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Author Topic: Issue with Alignment in Photogrammetry rig  (Read 863 times)

elliotdenlady

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Issue with Alignment in Photogrammetry rig
« on: November 06, 2020, 06:36:29 PM »
Hey there,

 I work at a university and i've trying to work with a 60 Esper camera rig set-up. I have been having an issue where when I try to align the photographs, Metashape is really struggling and almost every time will align them as if all of the cameras are on one side of the room. I realise there must be an issue with the photographs I am inputting or the environment I am shooting them in.

 There has been some issues with focal length (the dslrs are APS-C frame size but they have 50mm standard lenses) due to the fact the room i'm working in is quite small. So I suspect there isn't enough coverage for the photographs to align properly. I am wondering if that is the main cause of this issue?

The photographs I am inputting are all consistent and should work fine with photogrammetry (I think anyway!)

Can anyone help me with why this might be happening? I'm quite stuck !



badger

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Re: Issue with Alignment in Photogrammetry rig
« Reply #1 on: November 11, 2020, 02:53:06 PM »
Hello,

it's hard to say, from the picture you are posting. However yes, the photographs should overlap more than a bit one with the other, for Metashape (or any photogrammetry application) to be able to align.

You should have two adjacent cameras overlap by possibly 40/50% of the image. Try not go below 30% of overlap.

If you don't have enough cameras to complete the full cylinder with your favourite radius, try enlarging the radius so that each camera shoots a bigger portion of the subject, since you can't unzoom.

50mm is quite long focal length, for instance my scanner has 1.3 meters of radius and I use 24mm fl in order to cover the people in an optimal way. With 50mm you need a much larger radius than what I have.

cheers


James

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Re: Issue with Alignment in Photogrammetry rig
« Reply #2 on: November 11, 2020, 05:32:55 PM »
Guessing from the file naming convention that you are using 6 columns of 10 images? Regardless of the size of the room I think 60 degrees between images is going to be too much for Metashape to understand.

My suggestion would be to try 12 columns of 5 images, or 15 columns of 4 images, even if it means you can only cover the top half of the body. (you can then tweak the configuration once you have a working alignment!)

Also you might as well turn the cameras to portrait orientation to get more of the subject and less of the background in each shot.

If that helps, then maybe try rearranging cameras so you have a bit more density around the head/face or wherever you need it.

I'd say it's better to start with a well aligned set which you can then tweak to get what you want (because when it stops aligning you'll know what you did that caused that) than a non-aligned set where you have nothing and no idea what to tweak to get what you want.