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2 Missions flown at 200 ft Max, while the 3rd flown at 50ft max (due to FAA altitude restriction)

I have 3 UAV missions for a Site flown with a Dji M200.  2 of the 3 UAV missions were flown at 200ft max, while the 3rd (due to FAA altitude restrictions) was flown at 50ft.  I am seeking guidance on how to manage these correctly in Pix4D. 

I am thinking that I process the two 200-ft altitude missions in Pix4D together.  I would process the 3rd (50ft max) mission separately.  Then I would merge them into a 3rd Pix4D project using manual tie points. 

I am just seeking a 3D point cloud at the end of this to use in Civil 3D, as I realize the ortho-imagery won’t stitch correctly due to the different altitudes.



Hello Pix4D support.  Can someone please respond to my request for guidance?  It has been over 2 weeks.





Hello Michael,

There is an article in our Knowledge Base which talks about different pixel sizes in the same project: Can Pix4Dmapper process images taken at different flying heights?

As you can see there, the difference should not be larger than GSD1 ≤ 2 * GSD2.

This is an approximate rule of thumb as it also depends on other factors. For example, it is very likely that you can process together two projects with GSD1=2 cm and GSD2=6 cm (where the pixel size is three times larger). But most probably you will not be able to process a project with GSD1=30 cm and GSD2=50 cm for example (where the difference is not even two times as larger).

What you propose sounds reasonable (creating a project with the 200 ft projects and merge it to the 50 ft one)  to me but be aware that in case the difference is very large, the software might not be able to merge both projects and you will have to mark many manual tie points. Even so, it might happen that two blocks are created and therefore, there might be “jumps” in between the 2 point clouds. In adition, as the GSD is different, the density will be different too.

I hope this information helps.

Thanks Daniel,

Yes this was certainly not an ideal situation and I paid for it when trying to merge the two projects.  I definitely saw the “jump” you mentioned right at the line in the sand between the 2 projects. 


Project #1 (higher altitude) had a GSD of 1.45cm, while Project #2 (lower altitude)  had 0.45cm GSD.  Therefore, the “jump” I was seeing (despite marking several MTPs along the project interface), must be attributable to the “_GSD1 ≤ 2 * GSD2” rule of thumb _you mentioned above.  Live and learn…thankfully, I had surveyed in the low-altitude area with GNSS, so I got “backup” data :slight_smile:


Thank you for your help.





Thanks for the feedback and good to hear that you have backup data.