Ok thanks Michael, clear now :)

Cheers

Hi Micha,

> Or here - additional polygons at the lower edge ...

Like I mentioned earlier in this thread, it can help for you to switch to Output:N-gons which more clearly shows you where the polygons are coming from.

So for example, with the parameters that you show there if you switch to Output:N-gons, you can see this (viewing from the bottom looking upwards):




Notice how the ngons are not aligned?

In general if you are confused about why you are getting triangles in a particular structure, I would encourage you to switch to Output:N-gons to see how the n-gons are formed. Any place where an n-gon is formed with more than 4 points in it, will end up with that being converted into triangles when you have Output:Quads & Triangles mode.

Now as to why they are divided differently - that is pretty simple, it is because those surfaces have different lengths, here I have discarded the other ones, and you can see that the veritcal one is trimmed back and is not as long as the bottom one:



Because they are of different starting lengths, the longer one gets something like one extra division on it when they get their uniform grids.

I can understand that it seems like they should align like a voxel grid would align - unfortunately it is not feasible for the mesher to use that kind of "intersect with world grid" method because it would only work well on things that happened to be made of planes that were aligned with the world axes. It would produce strange results on anything that was angled.

One of the things that you are asking a lot about are special parameters or things that would help out for a specific model. I can understand that, but just keep in mind that there are a really wide variety of models that the mesher needs to be able to process, there are often all kinds of things that would work great for just one particular kind of model, but that is just not generally practical. Those kinds of things would help you out in one situation and then be really weird and cause problems in a thousand other situations...

- Michael

Hi Micha,

> The initial uv layout should be quite good to create a mesh of quads only or?

No, not good enough to match the parameters - whenever you see adaptive subdivision it means that the initial quad polygon in that area did not match the tolerance and needed to be subdivided.

That's the _only_ reason why things get adaptive subdivision on them...

The part that makes the initial grid has some limits on it to try and avoid creating too huge of a uniform mesh. You can imagine for instance that trying to do a uniform mesh on an object like the one shown here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2379.3 would make for a huge number of polygons.

Also if the surface has varying curvature throughout it like the one you show there, it is not likely to get a dense enough initial grid to avoid all adaptive subdivision, the part that does the initial gridding is more focused on getting a "perfect" initial grid on uniformly curved objects like a cylinder or sphere. It is generally assumed that something with varying curvature may need adaptive subdivision in areas to put more polygons in areas of tighter curvature...

One thing I've been thinking of is possibly adding a setting that would let you turn off adaptive subdivision entirely, that would probably be useful for things like this.

- Michael

Hi Micha,

> Straight upward means something like this ...

I see - of course that would mean making more vertices and more polygons as well instead of keeping the polygon count as low as possible.

It's unfortunately difficult to do this kind of a thing and still keep things all connected overall.

For example making those Straight upwards lines that you show there would mean inserting new vertices on the bottom edge, which means the face flat on the bottom would also need to be altered by that as well.


In the future I do want to work on some more ways to divide a big n-gon up into triangles, but it is pretty hard to do it by inserting more points along the outer boundary since it has this ripple effect of modifying other faces. When you get many faces trying to modify each other at the same time it becomes a big problem. I can more easily add points to the interior of an n-gon which is what happens with centroid triangulation.

- Michael

Sorry guys, I just have one more question Michael, I don't understand why a flat planar surface should be meshed since it's dead flat.

---------

Michael wrote:
"One thing I've been thinking of is possibly adding a setting that would let you turn off adaptive subdivision entirely, that would probably be useful for things like this."

That could be quite useful, since the adaptive meshing can't be controlled yet. Adaptive meshing - that sounds for me like "max error between mesh and NURBS" and could be nice to control the amount of adaption.

Here an example how a meshing could be looking without adative subdivision.



Since the MOI mesher is the best NURBS mesher it could be nice to get full control of the engine, fine tuning for mesh freaks. ;)

Hi Micha - I guess maybe it would help if I knew more of the purpose that you are using your meshes for.

A uniform mesh does have a more beautiful topology if that is the only thing that you are looking for above all else. But at the same time it can have a more ugly shape, more jagged in areas that are curved and normally a higher polygon count than necessary on things with variable curvature since flat areas get the same density as curved areas.

For example notice how coarse the rounded peak of your result is:



Without being able to add local subdivisions just to that area, it results in a very jagged shape there, which is ugly when rendered or viewed in profile, etc...

So except for very special purposes that kind of mesh that you show there is usually worse than one with adaptive subdivision. If you are interested in low polygon count, efficient structure, and making a good looking shape that provides details in curved areas, then those are all things that are going to be negatively affected by no adaptive subdivision.

So that's something to keep in mind...


But yes there are times when people do want clean topology over all else, so for those situations a disable adaptive subdivision would be useful.


Having no adaptive subdivision at all tends to work the best when the shape has totally uniform curvature such as on a sphere or cylinder. That's when a fully uniform mesh does a fine job of fitting the shape properly and efficiently - and in fact you should have probably noticed by now that MoI already does provide that kind of uniform meshing on these kinds of uniformly curved surfaces.


> Adaptive meshing - that sounds for me like "max error between
> mesh and NURBS" and could be nice to control the amount of adaption.

Basically, that's what all the existing meshing parameters do - control the amount of adaptive localized refinement. They also play a role in determining the initial base mesh, but after the base mesh is created then they totally control the "amound of adaption" - for example any polygon that has an angle greater than your given angle parameter will get broken down into smaller pieces - that is exactly what adaptive subdivision is.

So you already have a way to control the amount of adaption - that's all the existing parameters available to you. What I'm talking about is a checkbox that disables any adaptive refinement at all and will only use the base mesh, that would probably help you get the regular meshing you seem to want in some cases, however just be aware that for many purposes such things will actually be worse in shape (or higher in polygon count to make a good shape) as I described above.

- Michael

Hi Danny,

> Sorry guys, I just have one more question Michael, I don't
> understand why a flat planar surface should be meshed
> since it's dead flat.

Sometimes people are interested in getting regularly shaped polygons for specialized purposes. Like for example if you plan to deform the mesh by doing displacement painting on it in zbrush, it is good for the polygons to be diced down to be of a more uniform small size even in areas that are planar (if you are going to do displacements on that planar area).

For other purposes like doing further polygon editing of the mesh, people are interested in getting more regularly shaped polygons with a more aligned topology between all the pieces. Sub-d modeling tends to work best with quad polygons also, so that's why that can come up.

For the most common use of just rendering the mesh, then yeah you don't need planar surfaces to get more polygons than necessary for that.


It all depends on what you are going to be doing with the output data - there are just a lot of varied things that the data is used for, there can be different kinds of meshing needed for these different purposes...

- Michael

> A uniform mesh does have a more beautiful topology if that is the only thing that you are looking for above all else.

I think this would be very useful if you are taking MoI output into a poly modeler for further work - especially if you want to use it as a basis for an SDS model. In this case how the model looks straight out of MoI is not really an issue.

Hi Tony - one tricky thing with using the output for sub-d modeling is that it only works very well for certain special cases, like with just a single untrimmed surface, or a surface of revolution that has not been booleaned.

The way MoI's mesher currently works focuses on making a low polygon count with n-gons. But n-gons can be bad for that specific purpose of using them as a sub-d cage, especially when the n-gons are particularly big and have concave outlines.

Instead of one big n-gon for a planar cap on something for example for sub-d you would rather have a different style of meshing with all surfaces (including planar ones) diced up into regular sized quads, without regard to the underlying surface's UV layout.

That really needs a much different meshing method to make that work well for the general case of trying to convert something like a whole solid to a sub-d... Things would need to be tiled in a pattern that radiated out from the trim edges rather than starting with quads from the underlying UV surface grid which is how the mesher currently works. The way the current mesher works is good for other purposes though like rendering and getting an accurate mesh for STL prototyping, etc... But for sub-d it is not particularly a good fit right now except for limited cases.

Some more info and illustration here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1244.48

- Michael

I remember this product,

http://www.npowersoftware.com/booleans/pboverview.htm

They are trying to output quad mesh sds friendly from booleans operations, it was a smart attempt, but not working that well on something more complex than an hole in a cube. (and even the provided examples are not that good if you close up the object a little bit ...)

< an hole in a cube
very useful indeed :D

> Hi Tony - one tricky thing with using the output for sub-d modeling is that it only works very
> well for certain special cases, like with just a single untrimmed surface, or a surface of revolution
> that has not been booleaned.

You are probably right - maybe one day :-)

Hi PaQ - yes I actually have the same code available for that npower polygon to quad conversion, it is included in the Solids++ geometry library that I use.

I tried hooking it up before, but it just did not give good enough results.

In the future I'd like to try making my own version of that, but it will be a lot of work since it is a completely different mechanism than what the mesher currently does.

- Michael

Allright ... I didn't made the link between npower and solid++ :)

Hello, I'm back with a mesher question. ;)

I meshed a very complex model and tried to get down the polygon count per "avoid smaller than", but if I set a higher number, than the polycount increase too. I have seen this behavoir at other models befor - is it logical or a bug?

Hi Micha, there was a bug in v1 with "Avoid smaller than", are you using v1 or v2 for what you show there?

Otherwise, do you possibly know of one small portion or even one individual surface in your model that is getting more polygons with when you increase "Avoid smaller than"? If you can extract that surface or small portion of the model and send it to me, that would help me to take a look at what might be going on there.

The way that "Avoid smaller than" works, is that if a UV quad polygon is less than that distance then it effectively switches to a coarser angle tolerance of 35 degrees so that those small things will be coarser.

It does this individually for the U and V directions so it can change the way that the mesh is divided, maybe there is some case where that difference ends up generating more polygons due to the way it intersects with the trim boundary, but I would think that would be pretty unusual. So it may be a bug, if I can get an example for me to reproduce the problem over here I'll be able to know more about it.

- Michael

Hi Michael,

I used v2 and sent you a test file. I have seen now that the problem seems to be the fine fence of the air intake, the problem is good to see.

-Micha

polycount of this test 280.000 (1) vs 4000 (0,1) - that is it! ;)

I tested a little bit more - at angle 12 there is a big poly count jump between "avoid.." 0,92 and 0,93. If I set a smaller angle, than the problem appears at a lower "avoid.." value. Could be nice, if the issue could be solved, because the user can't know, when he riched the critical values.

Good luck,
Micha

And here an other problem, I don't get a mesh without a split effect. (the moi screenshot dosn't show the settings for the rendering)