Hi Steve, actually n-gons can give you a more efficient and cleaner structure in certain ways as well. Like in your example model there all the planar surfaces (top and bottom caps and 4 vertical side walls) will just have 1 single n-gon for those spots. Having all quads would require those spots to be tiled into a bunch of little small quad fragments instead of just 1 face.

Having a smaller number of elements like that can be nice in several ways - poly count can be lower, wireframe can be sparser, things like selecting faces for assigning properties can be easier, ... The main thing that doesn't fit is applying sub-d smoothing. But if your model is finished, there is no need to apply sub-d smoothing to it anyway.

On the other hand if you do want to do sub-d smoothing in the general case I recommend using a poly modeler to create the mesh for that since they have tools that are specifically focused on making topology for that particular purpose. In certain special cases you could use MoI for that, like if you use the dicing technique you showed earlier or if you have just a single untrimmed surface that can go into quads more easily but in general MoI's solid modeling toolset and n-gon mesh generation just is not the right tool for the job of producing sub-d quad meshes, it's focused on generating render-ready efficient n-gon meshes instead which is a totally different kind of mesh structure.

- Michael

Actually I was lowering the poly res of the output model to be able to up the res using hypernurbs.
Just as a test of how well you could make a low res cage of a model using moi.
No I wouldn't want to add resolution to an already rezed model. ;)

Just was a fun test that caught my eye.

Here is the block moi file imported into C4D as a lower res poly model shown in the 1st image.
The model was then cleaned up manually using slide points and optimization/welding points.
Then mirrored the 1 quarter part to make a whole.



Now in the second image the final model is hypernurbed by 1 iteration.
It was a quick edit, so didn't pay that much attention to making quads
Detail is still retained. Not sure why you would think it would melt it.....All in how you lay out the polys.



Admittedly for a complex model you might pull your hair out ;)

Hi Chris,

> Not sure why you would think it would melt it.....

Well, try hypernurbing a cube and you will see it greatly change shape, melting down to a kind of ovoid shape similar to a sphere.

Just in general the action of applying sub-d smoothing changes the shape of things like that.

You can reduce the amount of change by having more polygons that don't have very sharp angles between any pair of them. But the shape change is still present, so like I mentioned previously things like vertices that used to be perfectly arranged in a circular shape will not have the smoothed results exactly arranged in a circle anymore.

It's also quite easy for ripples or lumps to be formed in the sub-d result in response to some kinds of topologies. See this video for some examples of that kind of stuff:
http://guerrillacg.org/home/3d-polygon-modeling/subdivision-topology-artifacts

So it's quite possible during this conversion process that some kinds of ripples and bumps will get introduced into what was previously a very exact and smooth NURBS-generated model.

Applying sub-d smoothing does not just automatically "improve" a model in all cases, it modifies the model and the modification is not guaranteed to be always good. Particularly if you had the model in its proper exact shape already (which is frequently how NURBS modeling works - the basic functionality of NURBS modeling involves making exact geometry, things like perfect spheres, carving precise holes in things, etc...), you would not want to apply sub-d do it because you would then mutate it.

If you want things to be kind of melty/lumpy then it's certainly fine, but if that's what you want then you probably should be using a poly modeler to create those types of models from the start. MoI is generally better suited and designed for making models that are well defined by profile curves, it's not focused on melty lumpy type model creation.

- Michael

So for example in this area of your model here:



I wouldn't be surprised if that topology there created a somewhat lumpy shape in that area. Probably not enough for you to notice it just looking at the wireframe or diffuse shaded render, but if you were to make that have a reflective material and then animate it, the reflections would probably squiggle around in that area instead of being very stable, while just exporting a mesh of the original model from MoI and not applying sub-d to it would give you a completely crisp and totally unwavering reflection in those same areas, as long as you got the good vertex normals coming through.

- Michael

Does exist strictly nurbs renderers?

Hi Pilou,

> Does exist strictly nurbs renderers?

You mean something that renders NURBS surfaces without turning it into polygons?

There are a few but it's not very common.

- Michael

< without turning it into polygons?
Yes :)

-> What would there be gained by applying sub-d smoothing

Hi Michael, most of the time I don't touch the topology exported by MoI but for example sometimes I find I need sub-polygon displacement on certain parts and I haven't planned at the start.

Marc

Hi Flashfire,

I see you have gone for really low poly output. That can cause issues as already mentioned by Michael, but you do also have bad flow, which causes problems if sub-d was to be added.

I did not think you would actually attempt that, so I have cut up the model in MOI to show how I would do this. This is at the minimal I would cut the model up, although I would probably do this directly in a Poly modeller.



If I was then to add sub-d(for whatever reason), the model would maintain shape, although I would add hard edges to keep boundaries.




- Steve

Hi Marc,

> but for example sometimes I find I need sub-polygon
> displacement on certain parts and I haven't planned
> at the start.

Could you maybe show an example so I could understand what kind of displacement you're talking about? Do you mean something like painting on some ridges and raised areas?

One method that can work well for that is to import your model into a brush based displacement program - 3D-coat has a voxel method for sculpting like this, which is independent from the initial mesh topology since it converts from a mesh form into voxel form for doing the actual sculpting.

- Michael

Hi Michael,

>>Could you maybe show an example so I could understand what kind of displacement you're talking about?<<

Some applications still use micro-poly displacement based on quads(a direct high sub-d). I know, some(including renderers) now use voxels.

- Steve

Hi Michael,

I was thinking of images maps or shaders like noise applied to a surface in a displacement channel, a bit like a bump or normal.

Here's a example on simple cylinders that has been tweaked a little to keep their original shape while subdividing.

Marc

Hi Marc, but doesn't that render-time displacement that you're showing work on any kind of polygon model, not only one made up of just of quads?

In fact in your example there, it looks like the cylinder to the right has an n-gon cap on the top, not all quads on the top, yet you show it displaced in the rendering?

As far as I can tell, you can do "sub-polygon displacement" in Cinema4D on any kind of polygons - that means to dice any polygons up into smaller pieces before perturbing their vertices by the displacement, the "sub" in this case doesn't mean "subdivision surface" in the same way as a HyperNURBS smoothing.

Here's a quick test just to verify - here's a model that is not suitable for sub-d smoothing, it has not been retopologized into quads only, it's got just 1 big n-gon polygon on the top:



Yet it can still be rendered with a displacement maps with "sub-polygon displacement" enabled:




However, since displacement mapping works in Cinema4D by perturbing vertices around (instead of by perturbing micro polygon render samples which is a way some other renderers operate) you probably want to export such models out from MoI into more finely diced up pieces.

You can do this just at meshing time though, you don't need to retopologize your model into a subdivision surface friendly topology first, you just use the "Divide larger than" option when generating a mesh to dice big polygons up into small pieces (and you may as well just use Quads & triangles instead of n-gons), that looks like this:



Having more regularly spaced vertices like that will make more points available for the displacement mapper to push around. But note that this is just an option that you set when exporting the mesh from MoI, you don't need to totally reorganize the topology of your model for this purpose.


There are some render techniques that do combine displacement maps with subdivision surfaces as well (not sure if this applies to Cinema4D in particular though), but it is typical to be able to do displacement mapping on just regular polygon models. Just generate a diced up mesh if your renderer doesn't incorporate displacment directly into its sampling pipeline like RenderMan.

- Michael

Hi Marc, so in other words you can use the "Divide larger than" export option in MoI to subdivide (as in "dice up into smaller pieces") the generated mesh if you need a more even distribution of vertices.

That kind of subdivision though is not the same thing as producing a "subdivision surface" friendly topology.

- Michael

Hi Michael,

Like said previously, this is a situation were I end up wanting displacement and is wasn't planned, or that it would very long to produce the geometry in a polygonal software.

Here are other examples with the cylinder,
When dicing very small, the vertex normal breaks make funky artefacts.
When dicing very small and unwelding vertices small openings appear.






Anyway this situation doesn't happens often and I'm a happy camper.
Just experimenting a bit. :-)

Thanks for the hints!!

Marc

Hi Marc, you'll probably want to use a welded mesh so that the pieces don't jiggle apart.

Also are you just using the default UV coordinates for that displacement mapping? That's probably what is causing your unwanted disruption at the seam between the top surface and the side.

You'll need to get a continuous UV mapping on your shape if you want the displacement map to also behave as a continuous looking thing across the whole model.

If you were to apply a regular image map to that piece, that would probably show you a similar break between the pieces as well.

I think it's likely that the UV mapping on your other piece is the reason why it behaves how you want, not particularly something to do with subdivision surfaces...

- Michael

Hi Michael, I didn't thought of unwrapping in the previous example, I used the default cylinder mapping because the default Uvmap stretched the texture.

I will try this later on.

Marc

Steve Wow! How did you force Moi to make such uniform polys? I mean I tried to slice but had no luck
like that.

Hi FlashFire,

Sorry, I missed your reply/question.

For that model I just used lines to trim the surfaces. For some models it can take longer to split up the surfaces than actually building the model. But if that is the type of output wanted, then that it what I do.

I did have a look at Topogun due to Michaels post (I had been meaning to look at that program for a while). The program is very easy to use, but find that it would take a lot longer to produce the type of output I want, than it takes me in MOI


- Steve