Boolean ops and a few other questions

[coldby]

- Any hint about how to use the boolean operations (tool menu)? The manual seems to ignore all of them, unless the related info is extremely well concealed.

- Does AC3D distinguish between a solid object and a closed shell?

- How do you split a surface in more than two connected sub-surfaces (i.e. adding a vertex inside)?

Thanks and sorry if my questions are trivial - being a newby is awkward but fortunately doesn't last long

[Dennis]

You can find guidance on the Boolean plugin in the "Help -> About plugins..." menu item. Select the "CSG plugin" item and docs will show up in the bottom window.

It would be nice to get these in the manual as well, though...

The Boolean (CSG) plugin does recognize solid geometry, but, in general, AC3D is a polygonal modeler that does not care about solid/shell geometry.

Not sure about the third question? Does "Surface -> Divide" do what you want?

Dennis

[coldby]

- Thanks Dennis, I'll read the help too.

- Your second answer forces an obvious question: how do I turn a shell to a solid obkect in order to use it in boolean operations? Can I do that at all?

- I tried 'surface/divide', but apparently the new vertices get always placed on the pre-existing sides. What if I want to put a new vertex in the middle and then split the surface by 'radii' connecting it to the existing vertices? The goal is to increase the detail only where it's needed leaving the rest as simple as possible.

Thanks for your patience (provided that I didn't use up all of it)

[Dennis]

Originally Posted by coldby

- Your second answer forces an obvious question: how do I turn a shell to a solid obkect in order to use it in boolean operations? Can I do that at all?

For the Boolean to work, all you need to do for best results is make sure the surfaces of your object face "out" from the center of the object. If you make all the surfaces in your object 1-sided, you can see which way the surface faces (or, turn on the Normals in the view window) --- if they're all facing outward, creating a closed/defined volume, you should be ok.

I can't vouch for how well the Boolean tool will work if the object isn't "closed" (i.e., a cube with one side missing) --- it tends to work fairly well in tests I've done, but I'm not sure if there are limitations here or not.

Originally Posted by coldby

- I tried 'surface/divide', but apparently the new vertices get always placed on the pre-existing sides. What if I want to put a new vertex in the middle and then split the surface by 'radii' connecting it to the existing vertices? The goal is to increase the detail only where it's needed leaving the rest as simple as possible.

I see what you mean. I know of no standard tool in AC3D for doing this. You could perform a Surface -> Divide and then combine/split surfaces from the center vertex, I suppose, then delete the unused vertices --- maybe there's a better way? If the surface has more than 3 sides, you could do a Surface -> Triangulate, then insert a vertex on one of the trinagle lines going through the center of the polygon, then combine/split surfaces as needed. There may be much better solutions depending on the specifics of what you need, though...

[Andy]

I see what you mean. I know of no standard tool in AC3D for doing this. You could perform a Surface -> Divide and then combine/split surfaces from the center vertex, I suppose, then delete the unused vertices --- maybe there's a better way?

Use Surface->Spike and set the size to 0.

Andy

[Dennis]

Originally Posted by Andy

Use Surface->Spike and set the size to 0.

Andy

Figures the lead developer of the software would have a better answer

[coldby]

Andy, you're a genius!

[coldby]

OK Dennis, I finally tried to ask the Help about how to handle boolean operations... and all I got was the opportunity to read the manual once more
Am I missing something obvious?

[Dennis]

Did you read the About Plugins section for the Boolean operation? That gives a very good description of how to use the tool. Have you done any experiments with it? That's often the best way to learn.

Below are some visual examples of how it works. In all of the examples, there is a Sphere that slightly overlaps a Cube. When a boolean operation was performed, the Cube is set as "A" and the sphere is "B". The "Delete" checkbox is checked on both A and B.

In the top image below, there are 4 shapes. In clockwise order from the the top left, they are:

1. Union of A and B
2. Subtract A minus B
3. Subtract B minus A
4. Intersection of A and B

The bottom image is the same, but I included wireframes showing where the original objects were before they were deleted.

Try experimenting with this.

HTH

[coldby]

Thanks Dennis, that's exactly what I was expecting of it - more or less the way Bryce handles the matter. Hope you won't mind me asking another few questions after playing with it for a while.
You''re right, there's no better way than experimenting and cursing until you find your own way out - however the measly hints normally provided by manuals help a lot - once you find them




"If anything else fails, try reading the manual" (R. Bloch, Murphy's law)