Author Topic: WOW 304,894m ascent in one afternoon. What a climb.  (Read 846 times)

wobblyknees

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I went for a short walk yesterday afternoon mostly through forest tracks with some open areas. My Garmin Etrex 20 showed I had climbed 304,894 m. All the rest of the data such as horizontal distance, time taken, seemed normal.
There is a communications mast with a plethora of dishes, antennae, etc on top of the hill I was climbing. Snow started falling about half way up and continued to end of walk. It got quite heavy towards the end.
Which is more likely to have caused the false reading -the snow or the mast?
« Last Edit: 09:46:35, 12/02/18 by wobblyknees »

April

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #1 on: 12:42:26, 12/02/18 »
I had the same problem on Saturday using a tablet/viewranger. Not as much height gain as you though  ;D

368m height gain on the Thirlmere western shore road from the dam road end to Steel End? We did visit the bothy below Fisher Crag and that is a little bit of ascent to get there. Like you the mileage seemed accurate. There was so no snow falling but the area does have a few trees about.
"Who would've thought...... you are light and darkness coming through" words by Tim Armstrong

fernman

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #2 on: 13:45:48, 12/02/18 »
I'd have thought if the cause was snow falling the problem would have been encountered 100s of times over the years by walkers and climbers, and therefore widely known.

On the other hand, I know from experience that snow affects the satellite signal to my Sky dish (satellite signal, geddit?), last night being a good example when it failed to record a programme starting at 8 p.m at which time there was a heavy snow shower.

jimbob

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #3 on: 16:23:42, 12/02/18 »
Strange, worthwhile pointing this out to the Viewranger/Garmin people. The programs work on receiving fixes from a GPS satellite and them converting those fixes wrt data from the mapping. I.e. a computer calculation of distance.  I would have thought ascent/descent calculated in the same way. It looks like maybe  the software is particularly unsafe in bad weather conditions, to the point of dangerous in fact. :-[

Sussamb usually makes worthwhile comments on these GPS matters as he seems to be the forum guru, either that or he has actually read the complete handbook and has a great memory O0
Too little, too late, too bad......

Mel

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #4 on: 18:28:48, 12/02/18 »
Hey wobblyknees, you should sign up for Trail magazine's "climb the height of Everest in a year" challenge.  I think you may have nailed it  ;D

No expense spared in pursuit of a bargain ;)
https://snailspacewalks.blogspot.co.uk/

wobblyknees

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #5 on: 20:11:12, 12/02/18 »
Unless my Etrex 20 is totally unreliable, I think I've already nailed it. I clocked up more than the climb from sea level to top of Mount Everest  in 14 days on my C2C walk.

wobblyknees

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #6 on: 10:26:27, 13/02/18 »
I transferred the track to Basecamp. Basecamp shows total ascent = 195m and total descent =186m, which looks about right.
I think this is because Basecamp calculates ascent and descent from the contours crossed on the map, whereas the GPS unit takes it's data from the satellites.


Would still welcome some advice on whether the snow or the mast caused the false reading.

April

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #7 on: 12:40:01, 13/02/18 »
Would still welcome some advice on whether the snow or the mast caused the false reading.

I would like to know this too, I estimated the ascent we did was no more than 100m yet viewranger said it was almost 4 times as much? It would be interesting to know why it was so much out.
"Who would've thought...... you are light and darkness coming through" words by Tim Armstrong

jimbob

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #8 on: 15:18:22, 13/02/18 »
Woblyknees I thought that Garmin and Viewranger both did their ascent/descent calculations in the same way as you describe base camp.

They hold all the data on contours digitally and are supposed to calculate the number "crossed" by using your actual position. In short, doing digitally what  you did manually in base camp.

It seems that without an expert view from either Garmin or Viewranger  we are all in the dark as to what happened and as I said previously this could be quite dangerous in certain situations due to our ever increasing reliance on electronics

I have submitted an enquiry to Viewranger. We'll see what they say.
« Last Edit: 15:43:24, 13/02/18 by jimbob »
Too little, too late, too bad......

jimbob

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #9 on: 16:47:53, 13/02/18 »
Well an extremely fast response from Viewranger. I did point them to the topic within the forum so they could read the whole set of issues. (Hence their mention of Garmin)
"Hi Jim,Thank you for your email.  Ascent is a tricky area for apps, though I see that huge gain was a Garmin running its own software rather than an app.  We do see more GPS issues this time of year, which I think is as much to do with extra wet layers and protection as the weather.  But signal reflections can give some spurious GPS positions too.Here's quite a detailed explanation of what we do, and why it can be wrong.  ViewRanger works out the altitude gain and loss of a track or route by calculating the altitude at every point along the track and summing the differences. If the points are a fair way apart it will also take readings along the straight lines between the two points.
So one reason for a higher than expected reading is that it has taken into account all the ups and downs of the track, at a detailed level. Often the overall gain and loss is higher than you would expect if you take these into account.
But there are times when it will over read:
If the GPS accuracy is not as good as it could be, especially on steep ground, it can over read as some points will be too high or too low. For example if you were walking along a cliff top, as an extreme example to explain this, one mis-reading off the cliff top could add hundreds of metres unwanted gain and loss as the track appears to descend and re-ascend. (And in relaity there will be several readings off, not just an odd one, so it will look like you desceneded, walked a short way, then ascended.) I appreciate you did not walk along a cliff, but this is just to explain the effect that can occur on all steep ground.
Also if the track points are spaced out, and you didn't actually move in a straight line between the points, then the extra readings it takes between points can be wrong. For example, if the cliff edge is curved.
We have a project underway to better detect unwanted deviations and reduce the two effects I have described above.
 
Regards,
 Mike"

Makes sense to me.  Thank you Viewranger Support.
Too little, too late, too bad......

April

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #10 on: 19:36:50, 13/02/18 »
Thanks jimbob, fast response from viewranger like you say  O0

There are a few "drops" going over the dam road and along the shore road at times. Apart from the ascent to the bothy there seemed to be almost no ascent or descent on the shore road. I'm going to check the ascent/descent I record on viewranger more carefully to see how accurate it really is in future.

"Who would've thought...... you are light and darkness coming through" words by Tim Armstrong

wobblyknees

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #11 on: 21:22:06, 13/02/18 »
Thanks also jimbob and thanks Viewranger support for the very succinct explanation. It makes sense to me though I must admit I don't fully understand how GPS units / apps work. I must do a bit of reading up on them. I always knew they are unreliable at calculating altitude but 304,894m as against 195m? Something is wrong. I wish Viewranger had commented on whether those microwave / communication signals near masts can interfere with GPS signals.


Also, I think Basecamp calculates altitude in the way I said. I'm using a Talkytoaster map of British Isles. If I used a different map with contour data more or less tightly packed, would I get a different total ascent result?

jimbob

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #12 on: 22:32:32, 13/02/18 »
We'll need to see if we can get an answer from Garmin now.
Too little, too late, too bad......

Addingham

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #13 on: 05:49:26, 14/02/18 »
We'll need to see if we can get an answer from Garmin now.


I hope that  was tongue in cheek. ;)  No chance. ;D

jimbob

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Re: WOW 304,894m ascent in one afternoon. What a climb.
« Reply #14 on: 12:15:33, 14/02/18 »
An IT friend has sent this to me which came froma cycling forum originally.

"In order to compute total gain, the Garmin must take point elevations often.  Each one of those has some error in it.  At first thought, you'd think those errors cancel each other out.  But the math doesn't work that way.   
 
 Assume you're riding a perfectly flat road at 500' elevation for one mile at 20 mph.  If the Garmin is taking point elevations every 30 seconds, it will take six elevations.  (It actually takes them far more often).  The Garmin will compute elevations (each probably with a little error) of say: 510, 505, 495, 500, 505, 500 which show gains of:
 
 495->500 = +5'
 500->505 = +5'   
 Total Gain = +10'
 
 So the Garmin computed +10' of climbing when there should have been 0' of climbing.  Over a long ride, this error adds up big.

One issue that confuses many people is that they assume that because the Garmin's total ascent and total descent are relatively close that the device is accurate.  But again, the math doesn't work that way.  Take the same series of six elevations above.  The total descent is:
 
 510->505 = -5'
 505->495 = -10'
 505->500 = -5'
 Total Descent = -20'
 
 It appears that +10 and -20 are pretty close so the device must be correct.  WRONG.  The false descent is based on the same incorrect elevation series and therefore Ascent and Descent will always be similar regardless of how incorrect the elevation series actually is.
 "
He stated  that someone on the same cycling forum was shocked at the ascent/descent they had registered on a flat circular track.
My friend pointed out that this is part off the reason why the calories burnt counters on a lot of tracking devices mean diddlysquat as they cannot track effort ( ascent/descent) correctly.That is another subject however. I like my calories and would not be so discourteous as to count them.

Still no reply from Garmin. :o
Too little, too late, too bad......