Checking and fixing¶

Prove the mirror will be complete before you run it, and know what to do when it will not be.

Check Symmetry¶

Select the mesh and press Check Symmetry. It pairs every face with the settings currently on the page and reports what it found:

headShape: 1 984 of 1 984 faces matched

or

headShape: 1 902 of 1 984 faces matched No seam edge found on the X plane — falling back to spatial matching.

A clean number means the mirror will be complete. A short one means it will quietly skip the difference, which is the outcome worth an extra ten seconds to avoid.

The check works on geometry even in Topology (Maya Symmetry) mode — Maya's symmetry answers "what pairs with this selection" and has nothing to count until something is selected, so the audit is done spatially instead of handing back a page of zeroes.

Select Unmatched¶

Selects exactly the faces the last check could not pair. Look at them in the viewport: the shape of the problem is usually obvious immediately.

What you see	What it means
A scatter of single faces all over	The tolerance is too tight for how symmetric this mesh actually is.
One coherent region	That part of the model genuinely is not symmetric — a strap, an ear, a hair card.
One side of the whole mesh	The mirror plane is in the wrong place, or on the wrong axis, or the space is wrong.
Everything	Axis, space or plane position is wrong; or the mesh is posed and you want a topology mode.

Choosing a tolerance¶

The tolerance is a distance in the space you are mirroring in, so it is in scene units for World and in local units for Object.

Symptom	Do
Faces near the seam pair with themselves or their neighbour	Lower it
A handful of faces have no partner on a mesh you know is symmetric	Raise it
Wildly wrong pairings across the model	Do not raise it — the plane is wrong, not the tolerance

The default 0.001 suits a character modelled at roughly life scale in centimetres. On a mesh modelled in metres, 0.0001 is the equivalent; on a sculpt that has been through a few round trips, 0.01 is often what it takes.

Why a tolerance at all

A "symmetric" mesh is almost never exactly symmetric: an export round trip, a mirror-modelling operation, or a smooth applied once with a slightly different setting on one side all leave floating-point differences. Matching exactly would fail on real geometry; matching without a bound would pair a face with its neighbour. The tolerance is where you say how much drift this particular asset has.

When the mesh is posed¶

Spatial matching cannot work when the two sides are no longer in mirrored positions. Two answers:

Switch to a topology mode — Seam Seed needs nothing but the mesh, and ignores geometry entirely after finding its seed.
Mirror in the modelling pose instead and let the deformation follow. If the mesh is skinned, the landmarks are on the shape and travel with it anyway.

When the model is genuinely asymmetric¶

Some of it will not pair, and that is correct. Two ways to work with it:

Mirror what does pair, then mark the asymmetric region by hand. Use Select Unmatched to see exactly what is left.
Turn on Selected faces only and mirror region by region, so an asymmetric part is never in the source set.

Mirror Selection¶

Not a mirror of assignments at all: it takes the faces you have selected and selects their mirrors instead. No shading changes.

It is the fastest way to answer "what is on the other side of this?" — and it is how you give the two sides different landmarks:

Select the faces of L_cheek.
Mirror Selection — now the right-hand faces are selected.
Assign R_cheek to them.

Reading the result¶

After Mirror Assignments the result line gives you both numbers:

Mirrored 1 984 faces. 82 faces found no partner — try a larger tolerance.

and any notes the run produced — a fallback that happened, a mesh with no landmark faces on the source side, symmetry being off in Maya-symmetry mode. Nothing about a partial result is hidden: the mirror never reports plain success when it skipped something.