Smooth rotation around a center

Questions
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1

I am using controllers to rotate an object around a center. I am using the following method to obtain the rotation angle of controllers and then use the angle to rotate the actual object. since I am using x and y of the mouse, the method is not smooth and the mouse pointer need to be moved along x, and y for theta. Is there another way to catch the angle shift around a center? Thank you.

function pointerLocation() {
	var pointer = event.changedTouches ? event.changedTouches[ 0 ] : event;
	var rect = renderer.domElement.getBoundingClientRect();
	var x = ( pointer.clientX - rect.left  ) / rect.width;
	var y = ( pointer.clientY - rect.top ) / rect.height;
	var pointerVector = new THREE.Vector3();
	pointerVector.set( ( x * 2 ) - 1, - ( y * 2 ) + 1 ,0.5);
	return pointerVector;
}

function onPointerDown(event) {
    mouseBegin = pointerLocation();
}
function onPointerMove(event) {
    mouseEnd = pointerLocation();
    deltaTheta = (Math.atan2(mouseEnd.y,mouseEnd.x) - Math.atan2(mouseBegin.y,mouseBegin.x);
}

06