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Bug report: overall ascend/descend value is wrong
#1
I checked two tracks, both are bigger than the real value.
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#2
Hi jolt2000,

please provide more information to reproduce your problem. It's impossible to help without.
--
Christian
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#3
Hi,

Please check attached track, RouteConverter shows in this track the overall ascend/descend are 2370 and 2416, but the two values are too big. In another track web the two value are 1047 and 1090. From my experience of hiking, I know the values should be about 1000.

The version is 2.11. Thanks.


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.zip   11-17-13.zip (Size: 53.41 KB / Downloads: 603)
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#4
(20.11.2013, 06:02)jolt2000 Wrote: Please check attached track, RouteConverter shows in this track the overall ascend/descend are 2370 and 2416, but the two values are too big. In another track web the two value are 1047 and 1090. From my experience of hiking, I know the values should be about 1000.

Let me explain the difference between the values: RouteConverter just naively sums up positive and negative deltas between positions. You can watch this if you make the Ascend and Descend column visible. This gives the values 2370 and 2416 you are observing.

These values differ from reality for two reasons:
  • the tracked positions of your track are value close to each other
  • consumer GPS devices aren't that accurate and produce a lot of noise, i.e. different latitude/longitude/elevation values for the same position
You can see these two effects like this:
  • If you choose Complete->Elevation for all positions and use date from the NASA SRTM3 project instead, the Ascend/Descend decreases to 1636/1676.
  • If you choose Position/Delete Duplicate Positions.../Select redundant positions/20m threshold and 'Delete selected positions' the Ascend/Descend decreases to 1290/1330
I hope this explanation helps?
--
Christian
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#5
Hi Christian,

Thanks for your detailed explanation, although I don't quite understand it. Smile I don't know such gps term as NASA SRTM3 and why it is related with date. But I understand it is an issue of algorithm.

In my thinking, the total ascend should be sum of ((delta = ph(n) - ph(n-1)) > 0? delta : 0), but now I know it is not so simple.

I used to upload my track to a track web, so I am surprised when I see the total ascend/descend are so big in RouteConverter. Looks like it is just about different algorithm.
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#6
(21.11.2013, 11:12)jolt2000 Wrote: I don't know such gps term as NASA SRTM3 and why it is related with date. But I understand it is an issue of algorithm.

Not exactly: NASA SRTM3 is the project name of a mission to create an elevation database for the world. When you use RouteConverter's Complete->Elevation function, it's replacing the rather inaccurate GPS elevation information which more accurate, smoothed elevation data for the NASA SRTM3 database. Just follow the instructions in my previous post to see the effect with your file: If you choose Complete->Elevation for all positions, the Ascend/Descend decreases to 1636/1676.

(21.11.2013, 11:12)jolt2000 Wrote: In my thinking, the total ascend should be sum of ((delta = ph(n) - ph(n-1)) > 0? delta : 0), but now I know it is not so simple.

What RouteConverter does is exactly this simple approach: RouteConverter just naively sums up positive and negative deltas between positions. You can watch this if you make the Ascend and Descend column visible.

(21.11.2013, 11:12)jolt2000 Wrote: I used to upload my track to a track web, so I am surprised when I see the total ascend/descend are so big in RouteConverter. Looks like it is just about different algorithm.

Propably the "track web" is using a more sophisticated algorithm?
--
Christian
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