Faceting Help

[fiveD]

Hello, I'm new to Stella4D and learning how to use it.

I'm struggling with how to perform faceting and hoping someone can share some screenshots or a video to demo how this function can be used.

I'd like to create something similar to the object I spotted on X (twitter) which I think uses faceting?

https://x.com/AlbertPCarpent1/status/17 ... 5309473944



Thanks for any help.

[robertw]

You need a combination of techniques, including faceting, to create a model like that.

These pages may have some relevant info:
https://www.software3d.com/TopoSHI.php
https://www.software3d.com/TuteSpherical.php

For the image you include, the steps would be something like this:

1. I'm going to start with a Stella Octangula. Looks like they used a more spiky version, but you can start with whatever you like. I loaded the "Tetrahedra 2" from Stella library -> Compounds.

2. Use "Poly->Subdivide Faces" and choose 10 as the number of subdivisions. Display edges so you can see what happened. You may experiment with values other than 10, but I just went with 10 as it looked like what they used in that model.



3. I recommend keeping the original model on the left, and changing the view on the right to the Faceting Preview view. You may also want to lock the orientation of the two views to keep them in sync.



4. Make sure "Options->Maintain Reflexibility" is NOT enabled.



5. Enable Faceting Mode.



6. Now you can use Shift-Left-click on the new vertices to draw whatever shape you want on the faces. Here's the start of me roughly copying the original model.



7. Once you've started on part that's symmetrical with where you started, you can just hit "." to complete the shape.



8. Hit the tick button, or Enter, to accept the new facet you've drawn. You may want to turn edges off now to see the shape more clearly in the Faceting Preview window.



9. At this point you can also look at the unfolded nets and the new facets will appear there, and you can print them out.

10. Note though, if you do this with a compound, then the parts of the compound will no longer have any connection to hold them in place!

11. This model is still in an unfinished state. The green edges indicate edges where a face still needs another matching face to make a proper polyhedron, and you won't be able to turn this into the new base model as it is. To do that requires some extra steps BEFORE starting the faceting, as follows.

12. Need to put the original subdivided model into a memory slot, using "Edit->Put Model in Memory->Memory 1" or typing "m1". Then change the scale of the model slightly using "Scale->Base Polyhedron Radius" or something else from the Scale menu. Then add the two different sized models together again using "Edit->Add/Blend from Memory->Memory 1". Choose NOT to blend coplanar faces back together. For this example, I used base radius of 8 and 7.5.

13. You can use Ctrl+Shift+Left-drag to explode the faces apart and see the second layer of faces inside. Use Ctrl+Shift+Right-click to snap the faces back together.

14. Now draw the facet you want on the outer model. Need to be a bit more careful now to make sure that edges meet properly. If you draw a short edge which will meet a long edge, Stella won't recognise them as connected. You may need to include an extra vertex along the long edge to help with this.

15. Draw the same facet again on the smaller model. Can be a bit hard to access the inner surface. You can explode the faces apart, or hide the outer faces.

16. Next part's a little more tedious. You need to create facets to connect the two facets you already made. But generally doesn't take long, especially since Stella is creating all the symmetric repeats for you. Seen below with one facet left to draw.



17. Finally there shouldn't be any edges left hightlighted in green or other colours. You can hit the left-and-down button near the top right of the Faceting Preview window to make this the new base model. Here's what I got.

[fiveD]

Hello Robert - thanks for your detailed reply. I'm following your steps but seem to be getting caught at steps 6 & 7.

I've tried several times to draw the shape on the faces but cannot replicate this example. I get this outcome in the screenshot.

Please can you clarify steps 6 & 7? The result seems to rely on where you start and end the vertex clicking.

Thanks.

[robertw]

At step 6, here's an image which shows what order I clicked on the points. You can start anywhere in the cycle, but this is one example.

The reason for including points 4 and 11 is to break up long edge 3-5 which will meet with a short edge like 2-3, so that edges of the same length meet.

We haven't completed the whole cycle here, so it looks a bit weird, but hit "." and the pattern will be auto-repeated to complete the cycle for you. You can actually hit "." after point 9. Does something unexpected if you try after 8.

[fiveD]

Thanks Robert - I managed to do it now It would be great if you could "paint" the facets using polygons to make it easier.

Would you please be able to show a similar screenshot as your last with the numbers for faceting either a dodecahedron or icosahedron?

Thanks.

[robertw]

A dodecahedron and icosahedron are convex, so there's no other faces to avoid, but you could still draw whatever patterns you wanted on there. Will leave that as an exercise.

You can kind of paint with the existing triangles instead, rather than drawing new larger polygons. Use Ctrl+Right-click on any triangle to use it as a new facet.

[fiveD]

Thanks Robert. I did see the CTRL right-click function, but is there a way to multiple select triangles using this function?

[robertw]

Just Ctrl+Right-click on each triangle you want to add as a facet. Not sure what you mean about multi-select since you can already add as many as you want one by one. I guess it could be nice to be able to hold the mouse button down and drag across multiple triangles, which you can't do at the moment, but not much of a saving.

[fiveD]

Hello Robert, I am doing this, but when I Ctrl+Right-click the next triangle, it deselects the previously selected triangle and then selects the currently clicked triangle. It does not seem to accumulate i.e. multiple triangles turning white as each one is Ctrl+Right-clicked. Unless I am missing something here....

[robertw]

You should have the base view open on the left, and the Faceting Preview view on the right. Ctrl+Right-click on a face in the base view will add it as a facet in the Faceting Preview view. They should accumulate.

Maybe you're using Ctrl+Left-click rather than Right click? That would just select the face without creating a facet from it.

[fiveD]

Hi Robert, I wanted to revive this post.

I imagine you are busy but I'd really appreciate it if you could knock up a video to demonstrate faceting a bit more. I want to experiment further with other shapes but struggling with the process. A video with narration would really help to get a better understanding. Would you be able to please?

Here's another example of a faceted shape, but wouldn't know where to start.

https://x.com/AlbertPCarpent1/status/17 ... 2817195501

Thanks, David

[robertw]

Hi David,

To be honest, I'm far less likely to find time to put a video together. And if I made a video about the original shape you asked about, it still might not help you with other shapes like the new one you mentioned.

Were you able to make the original shape?

There's no specific answer for the first step, which is making the initial shape which you can then subdivide. That's going to depend on the shape. The new one doesn't appear to be any particular well-known shape. Looks like maybe they started with a cuboctahedron, added it a memory slot for later, then augmented the faces with pyramids (Poly->Augment Polyhedron) and use Ctrl+Left-drag during the augmentation preview to make the spikes bigger. Repeat for both face types. But the final model also still has pieces of the original cuboctahedron faces too, so add that back from the memory slot we put it in. Then subdivide the faces at level 5 and facet like before.