Author Topic: Photogrammetry for Miniatures  (Read 271 times)

Offline MarcoSkoll

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Photogrammetry for Miniatures
« on: February 11, 2021, 02:57:43 AM »
"What is photogrammetry?"

Photogrammetry - or more specifically, "stereophotogrammetry" - is a process where a computer uses images of an object from multiple camera angles in order to calculate the three-dimensional shape of that object.

It does this by finding matching details in the images, and calculating how they move from one image to the next, working out the depths of these points in three-dimensional space based on that. From this, it can then create a 3D geometry of the object.

In short, give a computer enough pictures and it can do some complicated maths to create a digital copy of that object.

In this case, our objective is to scan in miniatures for the purpose of virtual gaming. Here's some I made earlier. (Cue Blue Peter theme).



What you will need
This first part of the guide will address the actual photography process, and I will be adding to this guide shortly on the photogrammetry process and preparation for Tabletop Simulator.

To start with:
- A miniature (duh).

- A camera that can take good sharp photographs of miniatures

- A clean, plain backdrop, ideally in a light grey.

- 3DF Zephyr Free. https://www.3dflow.net/3df-zephyr-free/

- A computer that can run Zephyr.

Zephyr is unfortunately Windows only (but there are free alternatives when it comes to photogrammetry softwares for Mac and Linux, and the photography methods should apply as well to these). It also ideally benefits from a powerful NVidia graphics card, but this is not mandatory. I have successfully run it on a laptop with a low-end eight-year old processor and no dedicated GPU, and while fairly slow, it was successful.

- Blender

Blender is used for the cleaning up process; Zephyr provides very high quality 3D meshes, but these are too dense for Tabletop Simulator to handle, so we need to prepare them for the actual gaming.
Blender is some what technical, so I will be doing a full video guide for this part of the process.

(Don't worry if you're not hugely technically minded; I will be offering to do a reasonable amount of model clean-up for people I'm doing virtual games with. Just don't ask me five minutes beforehand).


~~~~~

Creating a data set (or "Photographing the miniature lots").

3DF Zephyr's free edition is limited to 50 photos, but this is entirely sufficient for our purposes (and even to some extent encourages us to not spend too long taking an unnecessarily large number of photos).

Before you start:
This is very important, so I'm going to put it in big letters:

Make sure the model is actually ready for photography.

You're about to spend the time to take a lot of photos, and if you notice afterwards that the model is dusty, has a spot of worn paint, etc, you'll end up having to start over. Check the model thoroughly first, or expect to do the whole thing again after you notice that mistake you didn't spot earlier...
(I am speaking from experience).

Setting up:
The photogrammetry process obviously benefits from clear sharp photos, so you want to set up to take the best pictures you can.

This is what my set up looks like. You don't have to have something this elaborate (a lot of people do very good photogrammetry with smartphone cameras), but if you do have access to this sort of thing, take advantage.



We're outside for good lighting, but the set-up is actually angled away from the sun; good lighting is important, but even lighting will result in the most faithful reproduction of the figure, so the diffuse reflected light is better than harsh direct lighting.

As another point on lighting, I've used a grey backdrop. Although it reflects less light back onto the model, it won't bloom and overexpose in the camera, so it won't overwhelm the model in the photos.

And I'm also using a tripod, with the camera set on a two second timer. As the camera is rock-steady, I can raise the exposure time to let my use the minimum ISO settings and narrowest aperture for the sharpest and cleanest possible pictures.

Again though, this is not strictly necessary. If you can take decently sharp pictures on a smartphone, then that should be fine. Do the best pictures you reasonably can.

Depending on the quality of your camera screen, it may be advisable to take one or two photos first and then check them on a proper screen; you don't want to find out when you download them that they're all badly over or under exposed.

As far as setting up your camera and miniature, to begin with, you want to keep the whole miniature in shot, and try to keep all photos from as close to the same distance as possible.

Taking the photos:
I started by taking eight photos of the model on the level, at effectively the standard compass points - N, NE, E, SE, and so on. In this case, I used an old plastic tub with some markings to help me keep track of the orientation.



Once that was done, I took additional sets of pictures from (roughly) 22.5, 45 and 67.5 degrees above the level, as well as 22.5 below.

At each level, I took eight pictures - for the 45 degree level, I took them at the same N, NE, E, SE, etc compass orientations, but for the other sets, I took them at angles halfway between (NNE, ENE, ESE, etc) to help provide more varied angles of the model.



This will ultimately result in a set of forty photos.

3DF Zephyr Free will permit photosets of up to 50 photos, so for some of my miniatures (mostly the 54mm ones), I also elected to zoom in as close as I could on the head/upper body and take another eight photos (again, going for the compass angles between the first set) so that the software could best recreate this focal point of the model.

This brought the total to 48 photos. If you've got any particular details you think would benefit from a photo from another angle, then you've got two photos left, but other than that, you should now have a "data set".
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Captain L. Rollin: "Nonsense. Never heard of it."
Birgen: "Pick a window. I'll demonstrate".

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Offline MarcoSkoll

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Re: Photogrammetry for Miniatures
« Reply #1 on: February 11, 2021, 02:58:19 AM »
This is a placeholder post for the guide for 3DF Zephyr.
S.Sgt Silva Birgen: "Good evening, we're here from the Adeptus Defenestratus."
Captain L. Rollin: "Nonsense. Never heard of it."
Birgen: "Pick a window. I'll demonstrate".

GW's =I= articles

Offline MarcoSkoll

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Re: Photogrammetry for Miniatures
« Reply #2 on: February 11, 2021, 02:58:35 AM »
This is a placeholder post for the guide for Blender.
S.Sgt Silva Birgen: "Good evening, we're here from the Adeptus Defenestratus."
Captain L. Rollin: "Nonsense. Never heard of it."
Birgen: "Pick a window. I'll demonstrate".

GW's =I= articles

Offline MarcoSkoll

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Re: Photogrammetry for Miniatures
« Reply #3 on: February 11, 2021, 02:59:18 AM »
This is a placeholder post for the guide for importing the models into Tabletop Simulator.
S.Sgt Silva Birgen: "Good evening, we're here from the Adeptus Defenestratus."
Captain L. Rollin: "Nonsense. Never heard of it."
Birgen: "Pick a window. I'll demonstrate".

GW's =I= articles

Offline MarcoSkoll

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Re: Photogrammetry for Miniatures
« Reply #4 on: February 11, 2021, 03:03:42 AM »
Hi all - you'll notice that the guide isn't exactly complete yet, but I am working on it.

I'm still fighting the effects of tendonitis, so my capacity to do large amounts of writing is intermittent.

The inital photography is one of the most important (and time consuming) parts of the process, and as some people may be dependent on daylight/weather, getting that part up gives them a headstart while I'm getting the rest of the guide finished.

(Also, it gives me a kick in the butt to get the rest written up).
S.Sgt Silva Birgen: "Good evening, we're here from the Adeptus Defenestratus."
Captain L. Rollin: "Nonsense. Never heard of it."
Birgen: "Pick a window. I'll demonstrate".

GW's =I= articles

Offline MoeGee

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Re: Photogrammetry for Miniatures
« Reply #5 on: February 16, 2021, 05:29:58 PM »
Sweet. I'm gonna try this out next weekend and will post the results.
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