# Guide to Game Development/Theory/Mathematics/Quaternions

## About

editQuaternions are used for rotating a geometry and points with along multiple axes of rotation. They exist in four dimensions, and so that have four parts: **w, x, y** and **z**. As **x, y** and **z** are linked and similar to each other, people sometimes use another letter to represent all three, **v** is common for this. To represent them you should store them in a 4-dimensional vector like so: . Quaternions are used as an alternative to Euler angles.

Benefits of Quaternions^{[1]}:

- No gimbal locking
- Interpolation is smooth and direct
- Simple to do calculations with

## Basic creation of a quaternion

editSo if you chose some unit length 3D-vector that you could like to rotate the geometry around ( ) and an amount of degrees that you want to rotate the geometry ( ) then create a rotation quaternion ( ).

There are generally two forms for representing quaternion, short and long. In the short notation it shows it in terms of **w** and **v** (a combination of **x, y** and **z**).

This can be represented in the long notation using **w, x, y** and **z**:

Where ^{[2]}:

If a quaternion is not rotated, then it will have the value^{[3]}:

## Links with imaginary numbers

editThe 4 components (**w, x, y** and **z**) can be broken down into one real number and three imaginary numbers:

where , and are imaginary numbers such that . From that, you can create the following statements:

## Inverse Quaternions

editTo **invert** a quaternion, simply **multiply** the **x**, **y** and **z** components by **-1**.

## Multiplying quaternions

editWhen multiplying two quaternions together, __order matters__ ( ).

The multiple is defined by^{[4]}:

**S**pherical **L**inear Int**erp**olation (**SLERP**)

edit
This is how you Interpolate gradually between two quaternions, like getting a mid-point (or some other point) between two quaternions.

### Superscript notation for Quaternions

editBefore you can do SLERP, you need to understand the superscript notation for a quaternion.

If you have a quaternion **a** and you use the superscript notation to raise it to the power **t**, this means that it will scale the angles inside the quaternion by superscript t. As this only scales all of the angles, this means that the magnitude ( ) of the Quaternion is still **1**.

#### Superscript notation in short notation

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#### Superscript notation in long notation

edit

### The SLERP Equation

editIf your first Quaternion was **q** and the second quaternion was **r** and you wanted to find a point in-between (**p**) which is **t** percent of the way from **q** to **r**, where 0 ≤ **t** ≤ 1.

The final equation is defined as^{[5]}:

## See also

edit## External Links

edit**Youtube:**

- Math for game developers:
- Humane Rigging 03 - 3D Bouncy Ball 05 - Quaternion Rotation
- Hand Calculation of Quaternion Rotation

**Wikipedia pages:**

**Wikibooks:**