A simple primitive sphere solid exported from Moi to Zbrush works fine
but when you divide it in Zbrush holes appear at the 2 polar sides!
I have missed something?
[RESOLVED] You must in Zbrush : Disable the SMT Button Inside the Geometry Menu! (Thx Michael :)

Hi Pilou, did you have welding turned on when exported?

When welding is turned on, it should unify those points at the pole area so that those polygons there are all connected to a single 3d point.

If welding is turned off, then polygons in this type of situation can have their own individual points that are stacked up on the same location - this is usually the cause of the type of behavior that you show there.

Points must be shared between polygons for things like subdivision to cross over them.

But if you have welding turned off, I'm a bit surprised that the seam didn't also pull apart in a similar way.

- Michael

I had enable welding in my previous example
and now disable the welding !
it's now an nother story: it's worst! :)
Star 's Hole + crack :) (2 spheres in the images bottom for show the star hole)
maybe users of Zbrush know the problem?
it's the same for Ngones, quad+ tri, tri...

Hi Pilou, it looks like ZBrush decided to undo the welding for that top pole point.

Some programs might decide to do this on import if they are not set up internally to have different UV texture coordinates for several polygon faces that share one same 3d vertex point.

You need to get that top point welded inside of ZBrush to get the kind of subdivision you expect, you have to have just one point shared in common by all those polygons. Probably there is some kind of "Weld" or "Merge vertices" function for this in ZBrush somewhere, but I'm not familiar enough with it to know where.

You also might try exporting to .3ds with welding turned on - this will actually avoid writing UV texture coordinates to the .3ds file and that might actually help you out in this particular situation since it may avoid the automatic unwelding that ZBrush appears to be doing.

- Michael

That is that!
There were an hidden Menu about import in Zbrush!
So I must make some different try for found the best result!
It was astonishing that a simple sphere make a such result!

But not yet found the graal !

Hiya Frenchy, this seems to be a general problem with zbrush. Testing with a standard modo sphere primitive, I get the same results at the poles.
I think it's worth reporting that at zbrushcentral, you want to do it? ;)

@ rhumba Yes make that if you can :)

HI
It has been over a year since you discussed this problem.
Have you resolve it?
Please advice
I am leaning now MOI, Rhino and ZBrush for jewelry.
I have discovered some tricks and Michael had helped me with some ideas re exporting MOI to Zbrush.
Can you advice please how to solve this in the best way?
Thanks
Olga

Well you know, preparing a cage object for zbrush means 'avoiding' (not sure for the spelling) anything that is not quadrangle. You can mix triangles and quad in some area (if there is no alternative), but it's better to avoid it. Surface subdivision don't work really well on that kind of geometry, and gives bad topology for sculpting anyway.

I don't really see the point of using nurbs, of meshing object from nurbs, for softwares like zbrush. There are so many rules to follow when using poly modeling to create a good low-res zbrush friendly cage object, that I can't imagine any meshing tool clever enough to create it.

Hi Olga, I believe the problem originally mentioned in this thread is that ZBrush decides to automatically "unweld" the points in some particular areas like the pole of a sphere.

Look for an option in ZBrush that may be called something like "weld" or "merge vertices". It may be an import option or a specific command that you can run.

You need to get the polygons to share a single point instead of each one having their own point. When they share the same point between them they will be connected to one another more strongly and will not separate then.

Normally this is achieved by turning on the "Weld vertices along edges" option that can be turned on in the Meshing options dialog box when you save out from MoI (push the little arrow in the lower left corner to expand the dialog to see it). But in this particular case ZBrush decides to "unweld" the points at the pole itself so you will need to use some kind of weld function inside of ZBrush to combine those stacked up points into 1 single point.


ZBrush also will tend to like much more evenly sized polygons, there is some information on how to create a mesh like that here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1549.4

- Michael

Hi PaQ,

> I don't really see the point of using nurbs, of meshing object
> from nurbs, for softwares like zbrush.

Actually I've had several people be successful at doing this, if the base form is easy to define with NURBS but you want to apply some small relief work or other small details on to it, it can work well to combine things in this way.

Here is one previous example:
http://moi3d.com/forum/messages.php?webtag=MOI&msg=1045.1


As far as I have heard it is not so important to get quads in ZBrush as it is to have polygons that are of a more uniform size and even distribution.

Of course normally with output from subdivision surface modelers, they will be all quad output, but as far as I can tell the good thing about that kind of output for displacement is not that they are quads but rather that the quads are all of a nice even size and don't have things like one large polygon directly adjacent to a smaller sized one.

If you use export settings from MoI as described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=1549.4

that should generally help to get that kind of even distribution and sizing as well.


ZBrush also does not handle N-gons properly, so make sure to export with Output: Quads & Triangles instead of N-gons.

- Michael

Hi Olga,

I stumbled over this site & thought it might be useful.
http://www.elancejeweler.com/modeling_tips.html

It's working from Matrix to Zbrush, but as Matrix is a Rhino plugin, the process is still the same.
I've not tried any of it as yet so I can't offer any further advice on this.

Hope it helps, Colin

Hi Olga, some more details on your question:

> It has been over a year since you discussed this problem.
> Have you resolve it?

I just tested with the latest version of ZBrush (version 3.1), and I cannot repeat the problem there so it looks like it has been resolved.

However, please note that it is normal and expected for unwelded meshes to behave like this, those are meshes where polygons have their own points which are stacked up on top of their neighboring points, rather than polygons from different sides sharing one single point.

If you want to avoid this kind of behavior then make sure you have created a welded mesh - to do this when you export from MoI make sure you have the "Weld vertices along edges" option turned on (checked):




Or another option is to use the weld option directly within ZBrush. If you have polygons that are not moving together with one another, you can use the Weld tool which you can find in ZBrush under the Import section on the right side:



That is another option that you can use to edit an unwelded mesh that has disconnected pieces into a single unified set of polygons that share points with one another.

- Michael

Thank you very much for your replies.
Thank Michael I have read the threads you mention and followed all your directions.
ON the pic I attach please see the difficulties I ancounter.

This was made after subdiving the MOI file I attach, with the following settings:
Weld vertices marked
Divide larger than 0.5 Planes
OUtput: Quards & Triangles

When I import it to ZBrush and divide I get some strings (see the pic)
I also did in Zbrush weld and merge in Import menu. I still get the same problem
The thing going from the top is not a problem, I know how to fix it (the flat top need to be subdivided in MOI and the problem solved)


My best idea to resolve this problem is to divide with max polygons when exporting from MOI.
That way I have smooth surface when importing in ZBrush and before subdividing I switch off SMT (smooth)
I still get more polygons and my surface is already smooth when the ring imported and those ugly strings do not appear.

If somebody has better ideas please advice

I move your object for see the curves geneator and kill it for no problem
(normaly obj export don't take care but ...)

So Export in Obj format Weld enable : quad + triangles

In Zbrush
Menu Tool/ import the obj file (your ring)
You are in Edit Mode If not (T)
Select all except the top face (With drag rectangle selection + ctrl)
Menu Masking Inverse selection
Menu Geometry divide (I don't make division for the top)
Menu Masking Inverse selection
Menu Geometry divide (here I had divided twice)
that all ;)
iT's THE PLANE TOP FACE WHO MAKES PROBLEM
With this trick of selection all is cool! You can divide top, and all except Top separately :)

If you want more options Makepolymesh3D

Right Click and Frame for see the divisions

You can maybe control some welding if you want with these cursors TRri2 Quad and Weld

Hello I'm back again :)

From Michael :
As far as I have heard it is not so important to get quads in ZBrush as it is to have polygons that are of a more uniform size and even distribution.


Well I do agree that the 'divide larger than' is a great option that I will love to have in my sub-d package.
Having a nice, clean topology is as important that having uniform surface distrubution.

It's a bit like saying that MoI can provide sub-d ready models, but it's not the case.

- Pole of triangles are problems, everything you'll try to sculpt on pole will be out of control, and you will not be able to sculpt that part as you want.
- Triangles are problems, 1 triangle = pinch effect in your model (you can more less hide the pinch effect with some trick, but the less the better)
- Trimmed surfaces are problems, as the polygon flow will not match.

As far as I know, you can't control all this areas with the today meshing tools.

Here's a closed example of how MoI object will look after a first subdivision is applied.



Working like that is definitively not using zbrush the right way, and you'll miss all the digital painting experience.
Is a non-sence (for me) to create super nice curved smooth surface with nurbs and then
destroy everything by applying a sub-d algorithm over it.

Just my point of vue :)

But in this case in Zbrush you must before the first Divide make some Creases or Crips or Edge loops if you want sharps edges :)

Hi PaQ - definitely a quad topology is more suitable for catmull-clark subdivision like you are showing there.

Displacement-based modeling like ZBrush is as far as I know a completely separate mechanism from that kind of subdivision.

It is true that a displacement based approach wants to subdivide polygons to provide smaller ones to displace, but it is a kind of subdivision that is also oriented towards breaking polygons into smaller pieces, not on following catmull-clark subdivision smoothing rules. (there is a subdivide operation in ZBrush that allows you to do catmull-clark as an option, that is different than the kind of dynamic decimation that will happen for displacement).

As far as I can see ZBrush decimates things into triangles very quickly even if you start with quads.

But it definitely helps if your polygons are of all regular even size.

The example that you show there is all about doing catmull-clark subdivision, that is a totally different kind of subdivision than just direct polygon decimation, as far as I know anyway.

I guess this issue can get confused pretty quickly due to the use of the word "subdivision" in different contexts. It has been a normal thing since the early forms of displacement mapping that the kind of subdivision that happens for displacement is not the same kind of thing as catmull-clark subdivision.


I've been noticing a lot recently that people are tending to ask for "all quads" for many types of situations where the actual need is "evenly sized polygons".


Here's an example - take a large box in MoI and export it to OBJ with plain settings so that it generates an OBJ file with 6 quad faces. Then try to paint on this in ZBrush - it does not work well even though you have "all quad" polygons. For ZBrush's particular use of polygons it is not "quadness" that is so important but "even-ness".

I do not spend a lot of time with ZBrush so it is possible that I don't have the details right, I am just basing the above on what I have observed with some messing around and with what is the typical and normal approach for displacement type subdivision, which is that it is different than Catmull-Clark...

- Michael

Hi PaQ,

> Is a non-sence (for me) to create super nice curved smooth surface
> with nurbs and then destroy everything by applying a sub-d
> algorithm over it.

Yeah, that is definitely correct that you would not approach building a NURBS surface with the intent of trying to sub-d its output later. You generally build it to the smooth shape directly with the NURBS.

But the kinds of things that you might want to do in ZBrush are totally different than sub-d smoothing, things like applying relief designs to "bubble" up from the base surface, distressing a model with pits and craters, adding finer sculptural type details...

Those are things that can be done well with a brush-based displacement type system which is just another totally separate system from a sub-d modeling system.

- Michael

Well I don't know if it's a variation of catmull of not, but the result is quite close ...

And for adding details in zbrush, you have to subdivide your model in, soon ot later.

The only alternative is to do this subdivision with the meshing tool, and don't subivide you model in zbrush anymore. But then, you'll never play with more than 1 ou 2.000.000 of polys, where Zbrush is made to handle 10-15 millions, even 50 millions if you use the HD subdivision technology.

I know exactly what z is made for, I'm using it quite a lot in production.
One the main goal when working with zbrush is to create a displacement map from you're scuplting, and re-apply it in you favorite render software ... So you keep your models light, until the rendering ... where you're again use a catmull/or other sub-d variant, and where bad topology like the example above will get you in trouble.