Author Topic: Viewranger - ascent discrepancy  (Read 520 times)

AFANASIEW

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Viewranger - ascent discrepancy
« on: 09:04:09, 25/06/18 »
Between routes I've created on the Viewranger website then synced to my Android phone and the tracks recorded when I walk the routes, there's a consistent 40-65% discrepancy. The routes created on OS maps give a reading for ascent in feet, e.g. Land's End to Penzance as 2772 ft (= 852 metres) which, when walked, turn out to be 40-65% greater - 1184 metres in this example. This matters because I'm planning to do LEJOG next year, starting with the northern side of the SWCP, and do not want to underestimate the ascents in north Devon, thereby potentially scuppering the whole enterprise.


Do others experience the same thing? Is it simply down to adding more waypoints when creating the route?
It's simple - one foot in front of the other.

sussamb

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Re: Viewranger - ascent discrepancy
« Reply #1 on: 10:23:50, 25/06/18 »
No, it's more to do with the inaccuracy in GPS when calculating elevation.  There's info here on a Garmin site that applies to all GPS based elevation

https://support.garmin.com/en-GB/?faq=QPc5x3ZFUv1QyoxITW2vZ6&searchType=noProduct&utm_source=faqSearch
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AFANASIEW

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Re: Viewranger - ascent discrepancy
« Reply #2 on: 11:17:34, 25/06/18 »
No, it's more to do with the inaccuracy in GPS when calculating elevation.  There's info here on a Garmin site that applies to all GPS based elevation

https://support.garmin.com/en-GB/?faq=QPc5x3ZFUv1QyoxITW2vZ6&searchType=noProduct&utm_source=faqSearch


So which is the truer figure? The satellite error factor doesn't, presumably, apply to routes drawn on OS mapping?
It's simple - one foot in front of the other.

sussamb

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Re: Viewranger - ascent discrepancy
« Reply #3 on: 11:50:13, 25/06/18 »
The truer figure is not the one produced by your smart phone ...
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AFANASIEW

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Re: Viewranger - ascent discrepancy
« Reply #4 on: 12:15:52, 25/06/18 »
The truer figure is not the one produced by your smart phone ...
Well I guess that's a relief, although it [censored] my balloon over the apparent 6,161 feet of ascent between Ladram Bay and Lyme Regis.
It's simple - one foot in front of the other.

sussamb

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Re: Viewranger - ascent discrepancy
« Reply #5 on: 13:05:23, 25/06/18 »
If you want better elevation accuracy you need a GPS that uses barometric elevation or reads the data from a map that contains elevation data.
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BuzyG

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Re: Viewranger - ascent discrepancy
« Reply #6 on: 23:05:49, 01/07/18 »
For sure there are errors in the OS height mesh used on some sites.  I know of several specific spots where I walk regularly, that show the correct elevation on the map, but do not then calculate the evevation change correctly, Sharp tor on Bodmin, for Example always reads 20m lower than charted. when I plot a route accross it on Walking Highlands.  Generally though I find the route planners pretty accurate, as compared to counting the contour lines along the route.
« Last Edit: 23:09:07, 01/07/18 by BuzyG »

ninthace

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Re: Viewranger - ascent discrepancy
« Reply #7 on: 09:59:28, 02/07/18 »
Apart from the inaccuracies in gps based height informationa, ascent calculations for routes on the coastal path whenever the contours are close together are unreliable. A small error in plotting or recording your position combined with “noise” in the database of the mapping app you are using can put you at the bottom of the cliff when you are at the top and vice versa.  As Sussamb says, barometric altitude recording is your best option and I have found even that can be out if used over a long period. If you do use barometric data, you need to know your starting height to calibrate the altimeter.


As an aside, I have just spent 10 days walking the Alps and you would not believe the discrepancies in the ascent data according to which app you use to calculate. Dropping a trace into gpsies.com for example gives a markedly lower estimate than GoogleEarth.
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