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Using distortion-corrected images problem

Images were taken using DJI’s Phantom 4 RTK.

In each of the two shots, a distortion-corrected image and a non-distortion-corrected image were obtained.

The error and image registration did not work properly because all the images obtained by the two shots were used and proceeded as one project.

What do you think of using distortion-corrected images when using the Pix4d mapper?

Also

What do you think about using the distortion-corrected and uncorrected images together?

Hi Kim,

You are probably refering to geometric distortion, am I right?

I do not really know how the DJI distortion correction works but Pix4Dmapper (and most of the photogrammetric software packages) work better with original images that do not have any correction algorithms applied. Photogrammetry relies on the reconstruction based on common features found in images, which are then transformed into keypoints and enable the stitching. Pix4Dmapper computes the distortion correction based on thousands of tie points which are generated automatically in Step1 and it is computed for all of the images at the same time, therefore there is a lot of redundancy.

Long story short, you just need a good image dataset (good lighting conditions so that the software detects the features correctly in each image) with good overlap, a high spatial resolution (i.e. small pixel size/GSD) and with a highly accurate geopositioning (if desired).

I would not include the distortion-corrected images in the processing, because Pix4Dmapper will take care of undistorting the images.

Cheers,
Teodora

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Thank you.
If so, the distortion-corrected image was extracted using the undistorted image storage function provided by PIX4D.

After that, when using the distortion-corrected image, is it possible to use the camera distortion parameter to reverse the distortion to create a result?

Also, what are the uses of distortion-corrected images?

Hi Kim,

I am not sure it is possible to reverse the distortion process in Pix4Dmapper. I personally never tried this and cannot provide pertinent information or advice.

To answer your last question regarding the usefulness of distortion correction: due to lens properties, images taken with almost all cameras are distorted and a correction step needs to be applied to process them properly. Pix4Dmapper estimates the distortion parameters for the camera during step 1.Initial Processing. These parameters are used internally to undistort the images. This step is crucial for generating an optimal 3D model.

I would suggest reading more about distortion correction here: Camera distortion.

Cheers,
Teodora

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thanks a lot.

but So, if you run the distortion-corrected image without putting any information about the distortion into other photogrammetry software, will the result be similar to the Pix4D mapper? (I’m talking about the problem of availability.)

Or, if you run the whole process again with the Pix4D mapper and the saved distortion correction image, will you get the same result as the image before the distortion at first? (When using a distortion-corrected image, all distortion parameters are written as 0.)

Hi Kim,

You can try to process the geometrically corrected imagery, but it is highly likely to get strange results with erroneous outputs.

The overall reason for the erroneous outputs is that distortion correction is not a standardized procedure that is uniformly employed across platforms. Often times the exact mathematics of this procedure is not publicly available and can vary from company to company. Thus, these corrections are not taken into account in the modeling of the camera parameters. Pix4Dmapper models the distortion of a camera by default and expects that distortion introduced by a lens to be present. When the distortion is removed prior to processing in Pix4Dmapper, then there are essentially two steps of distortion correction being applied in series, which is not ideal.

The reason that this may fail in Pix4Dmapper is that we place a very high value on accuracy of reconstruction and have a high threshold for what gets recreated with the resulting model. The inaccuracies introduced by pre-processing the images can skew the results to a level of inaccuracy that Pix4Dmapper is not going to reconstruct. Other applications that focus more on just generating something visually pleasant with the price of less accuracy may be able to complete processing this type of scenario.

As of now, processing undistorted images is not a supported workflow that we recommend for Pix4Dmapper. I would just recommend that you try it yourself to see the difference in the results.

As the correction of distorted images prior to importing them into Pix4Dmapper is out of my technical jurisdiction, I will let some other savvy users explain more about this process.

Hopefully this helps.

Kind regards,
Teodora

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