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Old 22nd July 2004, 01:30 AM   #1
Stiglr
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Default Getting it straight about Booleans

This feature is frustrating in the extreme and I just can't figure out how to get the results I want.

OK: Let's say I have an aircraft fuselage shape, and I need to cut out a few banks of windows. So, I create a poly shape in the shape of the window, extrude it to intersect the fuselage at a right angle (across x axis), so as to simultaneously cut the window on both sides in the same parallel position.

Then, I enter Boolean, select the window shape as A, the fuselage as B, use the check box to select the A window shape to be Deleted (as I don't need it after it's gone) and select Subtraction B-A.

Logic tells me that after I complete this, the fuselage shape only should remain with two window shaped holes on either side (and completely through the fuselage if it's solid and not hollow.

This doesn't happen. The window shape remains, and often a totally new fuselage remains in the exact position. I've sometimes found that the shape I actually want, called CSG0 or some such, is actually there, but it's hidden by the original fuselage shape, which can't be detected since they are exactly sharing the same space.

That makes no sense. Should i select the fuselage to be Deleted as well?

I'm kind of at sea here, and want to learn how to do this in one quick and easy trip throught the Boolean section without headaches.

===========================
On a similar note, it might be really nice to be able to select an item you want to display as Only Selected from a list of objects in the file. That way, if you want to check your Model Info and find out what some object is named 'cylinder' that you're not sure what it is, and forgot to name the object while you were creating it, you could quickly find out. It would also help you sort out CSG0's from extraaneous fuselages in the above case.



Still, though, I love this product.
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Old 22nd July 2004, 02:49 AM   #2
Andy
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Email me your model and I'll take a look.

I'm not sure exactly what you mean by your second point. You can use Tools->hierarchy to see what's named and selected.

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Old 22nd July 2004, 11:46 AM   #3
Stiglr
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The Heirarchy tool tip certainly worked; didn't know about that one! Thanks, it solved that problem, at least.

As for the original problem, I figured it out. I simplified things by taking just a fuselage section into a completely new file, so I could be sure how many objects there were or weren't.

The problem is, the original B operand, the fuselage, remains, intact, after the cut is made in this scenario. This should be changed though: if you're cutting A out of B, an uncut version of B should not be hanging around after the operation, in the exact same physical position, and having the same material color: what becomes CSG0 is what should be left, no matter whether it retains the original name of the object or not. Do you see how this can seemingly result in "nothing happened"? That's exactly how it "appears". It's confusing.

Anyway: the solution is to check BOTH operands for deletion, and the result is GSG0 after the operation, the properly cut piece. You can rename that fuselage and continue happily with your work. But selecting this arrangement in the Boolean dialog, to me, seems like I'm saying, "cut part A out of part B, and then delete both objects, leaving absolutely nothing", when what I want to do is "cut part A out of part B, leaving a part B with a hole in it".

Another day, two more lessons learned.
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