Simple Boolean Addition — why does it fail?

[enkidu_jones]

Hi all, I've been using Cheetah3D for many years and currently have version 8.1.3. I have also long had issues with Boolean operations just not working, and today I have a simple example where I'm trying to add three capsules together in a boolean operation. I can add two of them, but when I try and add the third Cheetah3D beeps and the capsule disappears.

How to reproduce this issue? Take the attached file and add a Boolean creator, set its operation to "Addition", then drag on "Capsule" and "Capsule.1" — all fine. Now try and drag on "Capsule.2" — when I do this Cheetah3D beeps and "Capsule.2" disappears.

Any help would be much appreciated, thanks!

 

[frank beckmann]

Works here. Perhaps you used the Modifier/Creator in the wrong order. File attached: middle=raw set, left=editable mesh (questionable topology due used objects, right=simpler topology due cylinder.)

 

[Helmut]

Note that you get the same result with a single capsule and 2 bends of 90°. This may even reflect the manufacturing process if the item (a metal rod) is bent twice when at a high temperature. In the Boolean addition you get a sharp crease which may be problematic (bacterial and fungal growth) for items used in a sanitary environment.

 

[enkidu_jones]

Thanks all. I found the second vertical capsule appeared if I moved it down by any amount, so I just did it by 0.01 and all was okay.

I notice in frank's examples (and thank you for going to that trouble) that the boolean has been added as a child to one of the capsules. Does this imply that simply adding more than two child objects to a boolean is incorrect? If I take the Boolean out of the parent capsule it isn't visible at all — which again makes no sense to me. The example also makes me wonder what the point of an addition boolean is, if I can just make objects children of other objects and achieve the same result without the problems of disappearing boolean elements?

It does feel quite counterintuitive that I cannot simply drag default polygon objects into a boolean and it perform the set function of subtraction / addition / intersection. This did work in DKBTrace (showing my age there!!!).

 

[gsb]

Thanks all. I found the second vertical capsule appeared if I moved it down by any amount, so I just did it by 0.01 and all was okay.

I notice in frank's examples (and thank you for going to that trouble) that the boolean has been added as a child to one of the capsules. Does this imply that simply adding more than two child objects to a boolean is incorrect? If I take the Boolean out of the parent capsule it isn't visible at all — which again makes no sense to me. The example also makes me wonder what the point of an addition boolean is, if I can just make objects children of other objects and achieve the same result without the problems of disappearing boolean elements?

It does feel quite counterintuitive that I cannot simply drag default polygon objects into a boolean and it perform the set function of subtraction / addition / intersection. This did work in DKBTrace (showing my age there!!!).

Hello,

Frank’s comment demonstrates the observation that you have made the boolean addition process more problematic by using a capsule, rather than a cylinder for the horizontal piece. The minor tweak you found necessary to perform in order to get the pieces to show properly was made necessary by the presence of a fair amount of surface of the ends of the two vertical capsules that occupy the same space as the horizontal capsule ends.

Frank demonstrated that by using a cylinder of 10 units shorter in place of the horizontal capsule, the problematic geometry does not exist.

Thinking about how an object might be fabricated and then used in reality is helpful, if not best, when working with 3D modeling.

Both Frank and Helmut’s comments are based on that foundational tidbit.

Frank’s real-word example would be fabricating your desired object from three pieces of tubing or rod.

Helmut’s suggestion was to use the real-world example of bending a single piece of tubing or rod.

One would choose between those two fabrication techniques based on the intended use of the object as well as the mastery of available tools.

IF you are wanting the object you are trying to make, to be a single piece of geometry that looks like it was fabricated by cutting and welding tubing or rod, then using a boolean might be a reasonable way to start.

IF you are trying to make a single piece of geometry that looks like bent tubing or rod, then bending it might be best.

IF you are simply wanting the three pieces you have created to _look_ like they are one object, and you don’t need them to be a single piece of geometry, that is where you could make the two vertical capsules children of the horizontal piece and not bother with creating a single piece of geometry at all. Not really different than the example file you posted except that moving the parent would also move the children.

The current boolean tools do a pretty good job of adding, subtracting, and intersecting objects. Simply. Where any boolean tool is going to have a problem is trying to work with objects that have surfaces that occupy the same space.

Hope this helps.

Cheers,
gsb

 

[Helmut]

The Boolean operation removes specific parts of the geometry of interpenetrating meshes and generates a "combined" surface. It produces a new object, depending on mode (addition, etc).
In your example, there are 2 critical areas where the geometry of the capsules to be added occupy the same space, this being the quarter-spheres where the capsules - positioned at an angle of 90° - terminate and overlap.
If you analyse Frank B´s solutions in wiremode you will see the different meshes generated by the Booleans when
1 capsule + capsule + capsule
2 capsule + cylinder + capsule
are used. The geometry in the interpenetrating parts is messy in sample 1 and clean in sample 2 after addition has been deployed.

If curious, please read up on Boolean carving algorithms (often referred to as mesh Boolean operations or CSG—Constructive Solid Geometry).

 

[frank beckmann]

Does this imply that simply adding more than two child objects to a boolean is incorrect? If I take the Boolean out of the parent capsule it isn't visible at all — which again makes no sense to me. The example also makes me wonder what the point of an addition boolean is, if I can just make objects children of other objects and achieve the same result without the problems of disappearing boolean elements?

Perhaps you should take another closer look at the Boolean modifier and the Boolean creator and the difference between Modifiers and Creators in general and destructive versus non-destructive modeling. You can find this file from the screenshot under Help->Cheetah3D samples->Modeling. And there are also Booleans in the polygon tools, but they only ever work with two objects at a time and better with editable meshes.