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# CMQuaternion

The type for a quaternion representing a measurement of attitude.

```
struct CMQuaternion
```

## Overview

A quaternion offers a way to parameterize attitude. If `q` is an instance of `CMQuaternion`, mathematically it represents the following unit quaternion: `q.x*i + q.y*j + q.z*k + q.w`. A unit quaternion represents a rotation of theta radians about the unit vector `{x,y,z}`, and `{q.x, q.y, q.z, q.w}` satisfies the following:

```objc
q.x = x * sin(theta / 2)
q.y = y * sin(theta / 2)
q.z = z * sin(theta / 2)
q.w = cos(theta / 2)
```

## Topics

### Initializing the Quaternion

[`init()`](/documentation/CoreMotion/CMQuaternion/init())

[`init(x:y:z:w:)`](/documentation/CoreMotion/CMQuaternion/init(x:y:z:w:))

### Getting the Quaternion Values

[`w`](/documentation/CoreMotion/CMQuaternion/w)

The value for the w axis.

[`x`](/documentation/CoreMotion/CMQuaternion/x)

The value for the x axis.

[`y`](/documentation/CoreMotion/CMQuaternion/y)

The value for the y axis.

[`z`](/documentation/CoreMotion/CMQuaternion/z)

The value for the z axis.


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