- [Instructor] Symmetry is a modifier
that gives us the ability to model bilaterally
or radially symmetrical objects,
and weld the seams at the same time.
That way we can avoid any issues along that seam,
that might arise when we add subsequent modifiers,
such as OpenSubdiv.
I've prepared a box primitive here
such that it's got an open border,
and the pivot point is positioned exactly on that border.
The reflection plane of the Symmetry modifier
will be placed at the pivot point by default.
With the object selected I'll go to the modify panel,
and from the Modifier List, we'll add a Symmetry modifier
we can just type in SY, and click Symmetry.
The Symmetry modifier has two modes
available from a pull-down list, Planar and Radial.
We do want a Planar reflection, and that is the default.
We can choose up to three mirror axis here
to reflect the shape in three different directions.
The default mirror axis is Z.
The reflection plane is displayed as an orange, plane gizmo,
and it's currently coincident with the X, Y plane
of the object pivot or the object's anchor.
With the result that the object is reflected in the Z axis.
We don't want that we want to reflect in the X axis,
so let's disable the Z Mirror Axis, and enable X.
Now, the reflection gizmo
is oriented with the Y, Z plane of the object,
and the object is reflected across the X axis.
The really great thing about the Symmetry modifier
is that it automatically welds the seam vertices.
When Weld Seam is enabled, we get a solid box with no gaps.
That's actually very important
especially when we add a subdivision surface modifier.
Even if a gap is not visible, it can be an issue.
Any seam in the control cage
would result in two separate elements
or two separate shells.
And that might cause a problem along that seam
maybe even an ugly crease in the subdivided model.
At this point, we can see the result of the symmetry.
If we go into the Editable Poly base object,
and enable Show end result,
we can then go into any sub object modes such as vertex
and start moving things around.
It's getting closer in the top
that you control all middle mouse,
and maybe select these vertices here at the corner
by dragging a selection rectangle.
Grab the move tool,
and move those around and we can see that we're getting
a symmetrical effect on the other side of the model.
All right, cool, symmetry is working.
We can now add our OpenSubdiv modifier.
Let's exit out of sub-object mode.
Go up to the top of the stack
by clicking on the Symmetry modifier.
And we'll add OpenSubdiv,
click on the modifier list, type in an OP
and select OpenSubdiv.
We've got one iteration to the Subdivision by default.
We can leave it at that for now.
All we need to do to edit this,
is to once again go back into the Editable Poly base object,
and with Show end result,
we can go into some sub-object mode, such as vertex.
And once again, move that around,
and we can see that we're not only getting Symmetry,
but we're also getting an OpenSubdiv
or Subdivision surface smoothing effect,
and that's happening after the Symmetry,
so we're getting a clean seam here with no gaps.
To make the display a little bit clearer.
You might want to disable edged faces
just press the F4 key on your keyboard.
Now we don't see those isolines,
and we get the control cage superimposed over the model.
And this is great
because we have the best of both worlds here.
We can see the control cage,
and manipulate those control cage vertices for example.
But we can also see the end result
of the subdivided model on the reflected side.
It's generated by the Symmetry modifier.
When modeling with Symmetry,
we need to be careful about the points along the seam
or the reflection plane.
If we get in really close
and select a vertex along that seam,
if we move the vertex in the negative X axis
we don't really see any problem,
but if we move it in the positive X axis, we create a gap.
The reason it looked okay when we moved it across the seam
in the negative X axis, is because the Symmetry modifier
automatically welds the seam there.
However, if we moved too far in the positive X direction
away from the seam, then eventually we'll create a gap.
That area is not being welded,
and that's because that point and it's reflected neighbor
are too far apart.
They're farther apart than the weld threshold.
Okay, let's undo that with Control + Z.
By the way, it's not strictly necessary
to model a symmetrical object right at the origin
as I've done here or at an X position of zero,
but it is recommended because that will make it easy
to move these points back to an X position of zero,
which is the seam or the reflection plane.
It just happens as you work,
that sometimes you can accidentally create gaps.
And if your model is right at the origin
then you can fix that really easily
by just typing in an X position value of zero
for the vertex.
Let's now talk about other sub object modes
we can manipulate edges and edge loops.
Let's go into edge sub object mode,
and we can select an edge loop just by double clicking.
So we can double click on an edge loop to select it.
And we can transform that, for example, we can scale it.
Grab the scale tool, and we can scale in the Y axis,
and we can see that that's having an effect on
the reflected side of the model as well.
We can undo that Control + Z.
Likewise, we can scale in Z and just the same thing happens
we can see the effect on the reflected side of the model.
Very good, I'll undo that with Control + Z.
However, if we try to scale in the X axis
we're probably going to have problems.
So I'll select a different edge loop,
double click on one of these that's running parallel
to the X axis.
Click and drag on the X axis of the scale gizmo,
and we immediately see a problem there
we start getting a gap once again.
Okay, I'll undo that.
To avoid this problem we can scale relative
to the object's pivot point,
which is right at the seam.
And we'll do that by using Transform coordinate center.
Up on our main toolbar we have the Scale tool active,
and we can choose its Reference coordinate system
from this pull-down list.
If we were scaling at the object level,
and we wanted to scale relative to the pivot point
we could just simply choose Local coordinates.
But unfortunately, that does not work in sub-object mode.
We need to choose the object
as its own Reference coordinate system.
And then additionally, use Transform coordinate center mode.
From the Reference coordinate system pull-down list,
choose Pick, and then click on the object
that you're working on.
So I'll click on that seat cushion.
I see it's name displayed up here,
but that name is truncated.
If we open up the Reference coordinate system pull-down
we can see the entire name there,
Chair task bottom cushion.
So that's going to be our reference point for transforms.
To make that active,
we need to go to the Transform center button here,
that's a fly out.
Hold that button down and choose the bottom icon,
which is Transform coordinate center.
Once we've done that, then the gizmo snaps
to the pivot point of the object that's chosen up here.
Okay, so click and drag on the X axis once again,
and we can see that we don't have any issues
with creating any gaps no matter what we do.
We can do that in any view port,
maybe go up to the top view, double click on an edge loop,
and scale in the objects X axis.
And since the pivot point is right on that seam
we don't incur any problems with generating gaps
or any other possible issues.
All right, so that's the basics of using Symmetry
in combination with Subdivs.