Wrong vertical speed and 2D speed

[sbonaime]

Hi,
on my mac, with this Hero8 black footage
https://drive.google.com/file/d/1632G6hBeecq4KH8ukYSYOSU1RvS-v53G/view?usp=sharing
and using gopro2gpx and https://djitelemetryoverlay.com/srt-viewer I can see that the vertical speed is going from -448 to 335 km/h and the 2D speed reach 1576 km/h

With https://goprotelemetryextractor.com/free/ and the same footage vertical speed is correct from 0 to 8.34 km/h and the 2D speed reach 29 km/h

here is my command line. I used #15 version but it did not change the problem

gopro2gpx -v GH011227_saut.MP4 test
Working on file GH011227_saut.MP4 track 3 (Stream #0:3(eng): Data: bin_data (gpmd)
GPSFIX change to 3 [lock 3D (ok)]
-- stats -----------------
- Ok:                202
- GPSFIX=0 (bad):      0 (skipped: 0)
- Empty (No data):     0
Total points:        202
--------------------------
Working on file GH011227_saut.MP4 track 3 (Stream #0:3(eng): Data: bin_data (gpmd)
GPSFIX change to 3 [lock 3D (ok)]
-- stats -----------------
- Ok:                202
- GPSFIX=0 (bad):      0 (skipped: 0)
- Empty (No data):     0
Total points:        202
--------------------------
```

ffmpeg version 4.4 Copyright (c) 2000-2021 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.29)

ffprobe version 4.4 Copyright (c) 2007-2021 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.29)

[Simske]

I just checked the elevation and speed data:

and everything seems fine there.

I'm guessing the problems comes from the time data: the time for every trackpoint is resolved to a second, but there are 20 trackpoints per second. When calculating the speed from elevation and location data this can lead to high numbers (or division by 0 error).
I don't know if the Gopro data has a higher time resolution which is just not outputted by gopro2gpx, otherwise you would need to just interpolate the time data inside of a second.

[sbonaime]

files size from
gopro2gpx 58k
https://goprotelemetryextractor.com/free/ 81k
In the begining of gopro2gpx gpx file, I can see that my camera is a gopro7-track. With goprotelemetryextractor it is a HERO8 Black.
It may explain why...
@Simske can you send my the gpx file you get ? Did you try to plot it with https://djitelemetryoverlay.com/srt-viewer ?

[Simske]

@Simske can you send my the gpx file you get ? Did you try to plot it with https://djitelemetryoverlay.com/srt-viewer ?

Yes, when I put it in I get the same results as you, so I assume our outputs are the same.

I just compared the files from goprotelemetryextractor.com and gopro2gpx, the data for a single trackpoint look like this:
goprotelemetryextractor.com:

<trkpt lat="46.0098989" lon="-1.3977705">
    <ele>0.514</ele>
    <time>2020-10-29T11:03:38.558Z</time>
    <fix>3d</fix>
    <hdop>104</hdop>
    <cmt>altitude system: MSLV; 2dSpeed: 7.301; 3dSpeed: 7.31</cmt>
</trkpt>

gopro2gpx

<trkpt lat="46.0098989" lon="-1.3977705">
    <ele>0.514</ele>
    <time>2020-10-29T11:03:38Z</time>
    <extensions>
    <gpxtpx:TrackPointExtension>
        <gpxtpx:hr>0</gpxtpx:hr>
        <gpxtpx:cad>0</gpxtpx:cad>
        <gpxtpx:speed>7.301</gpxtpx:speed>
        <gpxtpx:distance>0</gpxtpx:distance>
        </gpxtpx:TrackPointExtension>
    <gpxx:TrackPointExtension/>
    </extensions>
</trkpt>

As you can see from this:

• I was right about the timestamps, resolution of 1 second is not enough
• Speed and other additional data is written into a comment tag for goprotelemetryextractor, while gopro2gpx uses the Garmin GPX-extension to save only the speed.

I haven't worked directly on the decoding part of this package, maybe @juanmcasillas has an easy fix.

[sbonaime]

@Simske I am diving into the code and I see a problem. The GPS decoded data we get does not have any millisecond data from Hero8 MP4 thus we have 20 points with the same datetime as you saw.

[younes-mirinezhad]

@Simske I am diving into the code and I see a problem. The GPS decoded data we get does not have any millisecond data from Hero8 MP4 thus we have 20 points with the same datetime as you saw.

I have the same problem.
is there any solution?

[Simske]

@younes-mirinezhad No sorry, I didn't have time to look at it yet

[JimmyS83]

Could you try with PR#24 ?

[FreudBH]

Hello!
I noticed in the Update section "Added support for 18Hz resolution in GPS5 fourCC, to fix (#PR23,#PR17)[https://github.com//pull/24]. Thanks to (JimmyS83)[https://github.com/JimmyS83] for spot the problem."

Nevertheless I just run the last version and the speed is being calculated wrong. I am using GoPro Max 360.

GH010015_1717275916188.gpx.txt