Author Topic: Recorded track show a lenght difference of 15% or more  (Read 1464 times)

Offline MKJJ

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Recorded track show a lenght difference of 15% or more
« on: September 16, 2019, 10:04:50 »
Hi,

some days ago I tracked a very short and easy tour. It is indicated with a lenght of 12 kilometers and around 350 hightmeters. The track indicates 14,5 kilometers! A difference of more than 15% is not acceptable. After importing the official track and my recorded track in a gpx editor both tracks look pretty much the same. How is this possible? How can I verify a recording? A deviation of 15% would make the device more or less useless.

Thanks in advance!
 

Offline poutnikl

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Re: Recorded track show a lenght difference of 15% or more
« Reply #1 on: September 16, 2019, 10:09:19 »
You can always throw the device out, if it became useless.. :-)

Is the recorded track path perfectly straight, or, does it have a little of zig-zag-ness originated from GPS fluctuation ?

As recorded track length calculation is based on GPS path, not the map way length.

You may try to set (stronger ) GPS filtering, that would straighten the GPS path
in Settings /GPS and sensors / advanced settings.

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Offline MKJJ

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Re: Recorded track show a lenght difference of 15% or more
« Reply #2 on: September 16, 2019, 10:28:02 »
I would call the track pretty straight.



This is the official track:



Seems to be pretty much the same.

See here the elevation profiles. First profile shows the official track, second profile show my recorded track:



Many satellites were available all the time. Connection was perfect.

I'm pretty sure that the official data are reliable. It's a very well known hiking tour for families and older people. Markings are perfect. A severe error like this is very unlikely.
« Last Edit: September 16, 2019, 10:31:48 by MKJJ »
 

Offline poutnikl

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Re: Recorded track show a lenght difference of 15% or more
« Reply #3 on: September 16, 2019, 10:53:30 »
The record track has to be examined in very high details, in range of meters, in sense how the recorded GPS positions are placed.

Note that Locus has no idea about the proper length about the route, as,in opposite of OSMAnd proprietary solution, the Mapsforge vector map libraries do not expose such information, AFAIK.

Try to check the length on online tools by uploading the GPX, what hey say?


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Offline erfi

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Re: Recorded track show a lenght difference of 15% or more
« Reply #4 on: September 16, 2019, 11:06:58 »
I see deviations in the pictures that could explain the difference.

 

Offline MKJJ

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Re: Recorded track show a lenght difference of 15% or more
« Reply #5 on: September 16, 2019, 11:37:42 »
Yes, there are some minor deviations. I measured the differences in my digital topo map. They sum up to around + 600 meters. Here is a detail of the track. Distance between waypoints is around 10 meters. Seems to be very straight.



The major difference between my recording and the official track is the number of waypoints (366 vs. 2700).

I have done many hiking tours in this area. Mostly, the recordings seem to be pretty accurate when it comes to distance. (accurate measurements of hightmeters seem to be problem). This is why I was surprised to see such a significant deviation.

Honestly, there is another reason for me to sort this out. I was hiking with my girlfriend. I said that we were pretty slow. She, on the other hand, found the hiking speed ok. Well, I'll leave the rest to your imagination.  ;D
 

Offline MKJJ

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Re: Recorded track show a lenght difference of 15% or more
« Reply #6 on: September 16, 2019, 11:48:44 »
Forgot to say: All online gpx viewers show the same lenght differences.
 

Offline Menion

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Re: Recorded track show a lenght difference of 15% or more
« Reply #7 on: September 16, 2019, 14:01:59 »
Hello,
shorty ... huge number of recorded points with small deviations sum in "huge" differences.

The suggested method for recording mainly in terrain with possibly worst GPS reception (high buildings, dense forest):

- reduce number of recorded trackpoints with "time interval" and "distance interval" parameters in recording profile. Imagine you walk usual 1 m/s, so times around 25 s and distance around 25 m are usually perfectly fine.

- you may try to enable horizontal filter in settings > GPS & sensors > location filter. Stronger filter > most probably shorter tracks that will anyway has little worst reaction on the quick changes in directions. Anyway for walking, even a strong filter should be perfectly fine.
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Offline MKJJ

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Re: Recorded track show a lenght difference of 15% or more
« Reply #8 on: September 16, 2019, 14:30:27 »
OK, thanks a lot for the valuable input. Will change the settings according to your suggestions. I've used the default settings so far. Strange that I had pretty good recordings in similar terrains. However, it makes sense to reduce the number of trackpoints. This might have a positive effect on the calculation of hightmeters. Will post the results.
 

Offline Menion

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Re: Recorded track show a lenght difference of 15% or more
« Reply #9 on: September 16, 2019, 14:37:16 »
and also a positive effect on your relationship with the girlfriend :)

If I remember correctly, default values should be 25 m and 5 seconds, right? Hmm, these 5 sec is probably too frequent.
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Offline MKJJ

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Re: Recorded track show a lenght difference of 15% or more
« Reply #10 on: September 16, 2019, 14:41:54 »
and also a positive effect on your relationship with the girlfriend :)

Oh, yeah!!  ;D