Click and drag to rotate

MouseOrbitClickAndDrag.cs

using UnityEngine;
using System.Collections;
 
public class MouseOrbitClickAndDrag : MonoBehaviour {
  
    public Transform target;
    public float distance = 5.0f;
    
	public float xAccel = 0.3f;
	public float maxXSpeed = 0.5f; 
    
	public float yAccel = 0.3f;
	public float maxYSpeed = 0.5f; 
 
    public float yMinLimit = -20f;
    public float yMaxLimit = 80f;
 
    public float distanceMin = 0.5f;
    public float distanceMax = 15f;
 
	public float mapRotationDamp = 0.75f;  
	
	public float scrollSpeed = 5.0f; 
	
    float x = 0.0f;
    float y = 0.0f;
	
	bool doOrbit = false; 
	
	Vector3 lastPos = Vector3.zero;
	Vector3 mouseDelta = Vector3.zero; 
 
	// Use this for initialization
	void Start () {
        Vector3 angles = transform.eulerAngles;
        x = angles.y;
        y = angles.x;
 
		// store the first mouse position
		lastPos = Input.mousePosition; 
		
        // Make the rigid body not change rotation
        if (rigidbody)
            rigidbody.freezeRotation = true;
	}
 
	void Update(){
		if(Input.GetMouseButton(0)){
			doOrbit = true;
			// store the change in mouse input
			mouseDelta = Input.mousePosition - lastPos;
			mouseDelta.x = Mathf.Clamp(mouseDelta.x , -maxXSpeed, maxXSpeed);
			if(mouseDelta.x > maxXSpeed) mouseDelta.x = maxXSpeed;
			if(mouseDelta.x < -maxXSpeed) mouseDelta.x = -maxXSpeed;
			mouseDelta.y = Mathf.Clamp(mouseDelta.y , -maxXSpeed, maxYSpeed);
			if(mouseDelta.y > maxYSpeed) mouseDelta.y = maxYSpeed;
			if(mouseDelta.y < -maxYSpeed) mouseDelta.y = -maxYSpeed;
			
		}else{
			// zero out mouse delta
			lastPos = Input.mousePosition; 
			if(mouseDelta.magnitude > 0.1f){
				mouseDelta *= mapRotationDamp; 
				
			}else{
				mouseDelta = Vector3.zero; 	
			}
			doOrbit = false;	
		}
	}
	
    void LateUpdate () {
	    
		if (target) {
	       	
			// set the x and y euler angles; these are cumulative so they become big numbers (-1400 etct)
			x += mouseDelta.x * xAccel * Time.deltaTime * 1f; // distance *
			y -= mouseDelta.y * yAccel  * Time.deltaTime * 1f; 
 
	        y = ClampAngle(y, yMinLimit, yMaxLimit);
			if(y > yMaxLimit) y=yMaxLimit;
			
			if(y < yMinLimit) y=yMinLimit; 
	 
	        Quaternion rotation = Quaternion.Euler(y, x, 0);
	 
	        distance = Mathf.Clamp(distance - Input.GetAxis("Mouse ScrollWheel") * scrollSpeed, distanceMin, distanceMax);
			
			// not sure what this was doing - subtracting distance on ray hit? 
//	        RaycastHit hit;
//	        if (Physics.Linecast (target.position, transform.position, out hit)) {
//	                distance -=  hit.distance;
//	        }
			
	        Vector3 negDistance = new Vector3(0.0f, 0.0f, -distance);
	        Vector3 position = rotation * negDistance + target.position;
 			transform.position = position;
	       	transform.rotation = rotation;
 
	    }
	 
	}
 
    public static float ClampAngle(float angle, float min, float max)
    {
        if (angle < -360F)
            angle += 360F;
        if (angle > 360F)
            angle -= 360F;
        return Mathf.Clamp(angle, min, max);
    }
 
 
}

this is great. One issue however I've noticed is the movement seems to 'stutter' at regular intervals...