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What does Merge Projects do?

Hi, I am planning to fly a site and I anticipate that I want to use Merge Projects. I will fly two flights of the same area. I know from experience that Pix4D has a tough time combining images from multiple flights, but when each flight is processed individually, it seems to do fine. Therefore, I plan to use Merge Projects.

Does Merge Projects actually allow each project to inform each other for an improvement on the resulting point cloud and mesh? Or is it simply a registration algorithm that preserves the individual projects and only stitches them together? If it is the latter, then I will simply fly one flight instead of two.

For example, I have the following three projects:

As you can see, the first project is having difficulty with the elevation of the roadway. The hope was that when I merged the projects, the second two projects would inform the first that it is in error. Here is the result of the merged project:

It seems that Merging Projects does not help the accuracy, but simply keeps the tie points of each sub-project rigid, and just rotates and translates the sub-projects to register them together. Is this correct?

Hi EvanH,

Yes, the merging procedure is not used to correct/improve the accuracy but rather to

  • merging different image acquisition types such as terrestrial and circular and grid
  • merge two subprojects that were split because of limited capabilities of processing resources (large projects or low-end device)

In the merging article in our Pix4D Documentation, we suggest the following:

It is very important that before merging, all subprojects are processed successfully and there are no issues reported in the initial checks of the quality report, e.g. bad camera optimization, uncalibrated camera or multiple blocks.

I hope this information helps.