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

**URL:** https://community.pix4d.com/t/problem-in-back-projecting-the-densified-point-cloud-into-the-original-images/8541
**Category:** PIX4Dmapper Questions/Troubleshooting
**Created:** [July 8, 2019, 8:48am UTC](https://community.pix4d.com/t/problem-in-back-projecting-the-densified-point-cloud-into-the-original-images/8541 "2019-07-08T08:48:28Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![ciro\_potena](https://avatars.discourse-cdn.com/v4/letter/c/e274bd/32.png) [@ciro\_potena](https://community.pix4d.com/u/ciro_potena)
#### Post date: [July 8, 2019, 8:48am UTC](https://community.pix4d.com/t/problem-in-back-projecting-the-densified-point-cloud-into-the-original-images/8541/1 "2019-07-08T08:48:28Z")

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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** &nbsp;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&nbsp; **project\_name\_calibrated\_camera\_parameters** , Rx is the rotation around the X axis of the camera, and pt is&nbsp;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:&nbsp;

[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/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/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](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?

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### Author: ![Daniel\_Rico\_Cordero](https://sea2.discourse-cdn.com/pix4d/user_avatar/community.pix4d.com/daniel_rico_cordero/32/187_2.png) [@Daniel\_Rico\_Cordero](https://community.pix4d.com/u/Daniel_Rico_Cordero)
#### Post date: [July 12, 2019, 12:00pm UTC](https://community.pix4d.com/t/problem-in-back-projecting-the-densified-point-cloud-into-the-original-images/8541/2 "2019-07-12T12:00:45Z")

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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.

&nbsp;

&nbsp;