Straight keyframe-to-keyframe motion doesn't feel natural. Nothing moves linearly in real life—every motion starts and ends completely still, and must accelerate or decelerate to reach a given speed. You can recreate this feeling of natural motion in Earth Studio by "easing" your keyframes.
Easing in the Keyframe Editor
You can add basic easing to your animation straight from the keyframe editor. Just right-click on the keyframe(s) you'd like to ease, and select an option from the menu.
Ease Out creates acceleration from a keyframe. Ease In creates deceleration to a keyframe. Auto Ease adds both Ease In and Ease Out.
For quick easing, you can ⌘ + click a keyframe to apply an Auto Ease.
Easing in the Curve Editor
Clicking on an attribute reveals a specialized view called the Curve Editor. In this view, motion is displayed visually as a bezier curve. Each curve represents the value of the attribute over time. The steeper the line, the faster the motion. We call these lines value curves.
Adding and Adjusting Easing
When a keyframe has easing applied, it's visually represented as an editable easing handle. With these handles, you can achieve complete control over the feel of your motion.
To create easing handles on a keyframe, use the same right-click menu (or ⌘ + click hotkey) as in the Keyframe Editor. Then, click and drag the handles to affect their easing influence.
Modifier keys allow for easy manipulation of existing handles:
- Hold ⇧ to snap an easing handle to a 0° angle.
- Hold ⌥ while dragging to unlink an easing handle from its pair and control it individually.
- Hold ⌘ while dragging to adjust the length and angle of both easing handles simultaneously.
You can also click and drag out from a keyframe, while holding a modifier key, to dynamically set the initial position.
- Use ⌘ to set both handles.
- Use ⌥ to set a single handle.
The curve editor also lets you tweak the values of existing keyframes. You can click and drag keyframes in any direction to adjust their value and timing on the fly. Hold ⇧ to restrict your changes to the horizontal or vertical axis.
Viewing Multiple Attribute Curves
You can view and adjust multiple attribute curves at the same time. Just ⌘ click on attribute names to add / remove them from the Curve Editor. ⇧ click an attribute to add all the attributes between it and the current selection.
Use Esc to exit the Curve Editor, or click on any empty space in the attribute list.
About Value Curves
There are a few things to keep in mind to get the most out of your value curves.
In most cases, the goal of easing is to achieve smooth motion across your keyframes, without any bumps or hiccups along the way. The guiding principle for this is smooth curves equal smooth motion.
As you work, keep an eye on how your value curves enter and exit keyframes. If the curves are smooth, your motion should be smooth.
To create smooth transitions to and from zero motion, you'll want your easing handles to be perfectly horizontal. The longer your easing handles, the more exaggerated your acceleration / deceleration.
You'll also want to try to keep your easing synced across attributes. For example: if you add auto-ease to position attributes, but forget to add it to your pan and tilt, you might notice some unwanted snapping as your camera slows to a stop while your rotation continues linearly.
This is extremely important when dealing with latitude and longitude. These attributes define the path your camera takes as it moves over the world. If they're eased at different rates, your camera will actually take a different path. Check out Multi-View for an in-depth discussion of curved paths.
About Speed Curves
Some animators find it useful to ease with speed curves instead of value curves. The Speed Curve view uses the exact same data as the Value Curve view, but displays it differently: as a graph of an attribute's velocity (or rate of change) over time.
Speed curves function differently from value curves. You can only affect easing and timing; you can't change the actual values of keyframes. Easing handles are present, but they affect the acceleration going to / from a keyframe, rather than the speed itself.
Click and drag a keyframe ↑ / ↓ to change the speed at that keyframe. This can be useful for matching the speeds of two different keyframe segments at the middle keyframe.
Dragging a keyframe's easing handles ← / → will adjust the influence of that keyframe's speed on the following or preceding motion. To keep it simple: long easing handles mean an exaggerated acceleration effect.