# Rotation

The `Rotation` class encapsulates an object's rotation.

## Example

```
// The following example uses ReactiveModule.rotation(w,x,y,z) to construct a rotation
// from a quaternion-based representation of it. The constructed rotation is used with
// AnimationModule.samplers.polyline to create a rotation animation that is expressed as a RotationSignal.

var SceneModule = require('Scene');
var AnimationModule = require('Animation');
var ReactiveModule = require('Reactive');

// Construct a Rotation object from a quaternion-based values.
function axisRotation(axis_x, axis_y, axis_z, angle_degrees) {
    var norm = Math.sqrt(axis_x*axis_x + axis_y*axis_y + axis_z*axis_z);
    axis_x /= norm;
    axis_y /= norm;
    axis_z /= norm;
    var angle_radians = angle_degrees * Math.PI / 180.0;
    var cos = Math.cos(angle_radians/2);
    var sin = Math.sin(angle_radians/2);
    return ReactiveModule.rotation(
        cos, axis_x*sin, axis_y*sin, axis_z*sin);
}

var time_driver = AnimationModule.timeDriver({
    durationMilliseconds: 2000,
    loopCount: Infinity
});

// Create a rotation sampler using Rotation objects generated
// by the previously-defined axisRotation() method.
var rotation_sampler = AnimationModule.samplers.polyline({
    keyframes: [
        axisRotation(1,0,0,0),
        axisRotation(1,0,0,45),
        axisRotation(1,1,0,45),
        axisRotation(1,0,1,45),
        axisRotation(1,0,0,0)
    ],
    knots: [
        0, 1, 3, 5, 7
    ]
});

// Start the animation
var rotation_signal = AnimationModule.animate(time_driver, rotation_sampler);
time_driver.start();

// Apply the rotation transform to a scene object.
var plane = SceneModule.root.find('plane0');
plane.transform.rotation = rotation_signal;
```

## Properties

This module exposes no properties.

## Methods

This module exposes no methods.


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