Symmetry in maya with Mirror

[Anonymous]

I got a question about how object symmetry work in Maya. I am not sure what I did was intended behaviour in Maya.🤔

I am used to how other software deal with their symmetry like Blender, Zbrush.

So what I found is, when you mirror an symmetrical object A across world, resulting you have object B. When you then modify the object under X symmetry, it will only modify itself. Because I set the symmetry to object A, which only works on a single object.

Otherwise, if you change symmetry to World, when you modify object A, it will also modify object B.

I've attached a picture for this here: 

In another case, if I mirror a symmetrical object (let's call it object A) with Object, with a custom pivot. Then world symmetry will not work, because it is not centred in the world. And if I change the symmetry option to Object, it will only mirror change to other side on itself.  It will not work on object B for some reason.

Just like in this example case:

So, I am assuming object symmetry only works on the object itself, if it is symmetrical. It will not work on stuff you mirrored? Many thanks for answering my question!😀

[hamsterHamster]

Seems that it doesn't work indeed. The workaround then would be to set a key on translateXYZ with AutoKey OFF, then snap move the object to the origin, where World symmetry activates. After editing, when you change the active frame, the object jumps back to its earlier position.

[brentmc]

Hi,

There are a couple of ways you could approach this depending on your goals.

If you always want the second object to mirror the first one you can create an instance. Instances are transform nodes that point to the same geometry. This is a lightweight way of making copies of an object and any changes to the original geometry affect all instances.

1) Edit > Duplicate Special > Options > Instance

2) Scale the instance by -1 in the mirror axis and then move it to wherever you want it

However, if you want to make symmetrical edits but also allow non-symmetrical edits then you would need to keep everything in a single mesh.

1) Mesh > Combine to merge meshes together (or use Mesh > Mirror to mirror a single mesh)

2) Apply local symmetry on the new object to make symmetrical edits

--

Brent 

[hamsterHamster]

@brentmcthanks,

However the post was about Symmetry not working on the symmetrical objects, that are offset and the transforms are frozen. pCube>Translate X>MirrorX> symmetry works only on the original cube > Freeze transform> symmetry is not working at all. Pivot location has no effect on this.

As soon as I move the object back to the Origin and FreezeTransforms, the Symmetry works again. Which is destructive modelling method (the offset information is lost)... the modeller has to do extra gymnastics just to do something [nowadays - really] basic, bad UX.

[brentmc]

@hamsterHamster Thanks for the clarification. I see the issue now.

It looks like local symmetry is not taking the object's pivot into account. I've submitted a bug for that:
MAYA-110094 - Local symmetry not working on mesh with frozen transform

Another workaround is to run Modify > Bake Pivot on the object.

--

Brent

[hamsterHamster]

@brentmcthanks for the bug posting and hints,

I'd add that the location of the pivot is be even irrelevant for symmetry, what needs to be taken in account is the bounding box, its center. It is Mirroring where the pivot is essential.

[brentmc]

It is not so straightforward since symmetry can be used on partially symmetrical models and small asymmetries would perturb the bounding box enough to break symmetry.

Using the pivot is probably more predictable or maybe there needs to be an option to specify what to use?

--

Brent

[hamsterHamster]

Option approach, by default, means more flexibility, which then would be my preference. However, too much options can be confusing, especially for potentially minute symmetry issues, which user even cannot notice. Couldn't it some [geo-]voxel approach, that calculates the symmetry center, based on volume + topology match treshold?