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Author Topic: Not a bug, but a misdirection?! Error estimation of the UAV images...  (Read 255 times)

c-r-o-n-o-s

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Hello.

During a normal drone flight, it often happens that the GNSS correction fails for a short time.
Then the DJI RTK drones save these inaccuracies as values.
So far, this did not worry me, because these data are included in a compensation by Metashape.
And so far I have been able to really reproduce it.
Images with very poor positioning quality didn't have much influence on the result.

Now I noticed the following:
In the attached image I sorted the approx. 1200 pictures according to calculated accuracy.
I noticed that this deviates in some cases very much from the saved "DJI" accuracy. (See marked line)
If I deselect these images as reference, the result to my GCP is much better.

The stored values within the drone do not always seem to be correct. (Or with a certain time offset.)

Metashape should offer the possibility to take over the calculated accuracy.
At the moment I test this via "reference export" and immediate "reference import" with exchange of the DJI values against the calculated ones.

Do you have any experience so far?
« Last Edit: April 19, 2021, 10:08:05 PM by c-r-o-n-o-s@web.de »

Alexey Pasumansky

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Re: Not a bug, but a misdirection?! Error estimation of the UAV images...
« Reply #1 on: April 24, 2021, 03:24:06 PM »
Hello c-r-o-n-o-s,

If the coordinates are not measured accurately by onboard GPS, I think you should rely on the control points only.

You may perform some calibration flights over the area with precisely measured control points and take two sets of images: at first regular flight - taking photos in-flight, then custom scenario, when drone stops to take the photo. Thus you can check, if there's any time offset between the camera shutter and GPS device. If there's any, then I think the drone requires some maintenance, as the source of the problem should be fixed.
Best regards,
Alexey Pasumansky,
Agisoft LLC

c-r-o-n-o-s

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Re: Not a bug, but a misdirection?! Error estimation of the UAV images...
« Reply #2 on: April 24, 2021, 04:55:41 PM »
OK, thank you!

It's probably not so much a time delay, since most of the values are correct.
In this case, the RTK connection often failed. RTK ON/OFF/ON etc...
I think some pictures were not determined exactly...

Alexey Pasumansky

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Re: Not a bug, but a misdirection?! Error estimation of the UAV images...
« Reply #3 on: April 24, 2021, 06:49:19 PM »
Hello c-r-o-n-o-s,

If only some camera locations are measured incorrectly (and you can identify them somehow), you can uncheck those cameras in the Reference pane to avoid the use of their coordinates for georeferencing and optimization.
Best regards,
Alexey Pasumansky,
Agisoft LLC

c-r-o-n-o-s

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Re: Not a bug, but a misdirection?! Error estimation of the UAV images...
« Reply #4 on: April 24, 2021, 07:00:37 PM »
Until now, this has never been a problem.
Here it occurred for the first time.
However, I would have to "check" 1200 pictures soon.
It is not only the "good" or only the "bad pictures". It is the difference between the both values...

I'll wait for the next projects..
« Last Edit: April 24, 2021, 07:22:08 PM by c-r-o-n-o-s »