Undistorted Images Detected

PIX4Dmatic
1

I’ve been having the following warning message pop up every time I import images from my drone.

“Undistorted image detected. Using such images is not recommended for photogrammetry.”

Drone is a DJI Mavic 3T and I’m using 3000x4000 resolution RGB photos. This warning message started popping up around a half a year ago, however I just ignored it since the rest of the photogrammetry process worked without any issues. My questions is, why is this warning message coming up? As far as I know, the images that are taken off the drone are not modified in any way (aka undistorted).

2

Hi nlawrence,

Pix4D software is designed to process raw, uncorrected images. Some DJI drones offer a “dewarp” or distortion-correction option in the controller—this should be disabled before flying. If pre-corrected (dewarped) images are used, the camera model in Pix4D no longer matches the imagery, which can lead to calibration errors and degraded outputs.

3

I’ve gone through the settings in the drone and I haven’t found any dewarping option to turn on and off. To clarify this is the 3T model and it seems the menu options between the 3E and 3T variants differ.

4

The dewarp is certainly there for the 3 multispectral. But if you are getting this warning, then likely the image exif is tagged. However, at this point, it is hard to comment on what exactly is going on with the images.

5

Hi @nlawrence as mentioned by Mike, this warning in PIX4Dmatic is triggered when the software detects metadata tags (XMP) indicating the images have already been ‘dewarped’ by the drone’s firmware. Since you started getting warning messages about a half year ago, it’s possibly due to a DJI firmware update.
Photogrammetry works best on raw, distorted images so that our algorithms can model the lens geometry accurately. However, in most cases, PIX4Dmatic can accurately reconstruct the scene anyway, and one of the only ways to assess the accuracy of your results is with check points. So if your results are good, you can continue ignoring the warning.

6

That’s what I’ve figured. I’ve been using it with this error for a few months and the reconstructions look fine.