- Whenever you transform something
that is move, rotate or scale it,
you need to transform it relative
to some frame of reference.
When you move something,
do you want to move it relative to the world
or relative to the object itself
or relative to the screen and so on.
Reference coordinate system can be chosen
from this pull down list up here are on the main toolbar.
And there are a bunch of options,
we're not going to look at all of these
but just the most critical ones.
The reference coordinate system is sticky
per transform tool.
In other words, you'll have different settings
for move, rotate and scale.
And that's the default behavior.
If you want to change that,
you can do that in the preferences
so that all the transforms
will share the same coordinate system.
But I don't recommend that
because it's really common that you want to, for example,
always move in world or global space
and always rotate in local or gimbal mode.
Okay, so let's talk about
reference coordinate systems in general,
and we'll use the move tool to illustrate that,
if I select some object such as this chair
then if I have the move tool active
we'll see the move manipulator or gizmo.
Let's look at this closely in the various view ports.
If we look in the top view,
we will see that the X-axis of the move gizmo
turns to the right and the Y-axis is pointing up
toward the top of the screen.
And that matches the access tripod we see
in the lower left corner of each view port.
This access tripod indicates the orientation
of the world coordinate system.
The global coordinate system,
or the X, Y, Z axis of our world or scene.
In the top view we see that these things match.
X is pointing to the right and Y is pointing upward.
But if we go over to the front view,
we'll see something different.
If we right clicking that view
so we don't lose our selection,
we will see that X is still pointing to the right
on the transform gizmo and Y is still pointing upwards.
And that does not match
what we see over here in the access tripod,
the access tripod shows Z pointing
towards the top of the screen.
So again,
this access tripod indicates the world coordinate system.
We are currently not operating
in the world coordinate system.
We're operating in something called view coordinates
and we'll see the same if we right click on the left view,
we'll see that X is always pointing to the right,
Y is always pointing upward here
and that does not match the access tripod in this case.
This is the world coordinate system
but we are currently in so-called view coordinate system.
We're transforming in the space of the view port
whatever view port that might be.
So I'm moving in view port X here
that's actually moving in world Y, okay?
So the default is view,
and that's going to allow you to
move things relative to the current view port.
The exception of that
is if you're in the perspective view,
if you're in the view coordinate system
and in a perspective view port,
then the transform gizmo is always going to be aligned
with the world.
So effectively if you're in a prospective view
the view coordinate system is the same
as the world coordinate system.
We can see this,
if I orbit around with halt and middle mouse button
we can see that the move gizmo
aligns with the world access tripod, okay?
So in a prospective view if I move in view X,
I'm moving in world X.
I could explicitly choose to move in the world axis.
I could do that by going up and choosing world,
and that's the global coordinate system.
And now, if we look in any of these view ports
the move gizmo is going to align
with the world access tripod in each one of these views.
So I'm always moving relative to the world.
If I wanted to move in screen space
relative to the view port in a perspective or a camera view,
then I could do that I could explicitly choose screen space.
And now as I orbit around,
we'll see that the manipulator the gizmo
is maintaining the same orientation in the perspective view,
we see that X is always pointing to the right,
and Y is always pointing up.
But as we orbit around, we see that manipulator
or gizmo changing orientation in the other view ports.
So I could use this to,
for example move relative to a camera.
And for example,
if I go here and click on the Z-axis,
it's kind of tricky, but I could click on that Z-axis
and that'll allow me to move the object
towards or away from the camera.
And we'll see, in the other view ports
we're actually moving in three dimensions.
All right, so I'll undo that with Control Z.
So I don't use that very much, but it might come in handy
in certain camera centric situations.
One thing that you do want to do a lot
is move in the local space of the current selection,
I could choose local.
And now the move gizmo is going to be stuck to
the coordinate system of the currently selected object.
And in this case with this chair, it's a group,
the orientation or the manipulator or gizmo here
is aligned with the group's local coordinates.
And so I could once again move
relative to the selected object.
That's very helpful in a lot of situations
where you want something to move
in a straight line relative to itself.
Now, one thing to be aware of
with the local coordinate system,
is that it's actually kind of a temporary coordinate system.
The manipulator is aligned with the pivot point
or the anchor point of the selected object.
And as such, when we look at the position values down here
we will see that they all read out zero.
that's because the manipulator
is at the position of the object.
So were reading out the values
of the object position relative to itself.
And if we click and drag on one of these,
we will see some changes temporarily.
If you look in that transform type in area
we're seeing the offset value we're introducing,
but as soon as we release the mouse,
it snaps back to a value of zero.
Local mode is great for manipulating things.
Just don't be fooled to think that
what you see down here
is actually the position of the object.
It's always going to read a value of zero.
Okay, those are some
of the primary reference coordinate systems
especially the ones that apply to the selected move tool.