Orthomosaic generation errors

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

Hi there,

I am producing some Orthomosaic with pix4D, but there are many problems in it. For example:

  1. There are many distortions next to the buildings, as you can see:


or this image:

or this image:

when I check densified point cloud tor these areas, I can see there are some noises that are not placed at their actual height. Like this image:


The same problem exists in walls, and almost in all of walls and all of buildings I have this problems. The methods I use for editing these errors are:

  1. Draw a polygon in Mosaic Editing mode, and select best image

  2. Edit point clouds in RayCloud and delete noisy points.

  3. Drawing a surface on the roofs.

I wanted to know if there is any other methods to correct such errors? And actually it is not really possible to do this for an entire city. Is there anything special that I need to consider to get best results? I produced point clouds with high density and  full image size, that doesn’t help either. Is there any automatic solution for this? And finally what about the best software/package from even other companies to produce true orthophoto?

2

Hi Jim,

As the orthomosaic is generated based on the DSM that was created from Densified Point Cloud thereby it is expected that the noise and the artifacts from the first one will be reflected in the last. Hence I would recommend you to assess the quality of the images (blurriness, overlap, light variation, GSD) and the quality of the point cloud after 1st step before going to step 2 and 3.

Could you post here your quality report so I will take a look?

Thanks,

Ina

3

Dear Ina,

I think my situation is not really bad, check this report:

https://www.dropbox.com/s/nbu89l7twkiqdez/Ghorgh1_report.pdf?dl=0 

 

Thanks

Jim

4

Thank you for sharing the quality report.

The problem may come from the lower overlap in specific parts of your flight plan. I can see that in this areas you also have less density in matches which leads to a weaker reconstruction.

Have you tried adding some MTP’s in these areas?  In the following article, you can find how to mark Manual Tie Points around the model: 202560349.

Could you try and let me know?

 

Thanks,

Ina

5

Dear Ina,

 

Actually my processing area is not those areas, check this:


Also I tried to process only 3 lines with 7 image in each of theme, again same results. I think its a DSM generation problem, because when I use a perfect external point cloud, again these problems occurs. Check out this post
https://community.pix4d.com/t/6374-Rounded-edges-near-roof-even-when-I-use-external-perfect-point-cloud 

6

Thank you for the details. It helps me to understand the issue better.

The edges of roofs or lateral walls when flying at such altitude and nadir are not expected to be reconstructed. For this, you should use surfaces or choose a double grid flight plan so that all the facades of the buildings (north, west, south, east) are visible on the images

See: https://support.pix4d.com/hc/en-us/articles/202560449 

Please see the comment related to the external point cloud in the other post.

 

Cheers,

Ina