Best practices for maintaining symmetry?

[Segvoia]

Hello all. I am coming back to Zbrush after a 2 year hiatus and I have just upgraded to version 3.1. I was working on a pretty detailed horse model when I noticed that details where not being mirrored correctly as I added them. I’m not certain at what point my model lost it’s symmetry or how, but I’ve spent many hours of modeling on a tool I now know I can’t salvage or use. Oh well, I’ll chalk it up to practice

Browsing the forums I see that the symmetry issue is a common problem in this latest version of Zbrush. My reason for starting this thread was to fish for “Best Practices” to maintain symmetry as I work in ZB3. What would be most helpful to me would be a step by step break down of what I should do at each stage of creation to maintain symmetry form the z-sphere primitive on up to the high poly sub-d finished model. If maintaining symmetry requires taking the base model into a secondary app for clean up, I am considering acquiring either Silo or Wings 3D.

All of your expert opinions are most appreciated.

[aurick]

A common mistake is to be working symmetrically, but have the part of the model that you’re mirroring on hidden. For example, to hide all but one hand and sculpt that hand. These edits won’t be translated to the other hand, even if symmetry is active.

You can usually fix symmetry by going to the lowest subdivision level. Mask one side of the model, then press Tool>Deformation>Smart Resym. Make sure that the axis modifier corresponds to your axis of symmetry. Go up to the next level and press the Smart ReSym again. Repeat for each additional subdivision level until you’ve finished at the highest.

[Segvoia]

Hello Aurick - I didn’t realize that my topic actually posted after trying three times - strange.

I’m familiar with the caveat about having half the model hidden while adding details to the exposed half. I only masked the body off to work on the head, other wise I worked on the whole model.

I tried the tip you posted - masking off one half of the model and then using smart resym. Well, one half of the horse exploded, that’s the only accurate way I can describe it. After holding down shift to rotate the model in steps and then masking off one half evenly, I did notice a funky area between the horse’s ears and between the back legs where I had used the smooth brush. This area would not mask out evenly down the middle. I’m a bit frustrated because I still don’t know if the smooth tool was the cause of this or not.

Another issue I noticed was that after a while the two points on the x axis where not align at the same mirrored areas on the model. This resulted in uneven application of detail on one side of the model.

Now I see others successfully tooling away in this latest version despite the symmetry issue, so I was curious what steps these people were taking from scratch to finish to start their models correctly and to also check and correct symmetry issues along the way? It might appear obvious to regular users of Z but as i mentioned, I’m a half newbie to the software since I only dabbled with it a few years back but now I am approaching it as a serious tool to use in my work.

[aurick]

If your model exploded, then the deformation’s modifier probably didn’t match the model’s axis of symmetry.

[system]

Hello, there.
Long time I’ve visited the support forums.
This is a good thread to start, Segovia.

:b2: On hiding a part of the geometry: very true, while working in symmetry, it’s good to have everything NOT hidden perfectly symmetric, and (inverse) everything symmetric that you’re isolating - not hidden.
People have a tendency to hide the “other half” sometimes, this is wrong, since (if working in ortho, not perspective, view) you won’t have a problem with the other half (i.e. hand) obscuring the other very much. Also, when working like this, it pays to set the pivot to local (usually in right-side bar, also in Transform pallete).

:b2: Having ZBrush-appropriate topology and a perfectly symmetric mesh upon import (if not starting in ZBrush) usually saves the day. This way, I cannot really recall that I had any problems with standard, X mirror symmetry. Good topology practices for this include:

1. Avoid N-gons at all costs - ZBrush will not iterate them the same on both sides.
2. Avoid Triangles - again, symmetry issues - those will not subdivide equally and WILL create “pinch-points” , where all your geometry will tend to concentrate against your will.
3. In the previous app (whatever you’re using before ZBrush) make sure your model is symmetric over x axis at the ORIGIN (the central ceam is at 0 in world x-coordinate).
4. Your sugguestions here…

[Segvoia]

Thank you to you both.
Aurick do you mean that perhaps I didn’t have x axis on when say I used a smooth or move brush?

Megamorph, I was hoping that Zbrush would be an all in one modeling program at this point, but from your post I infer that the surest way to have a clean starting mesh is to construct the base low poly model in a secondary program. I’ve downloaded Wings 3D to play around with the UI. I think I could learn this app pretty quickly.

I found a very useful tutorial and I’m going to use it to create a female figure this afternoon. This tutorial also suggests using a secondary app to make sure the starting low poly model is clean:
http://www.pixologic.com/docs/index.php/Tutorial:_Pinup

[silvaticus]

It happens lots of times to lose the symmetry, especially after doing edgeloops. One fix that someone posted on the forums a long time ago is to unify before the smart resym (tool/deformation/unify+smart resym). I dont know the logic behind it but it works. I would also like to understand why sometimes the symmetry works on subtools and sometimes it doesnt (symmetry was not stored message).

[system]

Segvoia,
In a sence, it’s always good to know other apps & alternatives.
However, I have to give Pixologic a lot of credit for what they’ve done in ZBrush 3.1 with their new topology pipeline. It turns out that now, using ZBrush, you can create any form (character, tree, etc), but then completely re-define the topology.

To do this, you have to create a ZShere over your original geometry (that can have it’s toplogy any way that creates the 3D form you want). With this ZSphere, you can turn rigging on, and then, in the ZShere’s Topology rollout (Tools), go into EditTopology mode. From there, you can re-create your 3D form with the exact toplogy you like (by putting down points, which you can connect with rig-edges, and which will automatically form quadrilaterals for you). Every point you put down, remove, or move will be snapped to the surface of the original high-density mesh.

You can later use either adaptive skin or Projection w/ adaptive skin to make the actual new geometry a separate tool. This provides a cool way to make a low-poly character (for a game, for instance) or mid-poly character with the same form as your original ZBrush model.

There are drawbacks - you have to manually put down each vertex, and that takes time, whereas in other applications, you can model using such tools as outline, inset, extrude, bevel, bridge, and cap, applying them to almost any size and type geometry selection on your model (varies with application.)

One major setback for all ZBrush users is that you cannot define custom / geom. object-specific UV(W) coordinates - texture coordinates, and without a proper way of setting these coordinates, you cannot output your colors to a texture (2D image) in the proper way. I think that if pixologic is not working to solve this within ZBrush yet, they should.

[system]

Continuation of my list here:

4. “N-stars” or “N-edged vertices.” This can happen whether you’re starting in ZBrush or not. What those things are - imagine a vertex with 5 or more edges starting from it and going to other vertices. First of all - this often makes a problem for edge-looping and similar tasks, because you no longer have a continuous segment (in case it is 5, 7, 9 edges - the odds, especially.) Second - this forms really horrible “pinch areas” and pulls your geometry into undesirable places. This does not have any direct implications on symmetry, so I oppologize if I’m going a little off-topic here.
   N-edged vertices are often unavoidable. For instance, when you have a model with a hand and fingers, you will have N-stars in-between places where the fingers start. Treat these areas with extreme care and caution (as compared to purely 4-edged areas.)

5. Your input here…

[Segvoia]

Bumping this thread up for additional replies…

And thanks to all who have responded. I’d really love Rastaman’s input if he happens to pass through

[Tristikov]

Hi, I’m still very new to Zbrush, and I have a question on symmetry;
I’m just starting to sculpt over a new base mesh and when I z-add or subtract with the clay brush, the right side always changes far more drastically than the left, regardless of which side I paint on. With Z intensity very low, the left side will only deform slightly, but the right side will deform quite it bit, often sharply.

Any help or suggestions for managing symmetry would be greatly appreciated!