We use the drone to measure the length and width of animals at sea.

We have installed a lidar laser to get accurate height measurements needed to get precise calculations at the time photos and video are taken.

After testing on land and many flights at sea, we find that the gps time embedded in the picture, and the time of the controller runs out of sinc with the gps time.

We started the drone several times and took pictures over a period of several minutes at a time in front of a gps handheld (garmin) showing the gps time (in utc).
Depending on the time between flights, the time can be out of sync several minutes (after two days of not using the drone-controller.
Withing flights, the time sync remains constant, however the drift can be up to 15 seconds on different flights on the same day,  using the same controller - drone set, just changing batteries, and  closing and restarting the controller between flights.

online, people state the exif of the pictures are in gps time, but our experience so far tells us it isnt, at least not to the second.

We have cancelled automatic update of the time sync in the controller setting.

We have updated diferent firmware versions and have come across this problem for both our ph4pro setups.

Does anybody have experienced similar problems with the gps accuracy? and perhaps have a solution to this anoying problem?

the picture shows a php4 picture (original was dng format) of a garmin gps handheld showing time in utc, which differs 38 seconds with the photo exif data

Thanks,



M.

If you shot the photo in DNG, then there is a finite time taken to process the information then record it to the SD card, so I can imagine that there very well could be a time difference. But you should also consider that DJI do not publish any spec for time accuracy, as it is most likely not something they are concerned about.

Geebax Posted at 2018-8-11 15:52
If you shot the photo in DNG, then there is a finite time taken to process the information then record it to the SD card, so I can imagine that there very well could be a time difference. But you should also consider that DJI do not publish any spec for time accuracy, as it is most likely not something they are concerned about.

I am pretty late repliying here, Yes I agree initially with you GEEBAX,

however I found some more inconsistencies, photos with different offset times, when taking similar photos of a handheld gps which can run up to almost a minute...
Everytime i start up the drone / controller, the offset time is a little different...no consistency here

The same with video, looking at the start time, the time recorded in "properties / modified" seems the most likely to be the start time.
When you recoord a single video file, of say over 12 minutes, the timing of the first two videofiles match up, however, the third and fourth often do not match and in fact often appear to start during the previous videofile.

In my case video files have a max duration of 5 min 27 sec (just under 4 gb), so if you start with your 12 min video at 12:00:00, the second file starts recording at 12:05:27, then the third video should have a start time of 12:10:54, but often this time found under "modified", is earlier, which would mean that the videofile was created while the previous videofile was still recording.

the only consistency within flights is that there is a timing difference of 11 seconds compared to the gps handheld, between video and photo within a flight, likely to the data saving procedures.

does anybody know how to determine the exact start time of a video file?

Oceandrone Posted at 2018-8-30 05:13
I am pretty late repliying here, Yes I agree initially with you GEEBAX,

however I found some more inconsistencies, photos with different offset times, when taking similar photos of a handheld gps which can run up to almost a minute...

If you are continuously recording and the system is automatically splitting the files at the 4 GB boundary, then the next file will be created before the previous file finishes. To avoid this, don't keep shooting continuously, stop the recording from time to time.