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Object Subtract Weirdness
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Object Subtract Weirdness // New Users
Post by johnhoward // Jul 11, 2008, 4:15pm
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johnhoward
Total Posts: 231
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I have a flattened cube and would like to subtract a hole of unusual shape (colored violet in photo 1).
When I do so, the correct shape is there (I think), but most surfaces are invisible. Different surfaces become visable depending on angle of view (photos 2 & 3). Moving back to workspace doesn't help (photo 4).
I don't know whether I'm doing something wrong or if TS 7.51 has a bug here. Any clues?
Thanks. |
Post by TomG // Jul 11, 2008, 4:50pm
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TomG
Total Posts: 3397
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This is why booleans are known as evil :)
The shape you have subtracted is leaving a vast "n-gon" in your original flattened cube. The top face of that cube now has a lot of vertices defining it, when render engines like 3 vertices (for triangles) or 4 (for quads).
When you get an n-gon (ie a polygon with "n" edges for a large-ish number) things can start to go wrong. tS is more forgiving than most and handles faces with holes and many edges quite well, but even then sometimes it goes wrong, which looks like the case here.
This is why people say booleans are a bad modeling tool and should be avoided where possible.
Solutions are many. Quad divide the flattened cube, probably 2 or 3 times, before doing the boolean (ensure "Delete Edges" is NOT checked so that those extra edges are maintained). Or you could point edit and manually try joining vertices that surround the hole to the outer edge that defines the shape after the boolean (so draw a line out from a vertex on the hole to the outer edge).
The boolean could have gone wrong too, so you may need to try adjusting the settings in there.
HTH!
Tom |
Post by Dragneye // Jul 11, 2008, 5:34pm
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Dragneye
Total Posts: 602
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Was just going to start a thread with the same relative question! Ahh, timing.
So... maybe if you 'flip faces' it'll come out viewable?
QUE: what's the procedure/etiquette? I wanted to show a pic of my 2 object mess that won't Boolean and ask a few related questions, and figure that when people look for guidance here, it's best to try and keep similar questions/examples in as few threads as possible, for the most effective education, but this is johnhoward's thread and don't want to be rude. Start a new thread or post here? |
Post by johnhoward // Jul 13, 2008, 5:36am
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johnhoward
Total Posts: 231
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Thanks TomG,
But, so far, none of your solutions do the trick. I found that I cannot point edit the resulting object. If I try to create a new edge, the first point I click on turns red, and no line will extend from it.
I don't see another way to accomplish this, except to point-edit the whole thing from scratch (lots of time), but does this mean that odd-shaped holes simply cannot be cut through a wall? I have tried to get to the odd-shaped hole by subtracting out a series of simple holes. That sort of works, but requires a lot of time also, depending on the shape. That's quite a failure for architectural modeling.
When you say "adjusting setting in there", I'm not sure what you mean. |
Post by johnhoward // Jul 13, 2008, 5:44am
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johnhoward
Total Posts: 231
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Dragneye,
This isn't 'my' thread, so by all means, join in. I tried your "flip faces" idea. Didn't help. It may be, as TomG suggests, that we are dealing here with evil. |
Post by Jack Edwards // Jul 13, 2008, 7:18am
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Jack Edwards
Total Posts: 4062
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LOL Model side booleans aren't as bad as they are made out to be, but they certainly can be finicky -- the right click option panel is your friend. I've never been a big fan of booleans (as you can tell from my sig :p), usually it makes more cleanup work for later -- especially if the model is targeted for SDS.
Keep in mind, Roman announced new booleans for 7.6. ;) |
Post by TomG // Jul 14, 2008, 2:44am
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TomG
Total Posts: 3397
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Try quad dividing before doing the booleans, perhaps two or three times even. Let me know how that goes - ensure Delete Edges is unchecked.
HTH!
Tom |
Post by spacekdet // Jul 14, 2008, 6:54am
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spacekdet
Total Posts: 1360
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Select just the top and bottom faces of your flattened cube and quad divide as Tom suggested.
No sense adding extra polygons along the sides.
If there is a lot of detail in your 'drill' object then the faces that it's going to be cutting through will also need a lot of geometry (in the form of the quad subdivisions) to ensure an accurate hole.
If one or two hits on the quad icon 'doesn't cut it', try hitting it several more times.
The drill object must be a single object, not anything glued...er, encapsulated. |
Post by johnhoward // Jul 14, 2008, 9:47am
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johnhoward
Total Posts: 231
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Thanks all, for your ideas.
When I do quad divide a couple of clicks and uncheck delete edges, I get a boolian error telling me to relocate (the objects, not me). It doesn't work.
If I leave delete edges, the operation works, but with the same bad results as originally described above.
I find that if I select a single face of the drill object, it won't quad divide.
The drill object is an imported curve and, given its shape, couldn't be simpler. It is not glued or encapsulated. When I quad divide the drill object, the results are bizarre (see photo this message showing 1 and 2 clicks).
I reported earlier that the draw tool would not work on the resulting object. That was in Workspace. In Model, the draw tool does work - but only up to a point. I can never complete a surface and make it wholey visable and there are strange diagonals that can not be selected or deleted.
I have taken to rocking back and forth, chanting "Hurry Roman, Hurry". It seems to be working, but very slowly. |
Post by TomG // Jul 14, 2008, 10:39am
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TomG
Total Posts: 3397
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Well, your original object also has one very large N-gon face. This is why Quad divide fails, and gives quite nasty triangulation.
It is worth avoiding such geometry if you plan on using booleans, or if you plan on exporting to another application (eg game engine, another 3D modeler). trueSpace is very forgiving and correctly renders your original object, but booleans and other applications are not so forgiving!
The solution is a painful one - manually edit the object. Since it's symmetrical, the easiest way is to add lines from one side of the object to the other, connecting up the matched vertices. This will turn the one huge face into a series of quads that booleans will handle better.
I've had to do this for when I plan on exporting a model (eg putting it up for sale on Turbosquid). Automatical triangulation is rarely a good solution, as you can see it tends to just join all vertices up to the center, making lots of thin triangles, that are bad for booleans and rendering also.
Manually joining vertices to give quad and triangles only is the best bet you have here :)
HTH!
Tom |
Post by spacekdet // Jul 14, 2008, 3:29pm
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spacekdet
Total Posts: 1360
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Whoa, nellie, back up a step.
Don't quad divide the drill, just the top and bottom face of the cube that you want to cut the hole in. |
Post by Weevil // Jul 15, 2008, 12:16am
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Weevil
Total Posts: 534
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I'm so lucky this problem hardly ever happens to me. When it does I adjust the position a leeeetle bit, and triangulate both the objects to be on the safe side, get a square, move it so it is NOT in contact with any object, copy the cube, and subtract both the copy and the original from both the objects. You need delete edges on, and when you do that, it'll leave the faces that need triangulating, triangulated.
Then do what's in the above posts |
Post by Jack Edwards // Jul 15, 2008, 12:40am
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Jack Edwards
Total Posts: 4062
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I forgot to mention the reason that I am against booleans in principle:
The real evil in booleans, isn't the boolean tool themselves. It's that it stunts a users growth in learning how to model difficult shapes. It becomes a crutch. |
Post by TomG // Jul 15, 2008, 2:04am
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TomG
Total Posts: 3397
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As space mentions, quad dividing the drill won't make the booleans any better. It's the target that needs quad dividing, so it has more faces, so that the intersections between target and drill have more edges to define them and will result in less n-gons.
If you do want to quad divide the original, dividing up manually as mentioned would be the way to go - but indeed, it wouldn't make any difference to the booleans that I know of.
Other options - cut the objects in half since they are symmetrical. This would leave the hole in one edge of the half-cube, like a bite taken out of a cookie, and may give a better result.
Talking of bites, bite the bullet and remodel :) You could use poly draw to draw new edges into the middle of a face, using the drill as your template, then delete the face, for instance. I'd go for using the mirror tool so I only had to draw one half, and both halves matched.
HTH!
Tom |
Post by Weevil // Jul 15, 2008, 4:19am
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Weevil
Total Posts: 534
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Actually yes, the last tip fixes most problems now you mention it... |
Post by spacekdet // Jul 15, 2008, 4:05pm
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spacekdet
Total Posts: 1360
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You can call it a crutch, I'll call it just another tool.
I'm not throwing away my cordless drill and bits anytime soon just because they make a difficult job easier.
I'm pretty sure that you can pull this off easily just by quad-dividing the relevant surfaces on the target (cube) object.
The drill already looks detailed enough, it should be fine as is.
The problem is that the drill is finely detailed, but you are trying to cut that complex shape through a single polygon (or a pair, really, since there is a top and bottom to the cube). Give the top and bottom a few hits of quad-divide and all should go smoothly and quickly with no backtracking needed. |
Post by Dragneye // Jul 17, 2008, 10:26am
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Dragneye
Total Posts: 602
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My question is this: when u right click the boolean icon.... what the heck do those numbers mean? What do they relate to? The manual wasn't very helpful. Basically I got the impression that they should be lowered in value for Hope that the Boolean will work. But the question remains. What number/values should I pick, and why?
In my Colossus thread, I had a heck of a time getting to boolean the parts together, and ultimately was a waste of time when they finally attached. |
Post by spacekdet // Jul 17, 2008, 4:54pm
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spacekdet
Total Posts: 1360
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Oddly enough and despite their labels, one is actually a "Hope Quotient " spinner (add more if you really hope it works) and the other is the "Quantum Random Geometry Generator/Subtractor Factor". Simply adjust this to randomly affect the outcome, but be warned, observing (http://en.wikipedia.org/wiki/Observer_effect) the results may change them!
In other words..."Beats me!"
I never saw much difference adjusting either of them. |
Post by Dragneye // Jul 17, 2008, 7:36pm
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Dragneye
Total Posts: 602
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Me either. After all this time, I think only once did I adjust the numbers and that made the boolean work... without moving the pieces. |
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