BoundingCylinder

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 From:  BurrMan
5715.1 
Hi Michael,
I use the BoundingBox alot and would like a BoundingCylinder also. If it's easy enough, maybe we can get that?

Thanks,
Burr
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 From:  Michael Gibson
5715.2 In reply to 5715.1 
Hi Burr, what kind of bounding cylinder do you mean exactly, it's not easy to calculate for example the axis direction for which particular axis orientation will have the minimal sized cylinder.

Or do you mean with a fixed axis direction? Even with a fixed direction finding where to place the axis is not necessarily very easy as well unless you are again talking about some kind of fixed value.

Here's an example of why it's not so straightforward - here are a few objects:




The bounding box around them and its center looks like this:




Maybe you were thinking of having the cylinder centered on that same bounding box center point. But look what that gives you:




This is not the tightest cylinder that can be made, see the extra space in this area here:




To get an actual "smallest radius bounding cylinder" you can't just place the cylinder axis at the bounding box center, a cylinder and a box are pretty different in shape so using bounding box information for the cylinder doesn't reallly give the real result for it (there are corners on a box, but no corners on a circle basically), it's something that needs a completely different kind of calculation.


It is possible to put a cylinder that will contain the bounding box so that you know that the object is totally contained inside the cylinder but it won't be the smallest possible one, and I probably would hesitate to make a special command that kind of implied that it was building the actual smallest bounding cylinder when it was not really doing that at all.


What are you planning on using the cylinder for?

- Michael

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 From:  BurrMan
5715.3 In reply to 5715.2 
Hi Michael,
It would be used in conjunction with a CAM program for stock setup. The cam program has this option too. It does a cylindrical bounds with the option to use either the x, y or z as the axis direction. it DOES do the tightest cylinder on the presented object, which gives me it's bounds center point.

i would be looking to get this for doing 4th/5th axis work using cylindrical stock.

I think the cylinder would just be looking for the largest axis of the boundingbox output, if using the "x" as a default axis, then that would be either a Y or a Z value, and so on.

I can make a quick demo of what it looks like if that will help.
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 From:  BurrMan
5715.4 In reply to 5715.3 
Hi Michael,
I just did a few tests. It is inded different than bounding box. The operatation should produce a cylinder which just fits the largest points of an object, no mater it's shape or how it's rotated. The operation I'm familiar with has an option to set an X, Y or Z as the calculation axis for any given object. Maybe this is a mass calc we dont have yet?
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 From:  Michael Gibson
5715.5 In reply to 5715.4 
Hi Burr,

> I just did a few tests. It is inded different than bounding box. <....>

So yeah that's not at all easy to compute, it's not really related to the bounding box, but an entirely separate calculation.


> Maybe this is a mass calc we dont have yet?

Yeah I guess something like a "projected centroid" type thing, I took a quick look around and I do not see any functionality that seems to resemble that in Solids++ so that would likely be a significant project to try and implement that, sorry.

- Michael
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