Modeling: Tri, Quad, Triax… which difference ?
DUDU
Posts: 1,945
My main hobby is Carrara, but I like much to test the other softwares !
I noted that there is a difference between them, the shape of the polygons… Why some prefer the triangles and others, the squares ?
Now, there are “Triax”, what is this ?
I'm lost a little, which are the advantages of one compared to the other ?
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Triax is the Genesis and later rigging and weight mapping system. It has very little to do with modeling. It is the skeleton that is attached to the model and how it influences the underlying mesh of the model. I use C7.2 Pro and I can't use Triax based figures because my version doesn't understand the rigging system, although, from what I read when Genesis first came out, was that it was actually a bit closer to how Carrara's rigging or weight mapping system works, than Poser's rigging.
I don't know all the reasons for this, but vertex modelers generally prefer to work with "quads" which are four sided. Triangles are less desirable. I believe it is because they can cause more undesirable artifacts in the mesh or when it is shaded or textured. Carrara can do both.
I don't use Genesis either (c8), how is modelled the character, in squares cut in diagonals or squares cut in cross ?
They would be modeled in quads (squares) just like the V4, M4, V3, M3 type characters. You may have some triangles, but if you look at the mesh in the Vertex Modeler you will find that triangles are very rare.
Another type of polygon that is avoided is what is called an N-gon. I believe the "N" means non, so Non-Polygon. An N-gon is a polygon with more than four points. If you make a model in Carrara that has some N-gons, then it seems to handle it okay. If you were to export that model to use in another program, such as DAZ Studio or Poser, then there may be some problems.
Generally, quads are better because the algorithms used in polygonal modeling like smoothing, subdividing and deformation don't work with triangles very well and will cause artifacts.
Look at the two images:
1. Shows the bended deformation that is smoothed
2. Shows the identical mesh with no triangles side by side with the mesh containing the single triangle. (notice the texture map wonkiness)
3. Also, in animation of polygonal models (non-game models) if triangles exist around joints or eyes or parts that are morphed, unpredictability can occur because the algorithm doesn't know how to handle it.
A great video that explains what happens in subdivision surfaces when triangles or non-compliant polygons are used.
https://www.youtube.com/watch?v=k_S1INdEmdI
Generally, quads are better because the algorithms used in polygonal modeling like smoothing, subdividing and deformation don't work with triangles very well and will cause artifacts.
Look at the two images:
1. Shows the bended deformation that is smoothed
2. Shows the identical mesh with no triangles side by side with the mesh containing the single triangle. (notice the texture map wonkiness)
3. Also, in animation of polygonal models (non-game models) if triangles exist around joints or eyes or parts that are morphed, unpredictability can occur because the algorithm doesn't know how to handle it.
A great video that explains what happens in subdivision surfaces when triangles or non-compliant polygons are used.
https://www.youtube.com/watch?v=k_S1INdEmdI
Thanks for the link and explaining it much more intelligently than me!
OK, that explains why I have sometimes artefacts when I create morphs in objects or characters.
Carrara creates by default some squares cut in diagonals (one direction only), we must untriangulate automatically each object I think.
If I look at your pictures, that seems to have an influence on UV Mapping too.
Interresting link, and thank you for your explanations !
They would be modeled in quads (squares) just like the V4, M4, V3, M3 type characters. You may have some triangles, but if you look at the mesh in the Vertex Modeler you will find that triangles are very rare.
Another type of polygon that is avoided is what is called an N-gon. I believe the "N" means non, so Non-Polygon. An N-gon is a polygon with more than four points. If you make a model in Carrara that has some N-gons, then it seems to handle it okay. If you were to export that model to use in another program, such as DAZ Studio or Poser, then there may be some problems.
Actually, the "n" in n-gon refers to an unknown number....an n-gon has any number of sides. It can have 8, 10, 20, whatever sides. So they use "n" to refer to the fact that you can fill in the number with anything.
And yes, an n-gon is a polygon (since poly also refers to "more than one" or something like that).
There are many reasons why modellers prefer quads, some of which have already been mentioned. Some more include the fact that if you've ever tried to use some of the selection tools on objects with triangles you quickly realize how frustrating and impossible it can be. Ever try to "loop select" on an object with triangles? Doesn't work.
On the other hand, nothing is perfect, and quads certainly aren't perfect. With triangles it is impossible to make them non-planar, which is good. Quads can be non-planar, and it's easy to do. Just move ONE of the points in the quad even a tiny micrometer in the wrong direction and you have a non-planar polygon. Which can cause all kinds of difficulties in rendering (eg, a non-planar might no show up in the render, etc.)
There are many other reasons why modellers prefer quads...some have to do with moving objects between applications, others have to do with how different functions like cloth algorithms handle quads vs. tris, and on and on. There's also the basic desire by many to start with a clean, simple, perfect object like a cube and build your object starting with that simple cube (called "box modelling"). And by definition, when you start with a simple cube you're using quads. It's a very efficient and fairly bulletproof way to make sure your model doesn't have non-planars and other nasty polygons.
Also, keep in mind, that once you have an object built with quads you can always, and very quickly, convert them to tris if your application or some function requires it. But if you start with tris you can never convert them to quads. Well, you can try, but the results are usually pretty nasty.
Actually, the "n" in n-gon refers to an unknown number....an n-gon has any number of sides. It can have 8, 10, 20, whatever sides. So they use "n" to refer to the fact that you can fill in the number with anything.
And yes, an n-gon is a polygon (since poly also refers to "more than one" or something like that).
Ahhh. Okay, that makes sense. Thanks for the clarification on the term.
I recommend this post and this one too as further reading on the tri-quad-n-gon matter. Certainly made it easier for me to explain it better to myself.
I read again all your posts and I thank you for these interesting explanations and your links !
It's the “Genesis system” which I don't understand very well…:roll:
Here's some more interesting stuff on topology - required viewing for all modelers :)
http://vimeo.com/user904568
I believe that all applications convert quads to triangles at render time ?
Careful Roy...I get in big trouble for suggesting general, non-Carrara specific training. Makes folks upset apparently. :)
Careful Roy...I get in big trouble for suggesting general, non-Carrara specific training. Makes folks upset apparently. :)
Yo J2K, I enjoy references and links to general resources, as well as Carrara specific. I also enjoy references and links to specific art resources that are not about Carrara. Your link to the museum sculptures of Ben Franklin was tremendous. I thank you even though I wasn't the person asking questions. Please continue to provide references and links to general art resources, general anatomy resources, and any other resource that you might think is inspirational even if it is not a photo reference.
Just speaking for my personal tastes, what would cross the line would be if someone asked a specific "how do I do X in Carrara?" question and not only did you not answer the question, but you also suggested that the rest of us should not answer the question until you had verified whether or not the questioner had spent sufficient time studying general anatomy. For example, you asked whether Carrara could address "garden hose" crimping in joints. I replied with one method and screenshots related to the question. What I would encourage would be someone also replying with general anatomy references on how joints actually bend, photo references, etc. What would rub me the wrong way would be if someone lectured you that you should not be learning the weight-painting tools until they had verified that you studied anatomy - and furthermore suggested that I should not have answered your question until they had verified such general study.
Again, just my tastes. I hope you continue to post references and links to non-Carrara resources. This includes but is not limited to art resources, biology resources, engineering resources, computer programming resources, and anything else that comes up.