- [Instructor] Let's talk about reference coordinate systems
for rotations.
So I'll choose the select and Rotate Tool.
And as I do that we will see
the reference coordinate system change
to whatever was chosen
the last time we used the Rotate Tool.
And it's defaulted to view,
or it's just the same as the View coordinate system
for the move tool.
If I select some object, I'll get the rotate gizmo orb.
And in the perspective view, that's going to be aligned
with the world coordinates and an orthographic view.
It's going to be aligned with the view itself.
So if I go over here to the front view and right click
we'll see that the rotate X-axis is going up and down.
The rotate Y-axis is going left to right.
And that's going to be the same when I right click
in the top view, X is oriented up and down
and Y is oriented left and right.
Because we're rotating relative to the selected viewport.
And in this case, if I wanted to rotate
around the world, Z .
I'd be rotating around the top Viewport Z.
I click on this circle here
and I'm rotating around the top view Z-axis,
and that equivalently rotates around the world's Z-axis.
All right.
So that works the same as it does for the move tool.
Let's now talk about World coordinates.
When I choose World coordinates
that's going to display some values down here.
It's going to tell me how the selected object
is oriented relative to the world.
So we can see that I've got no rotations
on X or Y, but I've rotated around Z.
And if I click and drag on the spinner here
we'll see that predictably it's rotating
around the world's elevation axis.
Okay? So that's pretty obvious as well.
Then we come to local coordinates
and this one can be kind of tricky.
The reason is that just like with the move tool,
what we see down here in our Transform Type-In
is all values of zero.
The currently selected object is always going to be rotated.
Zero degrees relative to itself.
This is not telling me what my actual rotation is.
It's just allowing me to see an offset
as I click and drag.
Local mode is useful in a lot of situations.
When you want to rotate an object
around its own pivot or its own anchor point
we'll be looking at pivot points later in the course.
However, local mode is kind of problematic
because it's fake.
It's a temporary reference point.
It's a method that allows us to rotate the selected object
around the objects pivot point.
But that doesn't necessarily correspond
to the actual rotation of the object relative
to its world or relative to its parent if any.
And local mode can actually get you
in a lot of trouble, especially in Animation
you may run into a situation where you rotate some object
just in one axis, like let's say the Y-axis
and you create key frames and you think everything's fine.
You play back your animation and your object spins
around crazy in some completely unpredictable way.
This is a very common thing
with new artists who are not familiar
with how to properly use the Rotate Tool.
Okay? So local mode actually can get you
into quite a lot of trouble.
And again, it's because
it's not the actual coordinate space.
It's a temporary reference that allows us
to rotate relative to the objects pivot point.
But in order to actually have control
and not have unexpected results
we can't really use local coordinates in most cases.
We need to use something called Gimbal coordinate space.
Now, what is a gimbal?
It's actually an instrument that's used
especially in aircraft to indicate
whether that aircraft is level or not.
In this context Gimbal reference coordinate system
displays the actual rotations of the object,
and that's similar to the world coordinates
or the parent coordinates.
Those will show you the actual rotation
of the object numerically, but the key
with the Gimbal coordinate system
is it also gives you visual feedback.
It will show you exactly how the rotational axes
are oriented relative to one another.
We'll look at this in more detail later
but the short version is the rotation axis
are actually sort of parented or linked to one another.
And there's an internal hierarchy or an internal order
in which the X, Y, and Z rotations are applied.
And only in Gimbal mode, will you be able to see this.
So let me go and switch over to Gimbal coordinates.
And it looked like nothing really changed
except now we do see our X value displayed.
Okay. So let's try this out.
If I rotate around that X-axis
which is the red circle, okay, we get some values.
Those are changing up here, and that's good.
Nothing really changed with the actual rotation orb itself
the manipulator or gizmo hasn't changed.
I'll undo that with Ctrl+Z, do the same
with the Z axis and rotate it around world Z.
And we see that the manipulator is following the object
but the manipulator itself isn't changing.
All right, let's try it around the Y-axis
click on the green circle.
And now we see not only is the object rotating
but that X-axis itself is rotating.
The manipulator is showing us the orientation
of the three X, Y, and Z axis relative to one another.
And if I go down here
and rotate around the Y-axis by 90 degrees
then I'll achieve a situation called gimbal lock.
This is an undesirable situation
in which we actually won't be able to rotate
around the access we want.
So I can no longer rotate
in this dimension here because these axes are superimposed.
Hmm. Okay.
Well, this is a big problem with animation
especially with character animation.
You can get into a situation where the joints
of your character spin around in crazy ways
or you actually can't get the animation
to orient or rotate in the way that you want.
At least with gimbal mode, you'll be able
to see the problem I do recommend
when you're animating that you always use gimbal mode
because this is showing
the actual rotational values for one thing.
And it's also again, showing you the relationship
of those rotations relative to one another.
Okay. I can undo that with Ctrl+Z.
Again, we're going to talk more about gimbal mode
and pivot points and all that kind of good stuff later
in the course when we talk about hierarchies,
but for now I just want you to understand
that local mode and world mode
those are temporary reference coordinate systems.
Those are not actually the true rotations of the object.
It's really on only the gimbal coordinate system.
That's going to give you the numerical values
that really exist on that object
and also show you any potential issues that may arise
from the rotational order of the three
axis of X, Y, and Z.