desktop, pix4dmapper- Annotate to remove background -

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

I am having difficulty to understand how to remove the background from my project using annotate.  Need help.

 

This is the camera distribution and the model on a rotary table.  I think the noise is coming from the background on which the shots are taken.  A plain white sheet.

 

This is what the noise looks like that I am trying to remove.

 

I have touched one of the noise points that is not on the model.  This is the  ray cloud it generated.

 

DSC_0071.jpg  is the image shown in the image  below that I chose to annotate.  It only  shows the background

 

This is the area (red) that I selected to be carved.

 

This does remove noise but it also removes parts of the model so after applying it the model will end up with holes in it.

I am quite sure this arises out my misunderstanding of how annotation works.

Any enlightenment or suggestions for how I can figure this out and make it work would be greatly appreciated.

I think I have read and watched most videos I can find but I am still not getting it.

Thanks

Doug 

2

Hi Doug,

With regards to your first question about why you can see only the background, it looks like you have zoomed in too much in the image DSC_0071. For finding all the pixels that need to be annotated, You would need to zoom out a bit to see the image other than the background wall. It looks like you have zoomed in too much. 

This article explains how to use the annotation tool in Pix4D. _In order not to create holes in the final model, the Image Annotation tool should be used on images where only  one  3D point is located on the ray connecting the camera center and the annotated pixel. _You will also find more information here. The Carve annotation deletes all the 3D points that are located on the rays connecting the camera center and the annotated pixels.  That means that you should be very careful not to penetrate the point cloud and create holes in the model when using it. Image Annotation tool can be very useful to remove 3D points of the sky or horizon when dealing with oblique imagery.

In some tiny parts of ray-cloud, you may also find it easier to edit some points manually. We suggest you combine both methods to achieve satisfying results. For more information: https://support.pix4d.com/hc/en-us/articles/202560499-How-to-edit-Point-Cloud-Points-with-the-rayCloud (you can select the points and then delete them: assigning them to the “deleted group”).

You could also look at this article that describes how to remove noise from the Point Cloud: 
https://support.pix4d.com/hc/en-us/articles/204085149-How-to-remove-Noise-from-the-Point-Cloud 

3

It will be far easier to change the way you take pictures and setup Pix4Ddesktop settings than using annotations to remove background noise…I know from experience that it takes less time to re-shoot and re-process than cleaning with the annotation tool.  This image is a “no-no” for any photogrammetry software to deal with background noise but it can be done with zero noise in the point cloud with zero edits.

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