- In the previous movie,
we tried to get a smooth animation
by adjusting key frame values
and tangent handles.
I'll play back the animation and see what we've got.
That technique can be challenging sometimes.
If this were a more complicated walkthrough animation
we might opt to attach the camera
to a spline using a path constraint.
But this is actually a simple case
and that would be over killed.
I covered the path constraint technique in another
course which is 3ds Max: Cinematography for Visualization.
In this case,
we can get very good results using the motion
path feature of the standard position controller.
Stop that animation and rewind.
All we have to do is select our animated object.
In this case, the camera
and go over to the motion panel
and click the button labeled motion path
to access a sub-panel.
Now we see that object's trajectory through space
and this shows why our animation looked
a little bit strange.
The path is not a clean arc.
It's this horseshoe shape here
as seen from the Y axis of the world.
The effect of that is that the camera is moving
in and out along its own line of sight.
We can clean this up
and make it a nice arc using motion paths.
I'll scrub to a different point in time
so we can see these key frames here
a little bit more clearly.
To move a key frame,
all we need to do is select the move tool
and then click on a key frame to select it.
And notice over here,
when we select a key frame,
over here in the motion paths,
we see we've been dropped into sub object, keys.
So we can actually move anyone
or any selection of keys, click and drag.
And we're changing actually
both the trajectory and the timing.
But having done that,
we see that we haven't cleaned up the arc here.
We're still getting that horseshoe shape.
So, undo that with Ctrl+Z.
To get a clean arc,
we need to convert these keys to be Bezier Splines.
Now, that can be a little bit confusing at first
because if you remember from the last movie,
the key frames in the curve editor
already are Bezier Spline Curves
and they have tangent handles.
But the motion path feature we're using here
is a higher level of control.
It's actually another of control.
It's a way to adjust the curve editor splines
from the reference frame of the world coordinates
rather than from a lower level point
of reference of individual key frame values.
And this higher level
of control is a Spline Curve in 3D Space.
The control vertices on that motion path
can be of different types.
For full control of the shape of the curve,
We want the motion path control vertices
also known as key frames here, to Bezier Splines.
So, we'll convert them all to Auto Besier.
Drag a selection rectangle around those
three key frames, go over to the motion panel
and we have key controls, tangents
and a button set tangents to auto.
Click on that and immediately we see an improvement.
We've now got a much cleaner arc.
And now we've actually got tangent handles
on each key frame, but they're hidden
for auto tangent key frames on a motion path.
So unlike the auto tangents in the curve editor,
we can see them in the curve editor
but we can't them here.
And that's okay actually
because it's prevented our view from getting too cluttered.
But if we want to fine tune the animation,
we will need access to those handles.
And the way to do that is actually a little unusual.
In the graph editor,
we can convert from auto tangent to Besier Spline
or a manual tangent by moving one of the handles.
But of course here,
there are no handles to move.
Instead, we have to move the key frame itself.
So, I'm going to select this center key frame here.
Just click on that or drag a rectangle around it
and then use the move tool and just move it.
And now immediately we've converted
that key frame to a manual Besier Spline key
and we have tangent handles on either side.
We can get in close with control our middle mouse.
We can see that the incoming tangent handle
is a green square and the outgoing tangent handle
is a purple square.
And you may have noticed
that in order to reveal those tangent handles,
I had to move the key frame
which in turn changed the shape of the curve.
And actually if we perform an undo operation,
that will move the key frame back where it was
but it will also set the key frame back to auto tangents.
So this is actually a bit of a design shortcoming.
In order to fix this curve, we have to break it.
We have to move that key frame
in order to reveal those handles
and we can't move it back.
So that's just an issue but okay,
now we've got an incoming
and an outgoing tangent handle.
To change the shape
of the interpolation of this Spline Curve,
we can click on one of those tangent handles
and then move it in the usual way
using that move manipulator or gizmo.
Now by default, the tangents are unified.
So moving one of them moves them both.
But we can change that.
We've got a couple buttons over here on the motion panel.
We've got unified tangents and brake tangents.
But it's good to have these tangents unified by default.
That way we're always going to get
a smooth transition through that key frame.
And of course, as always with the move gizmo
we can constrain to various axis.
Click on the bracket to move in X and Y
or just move in X by clicking on the X arrow.
So, I'll dolly back a little bit here,
control our middle mouse.
And I only want to change the length of that handle in
the X axis in order to change the shape of that arc.
And as I do that,
you'll notice that the spacing between these dots
on the path is changing.
And that spacing indicates the speed of motion.
Each one of those dots is a frame.
My current frame rate is 30 FPS.
And the distance between those dots is
the distance traveled in one 30th of a second.
If the dots are close together,
like at the ends of the arc
then the object is moving more slowly.
If the dots are far apart, like in the middle
then the object is moving more quickly.
Okay.
So let me design this.
We'll art direct this,
we're trying to get a clean arc there.
Set that sort of like that.
So we're getting more, more of a circular shape
and then let's see what we get.
We'll rewind and play back.
And I do think we've improved this
but we can actually make it a little bit better.
I think what I want to do here is select
the key frame and move it in the negative Y axis.
So we'll get kind of a more exaggerated arc there.
Rewind and play that back.
Okay.
So let's say we're happy with that.
Just remember that again,
editing the motion path actually changes
the function curves on the position tracks.
We can of course go back into the curve editor
and adjust the function curves directly,
but be aware that unless you're careful
you will end up changing not only the timing
but also the shame shape of the resulting motion path.
For example,
you may want to adjust the slow in
or slow out without altering the trajectory
or the shape of the path.
Then you would need to use the locked tangents
feature we saw in the previous movie.
Only then could you adjust the tangents
of multiple key frames simultaneously
while maintaining their proportion relationships
which would change the timing
without changing the trajectory.
Alright, that illustrates the effectiveness
of a motion path to edit position key frames.
And that concludes our chapter on animation.