_randomizeExistingVector3OnSphere (v, base, radius) {
		const rand = Math.random;

		var z = 2 * rand() - 1;
		const t = 6.2832 * rand();
		const r = Math.sqrt(1 - z * z);

		const x = ((r * Math.cos(t)) * radius);
		const y = ((r * Math.sin(t)) * radius);
		var z = (z * radius);

		v.set(x, y, z).multiply(this.radiusScale);

		v.add(base);
	}
Given an existing particle vector, project it onto a random point on a 
sphere with radius `radius` and position `base`.

@private

@param  {THREE.Vector3} v
@param  {THREE.Vector3} base
@param  {Number} radius