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Pix4d Creates Multiple Overlapping Surfaces

A colleague of mine has run into an issue of Pix4D desktop creating overlapping surfaces.  He and I worked on the problem together yesterday, but could find no glaring errors.  There are four flights using a Phantom 4 Pro at 400ft.  80% overlap. 

Where the 4 flights overlap Pix4D is creating two identical surfaces.  The surfaces are identical except for they are separated vertically by 10 to 60 feet.   The project has sufficient GCPs that were surveyed in with survey grade GPS.  No issues with the GCPs were noticed.

Anyone come across this before or have any recommendations?

Without looking at the Quality Report, my guess is poor overlap that MTPs might fix or a change of settings in Step 1.  The Quality Report will list more than one block on the first page if this is the issue…otherwise there isn’t enough info to go further into troubleshooting.

Thanks for responding Adam. Below is the first page of the quality report.

Troy, your keypoints and matches look great so you probably have good settings in Pix4D.  Of course the issue is the 8 uncalibrated pictures that is likely resulting in the 2 blocks.

You need GCPs or MTPs to tie in those uncalibrated pictures as the first step.  After that there still might be some need for more MTPs to get both blocks as one.

Somebody else might have a better idea but that is all I see without getting more pictures.  And I have to admit that other photogrammetry software has problems like this but not normally Pix4D in my experience.

I agree with Adam that the two blocks are probably part of the problem.

If I correctly understood the 4 flights were processed together in the same project. In such cases, it can happen that if the flights were flown in different lighting conditions (e.g. because it was flown at a different time of the day) that the software cannot recognize the overlapping area between flights as being the same, which can result in two layers in the reconstruction. 

As Adam mentioned, adding MTPs should help. I would even go as far as directly doing the merging procedure, i.e. process each flight separately for step 1, including MTPs on the areas that are overlapping with adjacent flights and then merge them. The process is described here: https://support.pix4d.com/hc/en-us/articles/202558529

Let us know if you could fix the issue and how! :slight_smile:

Hello Everyone, Same thing happens to my data sets. I got 254 with good overlap, I am sure since my landing site is the highest point in the project area. And I set 80% overlap. Basically, everything is okay, The horizontal component is okay but the vertical of two blocks has a difference of up to 6 meters.

This is the data where I got 5 meter difference in elevation but there is no problem on horizontal.

@Roy: please add the information for your project in the thread you have created and we discuss it there, otherwise we will mix up the two issues: https://community.pix4d.com/t/3387 Thanks!