# Rotation Quaternions

## 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. x2 + y2 + z2 + w2 = 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.