# Rotating and Enlarging Relative to a Centre.

The following two code snippets give the opportunity to place a centre of rotation or enlargement, or pivot, at any time and have a mesh rotate or enlarge relative to that centre.

## Rotate

``````BABYLON.Mesh.prototype.rotateAroundPivot = function(pivotPoint, axis, angle) {
if(!this._rotationQuaternion) {
this._rq = BABYLON.Quaternion.RotationYawPitchRoll(this.rotation.y, this.rotation.x, this.rotation.z);
}
var _p = new BABYLON.Quaternion(this.position.x - pivotPoint.x, this.position.y - pivotPoint.y, this.position.z - pivotPoint.z, 0);
axis.normalize();
var _q = BABYLON.Quaternion.RotationAxis(axis,angle);  //form quaternion rotation
var _qinv = BABYLON.Quaternion.Inverse(_q);
var _pdash = _q.multiply(_p).multiply(_qinv);
this.position = new BABYLON.Vector3(pivotPoint.x + _pdash.x, pivotPoint.y + _pdash.y, pivotPoint.z + _pdash.z);
this.rotationQuaternion = this._rq.multiply(_q);
this._rq = this.rotationQuaternion;
}

mesh.rotateAroundPivot(new BABYLON.Vector3(1, 2, -1), new BABYLON.Axis.Y, Math.PI/4);
``````

The parameters are the position of the pivot (centre of rotation) as a Vector3, axis of rotation as a Vector3 and an angle of rotation a number in radians.

Succesive rotations are accumulative.

## Enlargement

``````BABYLON.Mesh.prototype.scaleFromPivot = function(pivotPoint, sx, sy, sz) {
var _sx = sx / this.scaling.x;
var _sy = sy / this.scaling.y;
var _sz = sz / this.scaling.z;
this.scaling = new BABYLON.Vector3(sx, sy, sz);
this.position = new BABYLON.Vector3(pivotPoint.x + _sx * (this.position.x - pivotPoint.x), pivotPoint.y + _sy * (this.position.y - pivotPoint.y), pivotPoint.z + _sz * (this.position.z - pivotPoint.z));
}

mesh.scaleFromPivotnew BABYLON.Vector3(1, 2, -1), 2, 6, 0.5);
``````

The parameters are the position of the pivot (centre of enlargemen) as a Vector3, scaling in the x, y and z directions as numbers.