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Author Topic: Wrong allignmento after adding markers: why?  (Read 516 times)

Gstudio

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Wrong allignmento after adding markers: why?
« on: August 10, 2022, 11:56:41 AM »
I have a problem with image alignment, let me explain.
From DJI Mavic Mini I acquired 550 photos in order to create the orthophoto of a fairly large area (about 70,000 square meters). Before proceeding with the flight I detected several markers positioned on the ground using a GNSS antenna.
The first thing I did was to create a chunk and have Metashape do the alignment of the images in order to get the scattered cloud (without using the markers). The initial result is excellent, only 3 images did not align (I am on the seashore and I expected that all the images taken on the water would not be aligned, instead only 3 were excluded). Subsequently I proceeded to place the georeferenced markers on all the images in which they appeared, then I relaunched the alignment by resetting the previous one. In this phase I gave both SOURCE and then SEQUENTIAL as a method to compare the differences. After these calculations the misaligned images are much more. Because? The coordinates of the markers derive from a topographic survey, so they are all correct and the points are assigned correctly in all the photos.
I wonder why without markers the alignment was correct, while adding them many images are no longer aligned.

Paulo

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Re: Wrong allignmento after adding markers: why?
« Reply #1 on: August 10, 2022, 12:12:02 PM »
Gstudio,

after placing the markers and ticking them, you need to do optimize and not reset alignment as your current alignment is correct but the introduction of GCPs will only refine the alignment to its correct position according to GCPs. Also  please check the  CRS of GCPS and cameras are they the same or different?

You can always shre the aligned project in psz format for  us to have a look at...
Best Regards,
Paul Pelletier,
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Gstudio

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Re: Wrong allignmento after adding markers: why?
« Reply #2 on: August 10, 2022, 12:29:56 PM »
Today I'll try agains with optimization.

I proceeded with the alignment reset because I have also noticed on other works I have done in the past that the error on each marker is generally lower if I do the reset instead of the optimization.
The images were all captured by drone in the same flight.

Gstudio

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Re: Wrong allignmento after adding markers: why?
« Reply #3 on: August 10, 2022, 12:37:51 PM »
Just a question. Can I copy all reference settings to first allignement? (1st is the alignment done without markers, I have this project saved). I would not like to reposition all markers on all photos........

Paulo

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Re: Wrong allignmento after adding markers: why?
« Reply #4 on: August 10, 2022, 12:53:57 PM »
HELLO,

in the chunk with markers placed just save them as xml and then import them into first original alignment. the markers will appear with their positions marked on each photo...
Best Regards,
Paul Pelletier,
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Gstudio

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Re: Wrong allignmento after adding markers: why?
« Reply #5 on: August 10, 2022, 08:09:53 PM »
Thanks to all you!!!