Maya 2020 fundamentals - modelling the real world
Get halfway through a model and find it's an unworkable mess? Can't add edge loops where you need them? Can't subdivide a mesh properly? If any of this sounds familiar check this course out.
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1
12-10-2012
, 10:18 AM
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Modelling problem
I'm having a problem with Maya in terms of clean modelling. I've attached some images showing the problems. Basically the intention is to export the model as an OBJ into Rhino to use grasshopper to modify/fragment the object in some way, and finally to 3D print, so the model needs to be totally clean.
When I exported the model as an OBJ, and import it back into Maya (2013) to check, some of the normals are reversed (even though they look fine in the original maya file).
When I import into Rhino, some of these problems are more evident, particularly where I've used booleans etc. I've read a few things about booleans being bad in Maya, but sometimes it's the easiest thing to use and for rendering (as opposed to 3D printing/exporting to Rhino/zBrush etc) geometry doesn't seem to be so much of an issue.
As you can see from one of the images, I have a bevelled piece with two holes subtracted from it, so obviously there are some n-gons. I guess the following que's:
1. Can I fix these existing models some how (cleanup is rubbish and doesn't do anything, I can't subdivide the geometry with either cut faces or the split mesh tool). Is there a way to get clean quads from it?
2. If i need to model it, what is the quickest/cleanest way to do it considering there are holes??
Please help! Thanks!
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2
12-10-2012
, 11:39 AM
The thin red line
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PS:what is it that you are modelling......LOL
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12-10-2012
, 12:09 PM
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I know there are a lot of n-gons. I think I got a little lazy when bevelling edges and using booleans, because I didn't see a better way to make holes in those objects and I really can't use split poly on those n-gons with the holes now.
I'm modelling a uniselector from the Colossus machine.
What shall I do with the n-gons???
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12-10-2012
, 12:18 PM
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12-10-2012
, 12:22 PM
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12-10-2012
, 12:58 PM
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12-10-2012
, 01:09 PM
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12-10-2012
, 01:52 PM
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12-10-2012
, 02:24 PM
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The most likely reason your normals appear to be flipping is even with two sided lighting on if you have scaled anything in -1 then they will still appear fine in maya. When you export them to obj they wiell then be "frozen" which effectively sets the scale to 1 and flips the normals.
So to see and fix flipped normals before going to obj select all the objects in your model and freeze their transforms. This will flip any -1 scaled components and they will turn black with show two sided lighting unchecked.
No one has come up with the "magic-make-my-model-all-clean-quads" command yet. If they did they should win a Nobel prize. So if you must have clean quads you will need to work on creating them as you go.
If however, you do not need to smooth your model you can use mesh > traingulate to make it all tri's. However, if the goal is to go to obj to rhino and then obj back to maya and then smooth you'll have a mess.
If your goal is to make water tight models for stl (stereo lithography or 3d printing) you can have all the n-gon and tri's you like so simply boolean the crap out of it and then triangulate the mesh.
I work with someone that makes molds for models and his meshes are horrific but they convert to stl files just fine and he does not get paid for how clean his mesh is, he paid for how many meshes he turns into molds; so spending hours cleaning a mesh that does not require it is just wasted time. The only time you'll have a real problem is if the surface with the ngons becomes non-planar then you will get uneven artifacts and the you will have to clean the edges and shoot for clean even quads or tri's.
update:
I was looking at your mesh images and I did see one thing that is very bad for stl and that is any face with a hole that does not connect to an outer edge. See the attached image. The one on the left is bad, very bad, because you have a hole inside a poly face with no edges connecting to the outer edges.
The second version is better as there is an edge connecting the inner hole to the outer edge of the face the hole is in. You actually only need one edge and you see this in 3ds models all the time. You have two very obvious ngons but for STL they DO NOT MATTER. The face is planar so there will be no artifacts!
The third I have taken a minute or two to make quads. So now the model is all quads but for STL the results of this mesh will be no different then the mesh to the left. So the time to quadrangulate really did achieve anything.
Now please before I get all kinds of hate messages. This only applies if you only need a water tight model, do not need to smooth, do not intend to texture (you have uneven uv spacing so you would want even vertex distribution).
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
Last edited by ctbram; 12-10-2012 at 03:03 PM.
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12-10-2012
, 09:00 PM
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You're right about them being in -1, because I often use -1 scale to mirror a duplicate object. Is this bad practice? I never thought of it as an issue before.
That's interesting about the STL watertight modelling, I didn't know that a floating hole would be so much of an issue.
I guess if I wanted to take the model into zBrush then I wouldn't be able to use a model using the method shown in the middle image because they need to be quads or tris. The right image is ideal.
When you say "This only applies if you only need a water tight model, do not need to smooth, do not intend to texture (you have uneven uv spacing so you would want even vertex distribution)" are you referring to the middle image only? Wouldn't the 3rd image smooth/texture? If not, what then is the best way to model it??
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12-10-2012
, 09:40 PM
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12-10-2012
, 10:06 PM
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"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
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12-10-2012
, 10:18 PM
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About texturing and smoothing. Although the third model is all quads those odd pointy shaped poly faces ("kites") going into the corners would cause issue if you tried to smooth because you could not add control loops easily. I'll add a screen shot to show what you would need to do and maintain that topo. As well as a way to make an even cleaner topo.
For uv distribution and painting, especially in zbrush, you want to avoid areas with really dense concentrations of verts and then areas with large spaces. As you move from high vert/uv concentration to low you will find that your textures stretch.
Here are some examples of that third cube and how I had to add support edges and maintain the odd shaped poly faces and another version where I made a small change and have a much better square poly layout that is easier to add support loops.
You can see the second and third images both smooth okay but the third has a better topology (it no longer has those diagonal diamond shaped poly faces). You can see it has a more regular topo after smoothing as well.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
Last edited by ctbram; 12-10-2012 at 11:05 PM.
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14
13-10-2012
, 12:46 AM
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I'm just wondering how you created the cleaner box with hole, with the additional 8 loops.. I guess one way is to make a cylinder with 2 cap divisions, delete the faces inside the inner division and extrude the faces out, then manually moving the verts to the grid so that it becomes a hole within a square plane then extruding that to create a solid mesh.
I'm guessing you didn't use that method though, just manual split poly tool, using snaps to the middle of the face edges?
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13-10-2012
, 12:48 AM
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"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
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