Control over y-axis limit in rotating object by touch

Hello,I am 3d artist but less into scripts.Need help to resolve my issue.Found script for rotating object by touch but my problem is i need to control over y-axis limit in down direction(require upper- hemisphere rotation)only. below is the code:

using UnityEngine; using System;

 public class TransformObject
 {
     ///////////////////////////////////////////////////////////////////////////
     #region Variables
 
     // variables
 
 #if UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_WEBPLAYER
     private float RotationSpeed = 1500;
     private float MoveSpeed = 10.0f;
     private float ZoomSpeed = 15.3f;
 #endif // UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_WEBPLAYER
 
 #if UNITY_ANDROID || UNITY_IPHONE
     private float RotationSpeed = 15f;
     private float MoveSpeed = 1.09f;
     private float ZoomSpeed = 0.009f;
 
     private float mOldFingerDelta = 0;
     private const float mFingerDistanceEpsilon = 1.0f;
 
 #endif // UNITY_ANDROID || UNITY_IPHONE
 
     public float MinDist = 2.0f;
     public float MaxDist = 50.0f;
 
     private Transform mMoveObject = null;
 
     #endregion
     ///////////////////////////////////////////////////////////////////////////
 
     ///////////////////////////////////////////////////////////////////////////
     #region Public methods
 
     /// <summary>
     /// 
     /// </summary>
     public TransformObject()
     {
         EnabledMoving = true;
     }
 
     /// <summary>
     /// Sets transform that will be used as "center" of the rotate / pan / zoom
     /// </summary>
     public void SetTransformRotateAround(Transform goMove)
     {
         mMoveObject = goMove;
         if (mMoveObject == null)
         {
             Debug.LogWarning("Error! Cannot find object!");
             return;
         }
     }
 
     public void Update()
     {
         if (!EnabledMoving)
         {
             return;
         }
 
         Vector3 dir = mMoveObject.position - Camera.main.transform.position;
         float dist = Math.Abs(dir.magnitude);
 
         Vector3 camDir = Camera.main.transform.forward;
         Vector3 camLeft = Vector3.Cross(camDir, Vector3.down);
         Vector3 camDown = Vector3.Cross(camDir, camLeft);
         //Vector3 camUp = Vector3.Cross(camLeft, camDir);
 
 #if UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_WEBPLAYER
 
         float dx = Input.GetAxis("Mouse X");
         float dy = Input.GetAxis("Mouse Y");
 
         // rotate
         if (Input.GetMouseButton(0))
         {
             mMoveObject.Rotate(camLeft, dy * RotationSpeed * Time.deltaTime, Space.World);
             mMoveObject.Rotate(Vector3.down, dx * RotationSpeed * Time.deltaTime, Space.Self);
         }
 
         // move
         if (Input.GetMouseButton(1))
         {
             Vector3 camPos = Camera.main.transform.position;
             camPos += -camLeft * MoveSpeed * dx * Time.deltaTime;
             camPos += -camDown * MoveSpeed * dy * Time.deltaTime;
             Camera.main.transform.position = camPos;
         }
 
         // zoom
         if (Input.GetAxis("Mouse ScrollWheel") > 0)
         {
             if (dist > MinDist)
             {
                 mMoveObject.Translate(-dir * ZoomSpeed * Time.deltaTime, Space.World);
             }
         }
 
         if (Input.GetAxis("Mouse ScrollWheel") < 0)
         {
             if (dist < MaxDist)
             {
                 mMoveObject.Translate(dir * ZoomSpeed * Time.deltaTime, Space.World);
             }
         }
 
 #endif // UNITY_STANDALONE_WIN || UNITY_STANDALONE_OSX || UNITY_WEBPLAYER
 
 #if UNITY_ANDROID || UNITY_IPHONE
 
         // rotate
         if (Input.touchCount == 1)
         {
             mMoveObject.Rotate(camLeft, Input.touches[0].deltaPosition.y * RotationSpeed * Time.deltaTime, Space.World);
             mMoveObject.Rotate(Vector3.down, Input.touches[0].deltaPosition.x * RotationSpeed * Time.deltaTime, Space.Self);
         }
 
         if (Input.touchCount == 2)
         {
             UnityEngine.Vector2 deltaFingerVec = Input.touches[0].position - Input.touches[1].position;
 
             float deltaFingerValue =
                 Mathf.Sqrt(deltaFingerVec.x * deltaFingerVec.x + deltaFingerVec.y * deltaFingerVec.y);
 
             // move
             bool moved = false;
             {
                 float moveX = 0;
                 float moveY = 0;
 
                 // moveX
                 if (Input.touches[0].deltaPosition.x < 0 && Input.touches[1].deltaPosition.x < 0)
                 {
                     moveX = Mathf.Max(Input.touches[0].deltaPosition.x, Input.touches[1].deltaPosition.x);
                     moved = true;
                 }
                 else if (Input.touches[0].deltaPosition.x > 0 && Input.touches[1].deltaPosition.x > 0)
                 {
                     moveX = Mathf.Min(Input.touches[0].deltaPosition.x, Input.touches[1].deltaPosition.x);
                     moved = true;
                 }
 
                 // moveY 
                 if (Input.touches[0].deltaPosition.y < 0 && Input.touches[1].deltaPosition.y < 0)
                 {
                     moveY = Mathf.Max(Input.touches[0].deltaPosition.y, Input.touches[1].deltaPosition.y);
                     moved = true;
                 }
                 else if (Input.touches[0].deltaPosition.y > 0 && Input.touches[1].deltaPosition.y > 0)
                 {
                     moveY = Mathf.Min(Input.touches[0].deltaPosition.y, Input.touches[1].deltaPosition.y);
                     moved = true;
                 }
 
                 Vector3 camPos = Camera.main.transform.position;
                 camPos += -camLeft * MoveSpeed * moveX * Time.deltaTime;
                 camPos += -camDown * MoveSpeed * moveY * Time.deltaTime;
                 Camera.main.transform.position = camPos;
             }
 
             // zoom
             if (!moved && Mathf.Abs(deltaFingerValue - mOldFingerDelta) > mFingerDistanceEpsilon)
             {
                 if (deltaFingerValue - mOldFingerDelta > 0)
                 {
                     if (dist > MinDist)
                     {
                         mMoveObject.transform.Translate(-dir * ZoomSpeed * Time.deltaTime * deltaFingerValue, Space.World);
                     }
                 }
 
                 if (deltaFingerValue - mOldFingerDelta < 0)
                 {
                     if (dist < MaxDist)
                     {
                         mMoveObject.transform.Translate(dir * ZoomSpeed * Time.deltaTime * deltaFingerValue, Space.World);
                     }
                 }
             }
 
             mOldFingerDelta = deltaFingerValue;
         }
 
 
 #endif // UNITY_ANDROID || UNITY_IPHONE
 
 
 
     }
     #endregion
     ///////////////////////////////////////////////////////////////////////////
 
     ///////////////////////////////////////////////////////////////////////////
     #region Properties
     /// <summary>
     /// Gets or set value indicating if transformation is enabled
     /// </summary>
     public bool EnabledMoving
     {
         get;
         set;
     }
 
     /// <summary>
     /// Gets game object that moves around
     /// </summary>
     public Transform MoveObject
     {
         get
         {
             return mMoveObject;
         }
     }
 
     #endregion
     ///////////////////////////////////////////////////////////////////////////
 }