How much ascent on a route?

[anweledig]

Hi - I completed the Discovering Shropshire audax last weekend, a brilliant ride which was a real credit to the organisers. I did make a slight navigation error because of over-reliance on the Garmin but this was soon corrected and I got back on track.

Once I got home I uploaded the track from the Garmin and was surprised to see that it thought I had completed 6882' of ascent (I must have done more climbing than I thought ), just to check I uploaded the gpx file to a few other sites just to see the ascent and have listed the results below:

bikeroutetoaster.com 4279'
mapmyride.com 3002'
gpsies.com 5223'
aukweb (published route) 5413' (I know I climbed an extra 200' off route but this was my error)
bikely.com off-line
Garmin (605) 6882'

This leaves me a bit baffled, how much ascent was there on my route? Why is there so much variation (the actual distance variation is quite small between sites, under .25 of a mile)

Can anyone shed any light on this - and tell me which numbers I should believe?


note - just uploaded the route to garmin connect and that says I climbed 4630' - aaarggh!!

cheers

 

[the snail]

I think your garmin is probably the most accurate, because it measures what you actually do on the bike, whereas the other figures are based on counting when you cross contour lines on a map. otoh counting contour lines maybe gives a better idea of how hard the ride is - lots of small undulations add up, but aren't the same as gaining the height in one go.

 

[HLaB]

Has the 605 got a barometric altimeter if so it will be the most accurate but uploading it to Garmin Connect seems to sort out any over-readings due to interference, etc.

Edit: you did upload and yes it did sort it.

 

[albion]

From above I can see the problem with these things.Suppose you climb a mountain pass. 10' on one side of the road there could be a descent of 1000' and t'other side there could be an ascent of 1000'

 

[ColinJ]

From above I can see the problem with these things.Suppose you climb a mountain pass. 10' on one side of the road there could be a descent of 1000' and t'other side there could be an ascent of 1000'

I did a forum ride today and had plotted my route as accurately as I could from my OS mapping. My GPS was working to 7-10 metre accuracy but in one place the GPS showed me being 40 metres away from where the OS showed the road to be. If you read some of the notes about OS mapping, you will see that sometimes important features are enlarged or moved relative to others to make the maps clearer. An error of that size could easily put you half way up a hillside.

I have a good local example ... If I do a plot along the A646 from Hebden Bridge to Mytholmroyd past the site of the former Walkley's Clogs mill, the profile shows a 27 metre climb. In fact, the road goes slightly downhill! That's because the valley side is nearby and quite steep and the A646 isn't shown in its true position. Errors like that soon add up on a long route.

 

[400bhp]

There is an option on garmin website for "elevation corrections". I would have thought this is the most accurate.

My Garmin generally overreads, and by quite a bit too.

Is your 6882ft a "Garmin Corrected" elevation

 

[Fiona N]

From time to time I record a marker on the Polar (barometric altimeter) when I cycle past an OS spot height (obviously, I've looked these up previously, spot heights not having physical markers on the ground like trig points). I always reset the altimeter before I leave home and on a short ride in stable weather, the Polar is within a couple of metres which is pretty good. On longer rides and obviously unstable weather, the barometric pressure drift means that I can be 50 or 60m out at individual points so this potentially subtracts or adds a whole lot to the ride total altitude gain. Usually the pressure is falling as I'm more likely to go out in fine weather which becomes rainy than the reverse, so the recorded altitudes are mostly too high - this affects both crests and dips but always seems to work out as too much height gain rather than too little.

I would have expected GPS to be more accurate if they're not barometric - but if they're 'detected' (position) to get height, then I suppose it depends how often the sample is taken. Like someone wrote, if you're passing over a summit and the sample isn't taken at that point, then the extent of the climb is apparently reduced.

 

[PK99]

Hi - I completed the Discovering Shropshire audax last weekend, a brilliant ride which was a real credit to the organisers. I did make a slight navigation error because of over-reliance on the Garmin but this was soon corrected and I got back on track.

Once I got home I uploaded the track from the Garmin and was surprised to see that it thought I had completed 6882' of ascent (I must have done more climbing than I thought ), just to check I uploaded the gpx file to a few other sites just to see the ascent and have listed the results below:

The garmin works on barometric pressure - ie it does not measure altitude.

a regular run for me is home to richmond park, 3 times round and back.

On loading the outing into Garmin connect it invariably shows the hills in the park to be different heights on each circuit and home to be 100ft or more higher on my return than when i set off!

Enabling "Elevation corrections" in garmin connect sets things right

eg my ride today out to Edenbridge shows: 2612ft measured, 2352 corrected.

ie the reading on your Garmin is a very rough guess

I generally find the discepancy worst on whole day rides ie out in the morning chill, ride through the heat of the day, back in the evening chill seems to play havoc with the Garmin internal measurement



from garmin connect:
What are Elevation Corrections?What are Elevation Corrections?Elevation Corrections cross reference the horizontal position (latitude/longitude) provided by the GPS with elevation data that has been acquired by professional surveys. When corrections toElevation Corrections cross reference the horizontal position (latitude/longitude) provided by the GPS with elevation data that has been acquired by professional surveys. When corrections to elevation data are made, each trackpoint of your activity now contains the elevation from the web service, not the elevation provided by your GPS device.Garmin Connect selectively applies corrections to depict a more realistic representation of your elevation experience. Activities recorded from devices without a barometric altimeter are enabled with Elevation Corrections by default. Alternatively, activities recorded by devices with a barometric altimeter generally contain accurate elevation data and therefore Elevation Corrections are disabled by default. For those users who are familiar with the MotionBased Gravity service, this is the same service. elevation data are made, each trackpoint of your activity now contains the elevation from the web service, not the elevation provided by your GPS device.Garmin Connect selectively applies corrections to depict a more realistic representation of your elevation experience. Activities recorded from devices without a barometric altimeter are enabled with Elevation Corrections by default. Alternatively, activities recorded by devices with a barometric altimeter generally contain accurate elevation data and therefore Elevation Corrections are disabled by default. For those users who are familiar with the MotionBased Gravity service, this is the same service.

 

[HLaB]

Barometric is supposed to be more accurate for some reason. I quite like my old gps before it packed up, it had a Barometric gauge you could calibrate and I think it also look at the less accurate GPS data to reduce the possibility of wild readings. But as said inclement weather over longer rides makes the Barometric guage really unstable; a few years back with my latest gps (non-calibratable), I did the Ken Laidlaw Border Sportif, advertised as over 1000m of climbing in 105 miles, when I got back soaked I was a little disappointed to see my climbing in TC was only 3900ft a few months later Garmin Connect was launched and the updated ride is nearly 8500ft, I know what I want to believe .

 

[anweledig]

Thanks for all the comments and suggestions. Ie does give me a fair bit to consider. The 605 doesn't have a barometer afaik which may explain some inaccuracy and at several times on the route I was on the side of a hill with slopes above and below me. It seems the garmin connect height is possibly one of the most accurate I am going to be able to get (and more in line with my expectations). It still seems odd that the other mapping sites all give different results from the same gpx file though- presumably they have different base maps.

At least they agree on the linear distance (can 't pretend I did an extra few hundred miles )

 

[albion]

I've no idea if any systems 'lock onto the nearest logical road' with known heights.This would be fine if there was also an off-road setting.

 

[Garz]

Set your unit to a fixed value for known GPS locations. My abode is ~ 300ft above sea level and before setting this it made the ride ascent figures vary a wee bit. Reports are more stable now and I don't return home to the same point to see im lower/higher.

 

[HLaB]

Set your unit to a fixed value for known GPS locations. My abode is ~ 300ft above sea level and before setting this it made the ride ascent figures vary a wee bit. Reports are more stable now and I don't return home to the same point to see im lower/higher.

The geko 301 had that feature and I found it quite good, I don't think you can do it with the Edge

 

[Garz]

The geko 301 had that feature and I found it quite good, I don't think you can do it with the Edge

Pg 46 of the user manual.

"Setting Elevation Points"

 

[HLaB]

Pg 46 of the user manual.

"Setting Elevation Points"

Page 46 of my manual just generalises on 'History' I'll keep on looking though (perhaps they've added the feature after my Edge 305 came out). Is there a more detailed manual than the 93page Owners Manual that came with the Edge 305?