JUNSUN S100G metadata

[gduck]

Hi!

I can't extract correct GPS data from my car camera movies. Do you have any opinion?

An example:

Correct GPS datas:
GPSDateTime = 2019:01:14 16:10:57Z
GPSLatitude   = 48.07251 
GPSLongitude = 19.78416
Speed: 46.73 <-- this is OK!

Extracted data with exiftool:

+ [GPS directory, 32768 bytes]
  |   608000: 00 00 80 00 66 72 65 65 47 50 53 20 4c 00 00 00 [....freeGPS L...]
  |   608010: 78 2e 78 78 00 00 00 00 00 00 00 00 00 00 00 00 [x.xx............]
  |   608020: 30 30 30 30 30 00 00 00 00 00 00 00 00 00 00 00 [00000...........]
  |   608030: 10 00 00 00 0a 00 00 00 39 00 00 00 e3 07 00 00 [........9.......]
  |   608040: 01 00 00 00 0e 00 00 00 41 4e 45 00 90 19 a6 43 [........ANE....C]
  |   608050: 46 ec 0b 45 2f dd c9 41 d7 a3 00 41 00 00 00 00 [F..E/..A...A....]
.......
  |     [snip 30736 bytes]
  | GPSDateTime = 2019:01:14 16:10:57Z
  | GPSLatitude = 3.53666178385417
  | GPSLongitude = 22.6461181640625
  | GPSSpeed = 46.7315156326294
  | GPSSpeedRef = K
  | GPSTrack = 8.03999996185303
  | GPSTrackRef = T

Thank you for your help, best regards:
    Csaba

[StarGeek]

Can you make a short sample video available? 

[gduck]

Yes, of course! Thank you for any help!

https://data.hu/get/12557120/2019_0114_161055.MOV

[Phil Harvey]

Hi Csaba,

I got the sample and I'll take a look at this as soon as I can.

Unfortunately, recently I've been receiving a number of videos where the GPS information seems to be obfuscated in some way.  I hope this isn't the case here, but the fact that ExifTool extracts it with the incorrect values is a bit worrisome.

- Phil

[gduck]

Hi Phil!

Thank you for your help But, if it is a unique "Chinese" encoding (and not used on another device), don't waste your time!

I also tried to encode, but I have no practice in it

[Phil Harvey]

I've done a bit of work on this but haven't figured it out.  The lat/lon really look like they are stored as 4-byte floating point values, but the numbers don't make much sense.  There seems to be a scaling and an offset applied which is different for the latitude and longitude.  Attached are the raw floats as decoded from the file, and plots of these numbers.  Here are the ranges for the actual and raw values extracted as a float:

Actual latitude: 48.07251 to 48.07695
Actual longitude: 19.78416 to 19.78866

Raw latitude: 332.198699951172 to 332.212097167969
Raw longitude: 2238.76708984375 to 2238.77514648438

- Phil

[gduck]

Hi Phil,

thank you! 

Yes, I also not found the decoding logic

Thank you again!

PS: I can you only use one program with correct GPS datas: JMS DVR GPS PALAYER V3_2.18. But there are a lot of annoying BUGs in this program.