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Issues with Distortion on Top Down Photos with -90 Pitch

austin1124

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Hi all,

I take a lot of photos with the pitch set at -90 top down, and recently I have noticed a lot of distortion on the photos and I am uncertain how to fix them. I take photos of basketball courts, so you can clearly see it with the lines. I've attached two photos, one from a batch two months ago where there is no distortion (0899) and one recent one where there is clear distortion (0053). I've tried recalibrating the gimbal, the IMU, compass and everything else, but I can't seem to figure out what is causing this. Here is the EXIF data on each as well. Any help would be appreciated.

0899
Gimbal Roll Degree : +0.00
Gimbal Yaw Degree : -146.70
Gimbal Pitch Degree : -90.00
Flight Roll Degree : -1.40
Flight Yaw Degree : -150.80
Flight Pitch Degree : +0.80

0053
Gimbal Roll Degree : +0.00
Gimbal Yaw Degree : -90.40
Gimbal Pitch Degree : -90.00
Flight Roll Degree : +6.20
Flight Yaw Degree : -83.90
Flight Pitch Degree : -3.70
 

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  • DJI_0053.JPG
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  • DJI_0899.JPG
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You are taking pictures with a wide angle lens so depending on the distance straight lines will look distorted, the closer you are the more distortion.
You could try taking them from a greater altitude then cropping the photo.
 
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You are taking pictures with a wide angle lens so depending on the distance straight lines will look distorted, the closer you are the more distortion.
You could try taking them from a greater altitude then cropping the photo.
I guess what I didn't mention is that both of these are at the same altitude, almost, about 90m. It's just strange because I've taken thousands of similar pictures with no distortion issues, but every single one I take has the issue over the last month, so it feels to me like there is some new hardware or software problem.
 
I've attached two photos, one from a batch two months ago where there is no distortion (0899) and one recent one where there is clear distortion (0053).
It might help if you explain what kind of distortion you think you have because whatever it is, it's too subtle for me to see.
I've tried recalibrating the gimbal, the IMU, compass and everything else
Why recalibrate the IMU and compass?
They can't have any influence on any kind of distortion and if the drone s flying properly, they are calibrated properly.
 
It might help if you explain what kind of distortion you think you have because whatever it is, it's too subtle for me to see.

Why recalibrate the IMU and compass?
They can't have any influence on any kind of distortion and if the drone s flying properly, they are calibrated properly.
I added guides so maybe it's a little clearer--on the one photo you can tell the lines match the guides and are very straight, on the other they don't at all.
 

Attachments

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Yes--the issue persisted across an entire batch of photos/locations where the lines were straight
 
I don't think that's distortion - it looks like the gimbal pitch is slightly off. The view in the "distorted" photo is what you would expect if the actual gimbal pitch were a few degrees less than 90°, so the camera is not looking directly down, but instead slightly forwards.
 
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I don't think that's distortion - it looks like the gimbal pitch is slightly off. The view in the "distorted" photo is what you would expect if the actual gimbal pitch were a few degrees less than 90°, so the camera is not looking directly down, but instead slightly forwards.
This makes the most sense to me as well--as it is more pronounced when rotated (whereas if it was truly top down this would not be the case). The pitch in the EXIF clearly says -90, so is there any way to fix it other than a gimbal recalibration?
 
This makes the most sense to me as well--as it is more pronounced when rotated (whereas if it was truly top down this would not be the case). The pitch in the EXIF clearly says -90, so is there any way to fix it other than a gimbal recalibration?
I don't think that you can manually calibrate gimbal pitch, so I would try the gimbal calibration again, making sure that the aircraft is on a completely level surface.
 
I don't think that you can manually calibrate gimbal pitch, so I would try the gimbal calibration again, making sure that the aircraft is on a completely level surface.
Yeah, I've tried this about 4 times on surfaces that are extremely flat without any change in the results. I don't know if there are any other options or if contacting DJI support and sending it to them for repair would make sense. Either way I appreciate the feedback.
 
Yeah, I've tried this about 4 times on surfaces that are extremely flat without any change in the results. I don't know if there are any other options or if contacting DJI support and sending it to them for repair would make sense. Either way I appreciate the feedback.

Just to be sure, not just flat but level, ie. no tilt in any direction.
 
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For better rectilinear results with the wide angle lenses that DJI uses, the various image transform tools in Photoshop or Lightroom are necessary to use in post processing. Wide angle distortion and slight perspective problems from the gimbal not being perfectly parallel to the ground below are easily compensated for.

Note as well that if the ground below the drone is not perfectly flat, as in any kind of incline, this too will introduce perspective distortion even if the gimbal is set to 90 deg to the horizon.
 
Looks like a simple case of parallax to me, either the camera wasn't set pointing directly down & in the centre of the intended picture or the ground is not level.
 
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In the first photo, the backboards are fairly even from one side to the other, the second they are skewed so as mentioned earlier, either terrain or aircraft position are inducing parallax error.
 
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