>>Additionally with CAD model imports, the vertex normals are very accurate because they come from the original CAD data. Things like a part with a sphere in it will have the exact vertex normal from the original sphere surface, etc... There's no way for something that cooks up normals just by averaging already faceted data to come up with the precise original normals like that.<<

What?

The problems with smoothing of exported meshes from "nurbs surface->mesh" exporters is due to the bad topology, mainly around the boundary's of joined curved surfaces. If you export a sphere from MOI then render it with vertex normal info or with smoothing, then you would have to guess which was which, as there is no difference due to poly flow. It is the same with the model I showed sliced up. If I render that with vertex normal info or smoothing, the results are the same.

What vertex normal info is good for, is hiding the bad topology/ bad poly flow output from the conversion.

Hi Steve (STEVE_HOME),

> The problems with smoothing of exported meshes from
> "nurbs surface->mesh" exporters is due to the bad topology,
> mainly around the boundary's of joined curved surfaces.

It's not quite so simple as "bad topology" - doing shading by automatically creating vertex normals is sensitive to many kinds of topologies like just a big polygon next to some small ones.

You get easily get shading glitches with models purely created within the polygon environment with smoothing groups and break angles unless you have very regularly sized and distributed polygons. That's not just "good topology", it's kind of "restricted topology".


> mainly around the boundary's of joined curved surfaces

Yeah, it's also due to issues like a change in shape happening at the boundaries as well.


> If you export a sphere from MOI then render it with
> vertex normal info or with smoothing, then you would
> have to guess which was which, as there is no difference
> due to poly flow

If you had something that was only one portion of it as a sphere and then it transitions to some other shape adjacent to it, like a fillet or something like that, that's when you won't get the same kind of exact normals for each piece automatically cooked up just from facets.

You're right that just within the middle part of a the sphere that automatically generated normals are ok, that happens to be in an area where the polygons are going to be all regularly sized and distributed.

- Michael

Hi Steve,

> What vertex normal info is good for, is hiding the bad
> topology/ bad poly flow output from the conversion.

This is not quite accurate - the vertex normal info doesn't just hide bad topology, it ensures that the rendering is shaded using the exact same shading from the original CAD model.

But yes this happens regardless of topology.

It's not just about diffuse shading, using the exact vertex normals also gives reflections that will be true to the original NURBS geometry.

Normals that are cooked up automatically by averaging of facets can often have things like shimmery or wavering reflections in areas of shape transition. The normal generation gets affected by the topology in that case, and it's quite difficult to get the perfect polygon topology on many areas of transition.


> It is the same with the model I showed sliced up. If I render
> that with vertex normal info or smoothing, the results are
> the same.

Possibly not if you look at reflections in some areas where you've got some elongated diamond shape quads. Did you ever post any model file of the cut up version? If you can post that I'll see if I can find an area that shows a difference in reflections.

- Michael

Hi Steve (STEVE_HOME), here's an example of the kind of thing that I'm talking about re: spheres - here I have taken the original block and cut some sphere pieces out of it and have some fillets and another cut as well. Not a whole lot of stuff but it looks like this now:



Rendering this with exported vertex normals will render all those sphere pieces as perfect spheres, including absolutely no wavering in the reflections.

Good luck trying to create a polygon topology that recreates the same level of crispness in the reflection in the boundary areas... The problem gets more and more difficult when the boundaries become even more irregular like with a some more trims cut out or little holes in the middle of larger faces, stuff like that.

Particularly when you have a mixture of little features like a little hole or notch next to broader surfaces, it becomes quite difficult to get an evenly spaced and sized polygon topology to go on such things. And any kind of unevenness in the polygon topology will affect automatically created vertex normals done by averaging facet normals.

- Michael

Hi Michael,

>>Good luck trying to create a polygon topology that recreates the same level of crispness in the reflection in the boundary areas...<<

Interesting little challenge. I will have a bit of spare time later, so will see what the results look like.


- Steve

If you try to do that with poly modelling and automatic smoothing normals, you are going to have to put a small ring of polygons to protect each flat surface as it transitions to a curved surface or you will get artefacts on the flat surface. In Modo, you would do a small inner bevel on each flat surface to do this or a loop slice. However this model is quite complex and I think you will struggle.

Hi Steve (SteveMacc),

> However this model is quite complex and I think you will struggle.

And even though the model is difficult to handle for that kind of task, it's not really that complex of a model itself overall. For example it only took me something like a minute to create it.

The other kind of thing that tends to be difficult to apply a quad-only topology to is when there are some holes bored through things, particularly when the holes are of different sizes or are nearby each other or nearby boundary edges. When that happens the technique of adding a ring around each feature edge is hard to maintain because the rings are colliding with each other too rapidly.

- Michael

Hi Michael,

>>The other kind of thing that tends to be difficult to apply a quad-only topology<<

So you want my example to be only quads,... OK, I will do that if you can output a mesh of this model from MOI with no tri`s


- Steve

Hi Steve,

> So you want my example to be only quads,...

Do whatever you wish with your example - your previous one that you posted here: http://moi3d.com/forum/index.php?webtag=MOI&msg=3869.48 seemed to be constructed with all quads, so I thought that was what you were going for.

But if you produce one with triangles in it I wonder if you will consider it to be a "bad topology" yourself though?

- Michael

Hi Michael,

To me, tris would only be classed as bad topology if they where isolated, surrounded by quads/terminating at edges forcing bad flow. In the model where you have cut partial spheres, then you have poles, yes, the poles can be terminated with quads, but the quads would need to be extremely small due to you wanting correct reflection rather than just stopping rendering artefacts.

As I do not haver a lot of spare time, I will just make a section of the model from quads.

Does that mean you will not be making a mesh output from MOI with no tris? :)


- Steve

Hi Steve,

> Does that mean you will not be making a mesh
> output from MOI with no tris? :)

Well, I'd like to but it probably won't be happening anytime too soon... I've looked into various techniques for possibly doing that, and it would be possible to make something that worked ok for some simple kinds of cases but very difficult to make one that would be very robust.

- Michael

Hi Steve,

> due to you wanting correct reflection rather than
> just stopping rendering artefacts.

A reflection that looks wavery and jittery _is_ a type of rendering artifact. But of course you won't notice it if you do a rendering without any reflection in it.

Reflection tends to substantially amplify any problems like little wiggles in geometry or irregularity in normals.

It's just another area that you don't have to worry about if you render with the NURBS vertex normals being used.

- Michael

Hi Michael,

In real world, most reflections are not perfect as most surfaces are not perfectly smooth.

As for edges. I do know about adding insets/extra edge loops for controlling smoothing. The good thing with that is edges can be made to look natural/not "knife edge sharp" without added geometry, although if needed, hard edges can be added to force termination of smoothing at boundaries.

 

- Steve

Hi Steve,

> In real world, most reflections are not perfect as most
> surfaces are not perfectly smooth.

Yup, but that's one of the cool benefits to NURBS - you can do things like easily create spheres that are perfectly smooth. Then if you want them to not look smooth you put stuff like a texture on them, it gives you more options that way.

It's a whole lot easier to add in imperfections if you want them, than it is to remove imperfections if you don't want them.


That's kind of the whole reason for existence of NURBS in general - so that you can make a kind of idealized geometry design for your object. It's why manufactured objects use NURBS geometry for the model definitions for the most part.

I'm not sure if I really understand your point about "in the real world".... - surely you don't think that every kind of rendering is only about trying simulate the imperfections of the real world, right? There are various kinds of rendering styles, some of which are about making illustration type results.

- Michael

Hi Michael,

>>I'm not sure if I really understand your point about "in the real world"....<<

"In real world", = not a computer simulation/render, actually outside in the world :)

I have managed 15 minutes to make part of the model, will finish the section off (if time) when I get back from city centre.
Monday morning blues on a Tuesday :)

- Steve

Hi Steve,

> "In real world", = not a computer simulation/render,
> actually outside in the world :)

Uh ok, but the discussion here is actually about rendering...

You said:

"In real world, most reflections are not perfect as most surfaces are not perfectly smooth."


Was I supposed to interpret this as just some random fact completely disconnected to the discussion at hand?

I took it to mean something like: In the real world most reflections are not perfect, so it's ok for them not to be perfect in a rendering as well.

- Michael

Hi Michael,

I wish I had as much spare time as you to continue this fruitless discussion on what "real world" is, but I have not.


- Steve

Hi Steve, well I understand what the real world is.

What I don't follow is the purpose behind you bringing that up - were you trying to make some correlation between the real world and what a rendering should look like, or not?

If your comment had nothing to do whatsoever with the actual discussion, it might be better to just leave it unsaid.... It's pretty natural for someone to assume it had some kind of intended relevance to what was being discussed.


I have to admit, I'm pretty confused about a lot of things in this thread, like what is the motivation to do all this work to reorganize all the polygons when the ones that were just directly saved out from MoI with the accurate vertex normals on them generate an already perfect looking rendering.

I guess some of these things will just remain mysteries to me.

- Michael

Being a newcomer in these forums I didn't want to jump in, but after following this thread for a few days let me just praise Michael's composure in a discussion that might have stopped at post n.85 (or even before).
Reading some posts I had the feeling that people is speaking different languages or just refuse to understand. Meh!

Hello Michael,

>>I have to admit, I'm pretty confused about a lot of things in this thread, like what is the motivation to do all this work to reorganize all the polygons when the ones that were just directly saved out from MoI with the accurate vertex normals on them generate an already perfect looking rendering.<<

As I put forward earlier in the thread, I make models with quads due to that is what is wanted. I do not turn around to a customer and tell them "you really dont need that" and send them a model with n-gons/tris, then say, well it renders perfectly. If I did, then I would lose the work/contract.


- Steve