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# SCNQuaternion

A representation of a quaternion.

```
typealias SCNQuaternion = SCNVector4
```

## Discussion

A quaternion is a mathematical construct useful for describing rotations in three-dimensional space. Although its implementation differs from that of a 4-component vector, you specify a quaternion value using the same fields as an `SCNVector4` structure.

SceneKit uses unit quaternions (those whose components satisfy the equation `x*x + y*y + z*z + w*w == 1`) for the [`orientation`](/documentation/SceneKit/SCNNode/orientation) property of nodes.

---

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