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3D Model of my Athenian Tetradrachm


Kaleun96

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Last year I briefly dabbled in using photogrammetry to create 3D models of my coins but couldn't quite get results I was happy with. Recently, another collector has been sharing his results on reddit and with some help from him I managed to create a model of one of my Athenian tetradrachms.

You can view the 3D model herehttps://sketchfab.com/3d-models/athens-owl-tetradrachm-d5e9a7d0f89c4be697d99446222b1368
It's best viewed from a desktop computer as you can then hold down the alt key while dragging with your mouse to change the angle of the light and see the coin illuminated from a different perspective. It may also take a little bit to load all the textures depending on your internet connection.

Due to the need to use cross-polarised light to be able to create accurate models without any "baked in" reflections, the appearance of silver coins is never quite right so it does look a fair bit different here to how it would in the hand but it's just the trade-off you have to live with when doing photogrammetry.

For fun, I also 3D printed the model at 5x life-size and gave it a quick coat of Old Cabinet Toning™️😁

20230730_163232.jpg.5e2325d07feb6a8df75dc0a142607181.jpg

20230730_163214.jpg.ae0149d68b302595e8efcdf9892b877b.jpg

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58 minutes ago, Kaleun96 said:

Last year I briefly dabbled in using photogrammetry to create 3D models of my coins but couldn't quite get results I was happy with. Recently, another collector has been sharing his results on reddit and with some help from him I managed to create a model of one of my Athenian tetradrachms.

You can view the 3D model herehttps://sketchfab.com/3d-models/athens-owl-tetradrachm-d5e9a7d0f89c4be697d99446222b1368
It's best viewed from a desktop computer as you can then hold down the alt key while dragging with your mouse to change the angle of the light and see the coin illuminated from a different perspective. It may also take a little bit to load all the textures depending on your internet connection.

Due to the need to use cross-polarised light to be able to create accurate models without any "baked in" reflections, the appearance of silver coins is never quite right so it does look a fair bit different here to how it would in the hand but it's just the trade-off you have to live with when doing photogrammetry.

For fun, I also 3D printed the model at 5x life-size and gave it a quick coat of Old Cabinet Toning™️😁

20230730_163232.jpg.5e2325d07feb6a8df75dc0a142607181.jpg

20230730_163214.jpg.ae0149d68b302595e8efcdf9892b877b.jpg

Fantastic 3D imagery. I took the liberty of a screenshot, having never held an example of such I was amazed at the incuse depth on the reverse. Incredible

 

Capture3D.JPG

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Very interesting! Yours is definitely the best model I've seen so far. 

The biggest hang up I've seen, which you've solved, is getting rid of whatever held the coin up. I assume you took a number of photos on a turntable, created the model in Metashape, and then exported it to Sketchfab. However, to get the coin to stand up I believe you would have had to put some gum or something there, but it's completely removed from the coin.

Did you rotate the coin and take a second set, then used the two sets of photos to remove the base in Metashape?

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24 minutes ago, kirispupis said:

Very interesting! Yours is definitely the best model I've seen so far. 

The biggest hang up I've seen, which you've solved, is getting rid of whatever held the coin up. I assume you took a number of photos on a turntable, created the model in Metashape, and then exported it to Sketchfab. However, to get the coin to stand up I believe you would have had to put some gum or something there, but it's completely removed from the coin.

Did you rotate the coin and take a second set, then used the two sets of photos to remove the base in Metashape?

Thanks! And yeah that's exactly the issue I had been dealing with when I first tried this last year. I've tried using blu-tac etc to hold a coin up before but you always risk the coin shifting slightly, and it does tend to shift ever so slightly, which makes alignment harder. Instead I decided to support it at both ends, which also allows me to photograph it horizontally, as my normal camera setup has the camera mounted vertically to shoot a coin laying flat. See some pics below of my little half-3D printed / half SmallRig camera parts contraption I made to rotate the coin.

As you guessed, I had to do two passes of the coin, each with the coin held at different points. The first pass I did 36 positions, so one focus stack every 10 degrees. Each focus stack was between 5-16 pictures depending on the angle of the coin. For the second set, which was mainly to get photos of the previously covered edges where it was held for the first stack, I just did 18 photos at 20 degree increments. Then Metashape takes care of the rest!

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20230725_214123(2).jpg.9453abc97a9aacc8162dd98ac5dedfc7.jpg

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15 minutes ago, Greekcoin21 said:

How very interesting, will 3D copies of unobtainable coins become collectible ?.

Seems possible in this day and age of NFTs, though they seem to have passed their peak phase at least for now. One concern I think is whether people could use the models to make forgeries. I don't think a regular FDM 3D printer, like the one I used, would be suited for this but it's possible resin SLA printers could print a mould in fine enough detail. The forger might just have to go through a few steps of going between negative and positive copies to end up with something in the right material before casting a coin or perhaps even a die.

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On 7/30/2023 at 7:43 AM, Kaleun96 said:

Recently, another collector has been sharing his results on reddit and with some help from him I managed to create a model of one of my Athenian tetradrachms.

That is amazing. Just think how much has changed in recent years. Not long ago that sort of 3-D image creation with manipulation capabilities would have been unimaginable for a private person, and a major project for a corporation. Your coin and image are both beautiful and impressive. 

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7 hours ago, Valentinian said:

That is amazing. Just think how much has changed in recent years. Not long ago that sort of 3-D image creation with manipulation capabilities would have been unimaginable for a private person, and a major project for a corporation. Your coin and image are both beautiful and impressive. 

Thanks! Yeah this kind of thing has rapidly grown over the past 10 years or so and now we're at a place where even people with a cellphone could probably achieve quite decent results.

Would be great to work with a museum or similar on digitising some of their collection this way. The current limitation is the time it takes to shoot all the photos. I'm working on something that will attempt to automate this part based on a few measurements of the coin's geometry but it may be a few months before I get around to finishing it.

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