# Rotation Quaternions

## Transformations

## Rotation Quaternions

A quaternion is a four dimensional vector (x, y, z, w) and to be a rotation quaternion it has to be a unit vector, i.e. x^{2} + y^{2} + z^{2} + w^{2} = 1

We have already used rotate which sets the rotation quaternion of a mesh.

You can check this in the console

mesh.rotate(new BABYLON.Vector3(1, 0 -1), Math.PI / 3, BABYLON.Space.WORLD);console.log(mesh.rotationQuaternion.x);console.log(mesh.rotationQuaternion.y);console.log(mesh.rotationQuaternion.z);console.log(mesh.rotationQuaternion.w);

The same as the *rotation* property the *rotationQuaternion* property sets the orientation of the mesh with the local origin as the center of rotation.

Besides *rotate* you can also obtain a rotation quaternion directly by using, for example

mesh.rotationQuaternion = new BABYLON.Quaternion.RotationAxis(new BABYLON.Vector3(1, 0 -1), Math.PI / 3);

The parameters for the *RotationAxis* method are axis direction and angle. The axis direction vector should be expressed in the world space.

Any rotation quaternion can be converted to Euler angles to use with *mesh.rotation*

const euler = rotation_quaternion.toEulerAngles();

Showing that converted Euler angles to and from rotation quaternion align. Converting Euler to Quaternion Alignment

You can also change the orientation of a mesh using a number of different conventions.

## Warning

You cannot use a *rotationQuaternion* followed by a *rotation* on the same mesh. Once a *rotationQuaternion* is applied any subsequent use of *rotation* will produce the wrong orientation, unless the *rotationQuaternion* is first set to null. Please be aware this often applies when importing models as many of these models already have a *rotationQuaternion* set.

From version 4.0 onwards, the setting of rotationQuaternion to null is done automatically when and only when *rotation* is set directly with a vector, for example

mesh.rotation = new BABYLON.Vector3(0, 0, 0)

Whenever you find rotation errors it is worth setting *rotationQuaternion* to null before updating *rotation*.