No exact track backup possible

Ingo Rau shared this problem 3 years ago
Not a Problem

My track.db is getting ever bigger and takes longer and longer to load, especially on my old devices (S4). I also synchronize the file between devices and my NAS.

So I wanted to delete some older tracks, but of course made a backup first. Just to be sure, I tried to reimport some of the backups - but the result was not identical. Not only was the "Track created" date different (which I can understand, technically), but the number of points was a little less than the original. Even some stats differed slightly. Apart from GPX, I tried KML and TCX (all other looked to me like they're not suitable at all), but that was even worse.

Am I doing something wrong or is that a bug? Is there any way to do a backup in a way that I could later reimport the tracks and have everything the way it was before (apart from the created date, perhaps)?

Comments (7)

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Hello Ingu,


based on my knowledges, GPX v 1.1 should be best possible format to store recorded tracks without any loss of information.


I've just tried to export own 65 km long track and reimport it back and statistics screen match perfectly. Even a "Created date" is same as before, no change.


Hard to say ... you should try to attach screenshot before export and also attached GPX and I'll check if I get same result or better, if I get any idea :).

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Hi Menion,

thx for trying. I don't have the time to do some further tests, but will asap. I didn't attach the GPX because if the problems in the export already, that wouldn't help.

However, one thing I forgot to mention: The original track was already an import - I didn't try it with a track recorded with Locus. I might have the original GPX used for import somewhere - I edited the track after that, but perhaps with the original, it's possible to reproduce.

Stay tuned ;)

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Hi again!

I finally found the time to look at this again, and now I have an example to reproduce. Files are in the attached ZIP.

What I did:

  1. Import "2013-08-17 Original.gpx" into Locus
    -> Track statistics in Screenshot "2013-08-17 Imported.png"
  2. Export track as "2013-08-17 Exported.gpx"
  3. Import this track again
    -> Track statistics in Screenshot "2013-08-17 Reimported.png"

As you can see, the stats differ slightly, especially there are 13 points missing in the reimported track. Also, the screenshot "Track list.jpg" shows that the original import got the correct date (05/09/2013), whereas the reimport got today's date. You can also see that on the Information tab of the tracks (no screenshot).


I know, it's only minor differences, but it worries me a little, as it's so hard to tell with GPX what exactly is different. And this is definitely not the only track I experienced this with.

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Hello Ingo,


thanks, I'm testing it.


Check original file line 1076 and in exported file line 1080. There are two same points. You may see that Locus exported these points with reduced accuracy to six decimal numbers in coordinates. Difference between original coordinates of point on same line and point below is 9 milimetres! (so nothing compare to GPS accuracy). Distance in exported file is anyway equal 0! During import, Locus ignore points that has 0 distance to previous point and here is lost 13 points => 13 points that were on exactly same place after rounding of coordinates during export.


Time "created" will be improved in next version.


So I generally think that this is not a problem, because rounding of coordinates has really zero effect on quality and accuracy of exported track.

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Ok, yeah, that's a very good explanation :)

As you can see in the comment, that track wasn't created with Locus - I just tried another track that was originally created with Locus, and there was no difference (apart from the created date).

So thanx, happy again, I can clean up my db without fear I might lose something.

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to be 100% sure, suggest to do a complete backup over Backup manager and keep it once a time. It's always good to have a backup of backup :).

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Hi,

My simple question: On both tracks I see 1814 trkpt's.

Statistics report is not correct. No big issue. Agree.

Why a difference in the statistics report screen? 1814 <-> 1801.

Yes I did read that Locus ignores 13 points.


Just a remark.

Regards.

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Don't understand. Difference between imported tracks is 13 points, because Locus considered these 13 points as identical and skipped them during import.

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Example files Ingo: 1. Original gpx= 1814 trkpts. 2. Exported gpx (by Locus) = 1814 trkpts.

There is no difference in the total trkpt's in both files !

Reimport that "Exported gpx" (by locus) :

Locus "internally" skips 13 points (considered identical) not to be used for display. (no problem)

(+/- Identical: 13 points are very similar in coordinates but different in timestamp)

Locus statistics screen should report:

The total trackpoints in the file: = 1814 trackpoints.

(Other softwares I tested reports are correct)

Similarity with elections: 1814 people are present for the votings. (fact)

Counting the votes 13 out of 1814 are not accepted (invalid) votes. (judged)

In final report you can't say that that only 1801 people has voted.

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In final report I say that 1801 people votes, others (13) were kick out. Still don't get point, what is wrong, sorry.

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