3D scan of coin using photogrammetry

[Bert Van Kets]

Hi all,

I want to make duplicates of a medieval coin (time period of Charles The Great). I have the confirmation of the museum I can have access to the coin but only on location.

I'd like to use photogrammetry to make the 3D scan. Making the pictures is not a big problem. I am wondering about a few things though.

1. Do the images need to be in focus from front to back? If so I have to use focus stacking and that's a lot of work.

2. What is the best open source photogrammetry software for this at the moment? Meshroom? I have Windows and Linux at my disposal.

3. What open source software do I use to do the cleanup? Blender? Meshmixer? I don't know any of these apps but am eager to learn.

Thanks for any input.

Bert 

[TobyCWood]

Number one thing is lighting. It must be flat and consistent around the entire item. If not then your best bet is a turntable with a blank background. Yes you need to be in focus for the depth of field.

Best SW is Agisoft Photoscan.

Blender or 3D Coat for cleanup.

Like 3D Printing, 3D capture is not a one project thing. That is, expecting to use it once for one project will be tricky. There's skills that need to be acquired and used repeatedly to get an optimal result.

I suggest a good DSLR(i.e., not a point and shoot camera), some photography skill, some time with Photoscan and your mesh cleanup tool of choice be it Blender or 3DCoat or Meshmixer.
or... you could just wing it with something that works on your smartphone.

[TobyCWood]

It looks like Agisoft changed the name from Photoscan to Metashape. You can try it in demo mode for 30 days. You do not need the Pro version.

[Juan Posada]

You also will want a fixed focal length lens rather than a zoom. 50mm worked well for me when I tried this technique. Eventually I caved and bought a structured light system.

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[Peter Cameron]

Alternatively, you could use photo stacking software like Helicon, which has a 3D export option (.OBJ). I assume they use the depth map used in the stacking process as 3D data, but this should be sufficient since a coin is shallow. My only worry would be that the rim is at 90 degrees to the focal plane. Without doing some tests, I'm not sure how it would resolve. The downside would be that you would have to join the 'head' and 'tail' meshes using something like Meshmixer. 

The upside is that it would be much easier to set up as the camera has to move along one axis only. This means you can concentrate on resolution and focal depth and still have fewer images to process.

Cheers

peterC

[Owen Collins]

I use Metashape and do think it is a great solution for photogrammetry. In the new versions you would need the Pro license to do any manual adding and editing of reference points across photos. 

Sent from my mobile device 

On Aug 31, 2021, at 6:29 PM, Peter Cameron <pete...@gmail.com> wrote:



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[Bert Van Kets]

Thanks for the info all,

I have students in the house so could purchase an educational standard license for $59.

But if I do want to use open source software, what would be an open source alternative?

I have a decent DSLR (Nikon D5500) and will use focus stacking to create images that are sharp front to back. Lots of work but well worth it I guess. 

I plan to build a little turn table so I can create fixed positions for all different images.

Lighting will be done with 10W LED lights in a small soft box. Should I light at 90 degrees from camera, from all sides (flat light) or from the direction of the camera (ring light)?

Thanks 

Bert

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[Daniel Rosen]

I use Trnio on an iPhone 12 and have great results. Is free and allows download as STL and .obj

[Kurt at VR-FX]

I thought that Meshroom had been mentioned in this thread - but, many it was in another thread recently. So, yes - there is Open-source version - here - check it out:

    https://alicevision.org/#meshroom

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[ekag...@gmail.com]

have a look at the openscan project. that thing can scan a detail on a key. the trick is to have a matt texture on it. baby powder helps.