com/powerpod-lite/
#46
climber has-been
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,106
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3427 Post(s)
Liked 3,564 Times
in
1,790 Posts
Likes For terrymorse:
#47
Perceptual Dullard
Join Date: Sep 2009
Posts: 2,417
Mentioned: 36 Post(s)
Tagged: 0 Thread(s)
Quoted: 918 Post(s)
Liked 1,152 Times
in
491 Posts
You're mixing up a distance with the measurement of that distance (or, in this case, a height with the measurement of that height). This isn't a fractal problem. Distances and heights are actual things, so there is a "right" height. The measurement of that height can and does have an error, but your claim was "There also isn't a 'right' elevation gain number." There is a right elevation gain number.
Some estimates of elevation gain take grade into account.
Which ones and how? Is it any of the common ones?
Not one of the common ones, but it's one that is built on the effort it takes to climb a hill. It uses power and speed data (among other things) to build up road gradient and then integrates gradient to get elevation gain. It can reliably and repeatably reproduce small changes in road grade. Better still, we can use the Central Limit Theorem to reduce error in the elevation gained when integrating the gradient.
Originally Posted by njkayaker
Originally Posted by RChung
Originally Posted by njkayaker
Since elevation gain is not considering grade at all, it's a weak indicator of effort anyway.
Likes For RChung:
#49
Senior Member
Join Date: Dec 2010
Location: northern Deep South
Posts: 8,903
Bikes: Fuji Touring, Novara Randonee
Mentioned: 36 Post(s)
Tagged: 0 Thread(s)
Quoted: 2604 Post(s)
Liked 1,931 Times
in
1,212 Posts
Will there be a refresher tutoring session for those of us who haven't used calculus in a few decades? Or do we need to process a withdrawal from BF?
Likes For pdlamb:
#50
climber has-been
Join Date: Dec 2004
Location: Palo Alto, CA
Posts: 7,106
Bikes: Scott Addict R1, Felt Z1
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 3427 Post(s)
Liked 3,564 Times
in
1,790 Posts
You're mixing up a distance with the measurement of that distance (or, in this case, a height with the measurement of that height). This isn't a fractal problem. Distances and heights are actual things, so there is a "right" height. The measurement of that height can and does have an error, but your claim was "There also isn't a 'right' elevation gain number." There is a right elevation gain number.
How do you define the "right" length of a coastline?
Likes For terrymorse: