Author Topic: Problem generating complex  (Read 122 times)

mikeymakesit

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Problem generating complex
« on: January 06, 2018, 12:29:07 PM »
Hi there, I'm relatively new to Meshmixer.  I've had some success generating complexes.  I don't know the terminology but I'll do my best to explain where I think I'm repeatedly having trouble.  When I create a face group that only touches 1 set of adjacent triangles I have no trouble.  Every time I try to generate a complex based on face groups where there are multiple sets of adjacent triangles it seems like it fails.  I don't understand why.

If anyone can explain 1) why it doesn't work at all, or 2) what I'm doing wrong, I'd greatly appreciate it!

In this model I've selected all of the figurine.  Notice the selection ends along the steering wheel, as well as along the base of the figure on the cart.  First I create a face group from the selection:



Next I generate complex:



Then I see two loops I can choose from.  Actually double-clicking on one of them selects both automatically.  I don't know if it should select both loops, maybe because they're part of the same face group.



Here you see the black areas where new surfaces will be created.  So far so good I believe:



Here I am ready to split the generated complex:



Finally, here's the split objects.  Unfortunately the figurine has not been split from the cart.  Instead there's the original mesh and a single new one like an interface layer on the steering wheel shaft.  There's no corresponding surface under the seat of the figurine.



Any feedback appreciated.  Again I was expecting the originally selected figurine to be split into its own mesh after generating/splitting the complex but that didn't happen.  Thanks in advance for any advice!
« Last Edit: January 06, 2018, 12:35:28 PM by mikeymakesit »

MagWeb

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Re: Problem generating complex
« Reply #1 on: January 06, 2018, 05:11:20 PM »
Interesting issue pointing to a limitation of MM's complex handling.

Just to explain:
GenerateComplex is a unique approach to define object's regions by allowing something which is considered as a mesh error normally: Non manifold faces.
"Non manifold faces" means that more than two faces share the same edge.
A MM-Complex allows three triangles to share the same edge to build some interior surface to split printing material volumes.

ATM this attempt expects a single interior surface for each complex region.
Well GenerateComplex also handles groups with more than 1 (in your case there are two: At the steering wheel and towards the seat) but SplitComplex is restricted to isolate exterior plus one interior surface only.
As it does that and as it can't decide where to add the intended exterior surface it ends at isolating one of the two non manifold interior surfaces ( at the steering wheel) while keeping the second interior surface (as a mesh error) and the exterior surface stick to the cart... Sorry, this might be something to improve....

What you might do:
A: Instead of double-clicking at a group boundary double-click the group: This will create an offset shell complex (which is a single surface). You can split it off but the object's core will still be part of the rest.
B: You might select the steering wheel's shaft and do a PlaneCut (set to Slice(KeepBoth)) on this selection only and merge the right "cut-surface" to the figurine group after that. Now GenerateComplex with that group ....

I'm just a user as you are. Being no Autodesk employee: I do not know where this road will lead to, nor do I claim to've all stuff got right.

mikeymakesit

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Re: Problem generating complex
« Reply #2 on: January 06, 2018, 07:10:48 PM »
Thanks Mag for the feedback, I appreciate it.    ;D

tysonbrochu

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Re: Problem generating complex
« Reply #3 on: January 10, 2018, 05:57:09 PM »
Hey mikeymakesit,

One of the biggest limitations in Meshmixer's handling of Complexes is, as MagWeb mentioned, that it only handles configurations where there is an "exterior" surface and one or more "interior" surfaces. When generating complexes, we allow generation of one "interior" surface per facegroup boundary. Furthermore, we are expecting that every pair of facegroups meets at at most *one* boundary loop. So if you have FaceGroup A adjacent to FaceGroup B, A and B can only meet at one closed boundary loop. Here's an example:

Here's a torus with two facegroups. Notice how the purple facegroup meets the green facegroup in two places.



If I run Generate Complex, the preview looks seems like it will work:



But actually, when I run Split Complex, I get one giant object and one object leftover. This is because Meshmixer expects there to be only one surface that "splits" the purple group from the green group. It just doesn't handle having two surfaces at the moment.



As a workaround, you could try generating a third facegroup, like so:



Now when you run Generate Complex, you can generate a surface at the Purple-Green boundary, and at the Green-Gold boundary.




Later you could merge the purple and gold boundaries if you like.


Hope this helps!
Tyson


MagWeb

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Re: Problem generating complex
« Reply #4 on: January 11, 2018, 05:50:55 PM »
Thanks Tyson,

that's a nice solution I wasn't aware of.

Splitting such a "two sided" complex donut I found some results were one of the two resulting parts gets flipped faces at former interior surfaces (see green group in image below) while its opposite end and the split off part are fine. Other group or complex configurations (as creating interior complex surfaces on all 3 group borders on the very same object) instead worked fine totally.
I'm just a user as you are. Being no Autodesk employee: I do not know where this road will lead to, nor do I claim to've all stuff got right.

MagWeb

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Re: Problem generating complex
« Reply #5 on: January 12, 2018, 03:28:44 PM »
The flipped faces issue in previous post seems to be related to the direction interior surfaces are created generating the complex object.
The attached image shows 2 different complexes doing the same complex generation on the same object. The upper result shows both interior surfaces oriented counterclockwise while the lower result shows one surface clockwise while the 2nd is oriented counterclockwise.
No clue why different normal orientations are happening.
I'm just a user as you are. Being no Autodesk employee: I do not know where this road will lead to, nor do I claim to've all stuff got right.