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Problem in: back-projecting the densified point cloud into the original images

Dear all,

I am trying to back projecting the densified point cloud into the original images, but I found some issues. In the following, I describe the procedure that I am following:

Firstly, I import the point cloud (in XYZ format) and I subtract the offset read from the project_name_offset.xyz  file. Thus i transform the cloud points into the camera that of interest by using the formula shown in the code snippet. CalibData.cam_R and CalibData.cam_t are the position and orientation of the camera extracted from the file  project_name_calibrated_camera_parameters , Rx is the rotation around the X axis of the camera, and pt is the point that I want to back-project.

Thus, I transform the point from 3D to 2D according to the standard pinhole model and distortion parameters. Similarly, all the intrinsic parameters are the ones read from the project_name_calibrated_camera_parameters file.

All the formulas I used are the ones described in the pix4d tutorials here: 

https://support.pix4d.com/hc/en-us/articles/202977149-What-does-the-Output-Params-Folder-contain#label12

https://support.pix4d.com/hc/en-us/articles/202559089-How-are-the-Internal-and-External-Camera-Parameters-defined

https://support.pix4d.com/hc/en-us/articles/202977149-What-does-the-Output-Params-Folder-contain#label2

The result is the following:

The images are slightly misaligned. I also tried by removing the Rx transformation but the output is even worse. What am i doing wrong?

Hello Ciro,

I think what you are doing is correct.

The only thing is that, after applying these formulas, you should back-project the densified point cloud into the undistorted images (not the original ones).

Pix4D can export those images when running Step1:

Regards.