The original project was created in After Effects 3.1, but has been checked and resaved in v6.5. The Figures below are original v3.1. We've tried to remove or edit the most obvious obsolete information in the text, but your mileage may vary.
When a layer is scaled or rotated in After Effects, it uses the position of the layer’s Anchor Point as the origin for these effects. This month we’ll offer some tips for changing the anchor point and provide examples of the anchor point in use.
Let’s cover some basics for those of you new to After Effects. In a new Comp, create a Solid that’s the same size as the comp (Layer>New Solid). Notice the Anchor Point in the center of the layer. With the layer selected, type “a” to solo Anchor Point, and Shift+“p” to add Position, so only these two properties are displayed in the Timeline window. Both Anchor Point and Position appear to have the same values on the X and Y axis, but what do these numbers mean? Move the layer in the Comp window and notice that only the value of Position has changed. The value of Position is the position of the layer’s Anchor Point relative to the Comp (ie., the Position’s X and Y axis is in “Comp space”).
Double-click the layer to open the Layer window (see Figure 1 below). The Anchor Point is visible in the center of the layer. Select Anchor Point Path from the Controls (now View) popup (shortcut: option-double-click in the Layer Window), and move the Anchor Point around. Only the value of Anchor Point has changed in the Timeline window. The Anchor Point value is the position of the anchor point relative to the Layer itself (ie., the Anchor Point’s X and Y axis is in “Layer space”).
Figure 1. The Anchor Point can be moved and animated by selecting Anchor Point Path from the Controls (View) popup in the Layer window.
Also, the arrow keys nudge either Position or Anchor Point by one screen pixel, depending on whether the Comp or Layer window is active, respectively. The arrows nudge by 10 screen pixels at a time by adding Shift.
When you move the Anchor Point in the Layer window, the image will appear to move in the exact opposite direction in the Comp window. Obviously, this is not very intuitive! But the Position property has no sense of the layer itself; it only keeps track of its Anchor Point in the Comp. Considering the Anchor Point’s position in the Comp window has not changed, but the position of the Anchor Point relative to the layer has, it makes sense that the layer is “offset” in the Comp window. Fortunately, it’s easy to reposition the layer in the comp so that your layout appears unchanged.
Because of this offset behavior, changing the position of the anchor point is best done as soon as you drag the layer into the Comp, and before the layer’s Position has been animated over time. If you’ve already animated the layer by setting Position keyframes, it is still possible to counteract this offset. Select the motion path by selecting all the Position keyframes (click on the word “Position” in the Timeline window and all the keyframes will be highlighted). Now you can move the entire motion path by dragging any one of the keyframes in the Comp window. You can also use the arrow keys to nudge the motion path provided you are “parked” on a selected keyframe (ie., the keyframe indicator is checked).
As you’ve discovered, in order to change the center of rotation and scale without changing your layout, you have to move the Anchor Point and then reposition the layer in the Comp window. But can’t we do this in one step? This is where the Pan Behind Tool comes in useful: it can edit two properties at the same time.
If you read the manual (I’m joking here…), the Pan Behind Tool is intended as a means of preserving the location of the mask in the Comp window while panning the layer inside the mask. It does this by editing two values: Mask Shape and Position. This sounds like a nice feature, but in practice I find it too cumbersome to use.
But the Pan Behind Tool has another function. By clicking directly on the Anchor Point in the Comp or Layer window, you can move the anchor point while maintaining the layer’s visual position in the comp. It achieves this feat by changing the value for both Anchor Point and Position at the same time. Obviously, this is of little use if Position is already animating, unless you want to make a mess of your motion path. But if you set the Anchor Point in the Comp window before creating Position keyframes, it sure beats fussing about in the Layer window.
Beginners sometimes mistake the Pan Behind Tool for an innocent “Move” tool – with disastrous results. When the layer is “moved”, the mask could be dragged completely off the layer, at which point the layer disappears. Don’t panic. Open the Layer window, and select Mask Handles from the Controls popup. You’ll no doubt find the mask on the pasteboard; select Layer>Mask>None to reset.
With this in mind, as soon as you’re finished using the Pan Behind Tool (shortcut “y”), don’t forget to immediately revert back to the selection tool (shortcut “v”) before you start moving layers around.
The online project offers examples of how handy the anchor point can be. For instance, when animating an object such as a rocking horse, the origin of rotation needs to be at the base, not the center of the layer (see Figure 2 below).
Figure 2. By setting the anchor point at the base of the rocking horse using the Pan Behind Tool, the rotation keyframes will animate the rocking motion correctly. Image from PIO’s Classic Nostalgic Memorabilia.
You can also move a layer on an “arc” by dragging the anchor point well away from the layer, and then animating Rotation. Taken a step further, by rotating a full revolution, you can make a layer appear to “orbit” around another object in a perfect circle, as in a moon orbiting a planet.
Transitions where a layer stretches from one corner or side to the other are created by moving the anchor point and animating Scale. For instance, if you set the anchor point on the left side of a layer, and animate Scale from 0% width and 100% height, to 100% width and height, your layer will stretch open horizontally to full screen. An example in the project online takes this a step further, with one layer appearing to push the other one off to create a simple but effective transition.
The ultimate use for the anchor point is for creating motion control moves, popular for panning around photographs documentary-style. It’s important to start with an image that’s much larger than the comp size, so you can avoid scaling past 100% (which will render your image soft and pixelated). If you pan around an image using Position keyframes, you’ll find this works well until you try to simulate a camera zooming in and out by also animating Scale. Because the image is being scaled around the Anchor Point, the larger the layer the more likely it is that the Anchor Point is way off on the pasteboard. As soon as you scale down, the image gets dragged off the comp towards the anchor point.
However, if you position the layer at the Comp’s center, and animate just Anchor Point and Scale instead, motion control moves on large images will feel like you’re pointing a camera with the comp window acting as the viewfinder.
For more complicated motion control moves, where you need to pan, pause and start panning again, here are some additional tips:
Although you can create an “ellipse” shaped orbit by animating the anchor point over time, you might find it easier to create an ellipse motion path using Position keyframes to create a motion path, and then adding Auto-Orient Rotation. [Auto-Orient is now available from the Layer>Transform menu; use the Orient along Path option.] It can be used anytime you need a layer to rotate automatically along a motion path, so it’s very useful for more than just creating orbiting layers.
It’s important to remember that Rotation can still be animated when Auto-Orient is on, and indeed it’s often necessary to change Rotation by 90 or 180 degrees if the object is moving along the wrong axis or upside down.
The other key to getting Auto-Orient to behave is to make sure that the handles for the beginning and ending keyframes are tweaked so that they exactly align with the motion path. The spatial keyframes (ie. the keyframes in the Comp window) default to Auto Bezier keyframes (ie., you’ll see just a “dot” instead of a handle). More often than not, the Auto Bezier handles will be a little off center from the motion path itself. If you don’t tweak the handles, the beginning and end of the motion path will have a twisting motion that looks like a mistake. So click on the “dot” and move it to align the handle with the motion path, and you’ll see that the motion will be smooth at both ends.
The online “7-Auto-Orient Rotation” comp shows the Spaceman layer before and after the handles are tweaked, so you can compare.
Also, sharp angles in the motion path will make the image “jerk” around, usually in an undesirable way. If you have tight angles, turn on Motion Blur so that the fast turns look like an effect, not a mistake!
Additionally, in the “6-Ellipse” comp the center keyframes for the Spaceman are set to “Rove in Time” by clicking the checkbox underneath their keyframes in the Timeline window. This allows for the layer to have a consistent speed across multiple keyframes, or to apply just one velocity curve to the entire motion path.
As mentioned in the text, the Pan Behind Tool is capable of preserving the location of the mask in the Comp window while panning the layer inside the mask. It does this by editing two values: Mask Shape and Position. The stopwatches for both properties need to be on if you’re going to perform a Pan Behind effect over time. This is a nice feature provided you’re willing to give up your position keyframe to the effect. I think I even used it once.
In practice, it’s easier to pan the layer in Comp 1 using simple Position keyframes, and apply a mask in Comp 2. This also allows you to reposition the layer easily in Comp 2 without messing up the pan behind effect.
If you need to crop the layer to a simple square or rectangle, make Comp 1 the same size as the mask would have been if you were using Pan Behind, and the size of Comp 1 will “crop” the layer to the size you need automatically when you nest it in Comp 2. If you need to apply a Mask Feather in Comp 2, then make Comp 1 a little larger, and apply a Mask and Feather in Comp 2.
* Refer to the “Motion Control” Comp in the accompanying project.
If you’ve read Peter Jay Gould’s “Scanning and Panning” feature, DV October 1997, you should be familiar with the concept of using After Effects for motion control moves. However, the article focuses on panning around a photograph. But the layer you are panning could be another composition, in which case you can synchronize events to happen at key moments in the move. For instance, you could pan and pause to focus on a certain item , and have that image glow or animate in some way as if on cue. In this case, turn on the “Synchronize Time of all related items” Preference (File>Prefs>Display Prefs) so that when you move in the nested comp, the motion control comp will move to the same time. [This option is now on by default.]
The online project uses an image taken from PIO’s Classic Fabrics CD. The first comp has a layer where the Brightness is animated (“Fabric setup” comp), and the motion control move then happens in comp 2, “Motion Control”. The image is panned once, there’s a pause while something glows, and then the pan continues to the second and final resting place. When doing pauses, there are a couple of problems you’ll no doubt encounter:
1. For the keyframe that represents the pause (ie., Anchor Point KF#2), this should be toggled to be a Hold keyframe, so that no interpolation will take place between KF#2 and KF#3. If you neglect this step, it’s possible that the layer will wiggle if the bezier handles have been manipulated before Toggle Hold is activated. In any case, it never hurts to turn Hold on if no interpolation is needed. You can change any keyframe to a Hold keyframe by highlighting it and selecting Animation>Toggle Hold Keyframe. Hold keyframes work with any property or effects parameter, not just Anchor Point.
If you turn on Toggle Hold while you’re in the middle of creating the Anchor Point path, then any subsequent keyframes will default to Hold keyframes. You can either select them and Toggle Hold off, or Command-click (Mac) or Control+clikc (Windows) directly on the keyframe icon in the Timeline window to return them to the default Linear (diamond) keyframe.
2. After the pause, KF#3 should have exactly the same value as KF#2 (the Hold Keyframe). You can achieve this easily by simply checking the keyframe box in the Timeline window . Now when you start panning again, there’ll be no glitch or jump.
3. When you try to manipulate the handles for Anchor Point path, you might find the default “dots” hard to find. If so, hold down the Command (Control) key, click directly on the keyframe icon in the Layer Window and then drag out the handle (ie., Command-click-drag in one move). Take care around where KF#2 and #3 are overlapping. You may need to move one of them out of the way so you can get to the handles; in which case, make a note of their exact numerical value, move one of the keyframes, pull out the handles, and then re-enter this value in the Anchor Point dialog boxes to make sure that both keyframes are back in their correct positions again.
© Trish Meyer, CyberMotion, 1998.