C ＃ control the camera, rotate and drag the observation script (similar to scenes observation mode)

Add directly to camera , And adjust the parameters ：

Target Create an empty object separately .

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
public enum CamState
{
    Step1,
    Step2,
}
public class CameraController : MonoBehaviour
{
    public static CameraController instance;
    public Transform target; // A target object that rotates along 
    public LayerMask mask;// Select the layer to render 

    public float targetHeight = 0f; // Adjustable height 
    public float distance = 0f;// The current distance from the target object 

    public float maxDistance = 500; // The maximum distance from the target object 
    public float minDistance = 0f; // The minimum distance from the target object 

    public float xSpeed = 250.0f; //x Shaft rotation speed 
    public float ySpeed = 120.0f; //y Shaft rotation speed 

    public float yMinLimit = 15; //Y The lowest limit of the shaft 
    public float yMaxLimit = 80; //Y The highest limit of the shaft 

    public float zoomRate = 20; // Zoom speed 

    public float rotationDampening = 2.0f; // Rotation suppression 

    [HideInInspector]
    public float x = 0.0f; //x rotate 
    [HideInInspector]
    public float y = 0.0f; //Y rotate 

    private float xDampMove = 0;//X Shaft rotation jog 
    private float yDampMove = 0;//Y Shaft rotation jog 

    private float targetDistance = 0;

    bool isMove; // translation 
    public float moveSpeed = 5; // Translation speed 
    private float minSpeed = 1f; // Minimum distance used in rotation and movement algorithm 

    /// <summary>
    ///  Judge whether to execute control functions such as camera rotation and movement 
    /// </summary>
    public bool isExecutiveControl = false;


    void Awake()
    {
        instance = this;
        Vector3 angles = transform.eulerAngles;
        x = angles.y;
        y = angles.x;

        if (GetComponent<Rigidbody>())
            GetComponent<Rigidbody>().freezeRotation = true;

        targetDistance = distance;
    }
    /// <summary>
    ///  Get the currently clicked UI object 
    /// </summary>
    public bool Skode_GetCurrentSelect()
    {
        //GameObject obj = null;

        GraphicRaycaster[] graphicRaycasters = FindObjectsOfType<GraphicRaycaster>();

        PointerEventData eventData = new PointerEventData(EventSystem.current);
        eventData.pressPosition = Input.mousePosition;
        eventData.position = Input.mousePosition;
        List<RaycastResult> list = new List<RaycastResult>();

        foreach (var item in graphicRaycasters)
        {
            item.Raycast(eventData, list);
            if (list.Count > 0)
            {
                return true;
            }
        }

        return false;
    }
    void LateUpdate()
    {
        if (isExecutiveControl)
            return;

        // if (Skode_GetCurrentSelect()) {
        //     //Debug.Log("0000");
        //     return;
        // }

        if (!target)
            return;

        if (distance <= 5)
            minSpeed = 100;
        else
            minSpeed = distance;

        // Assign the rotation of the target object in real time , Pave the way for the translation function 
        target.transform.eulerAngles = new Vector3(target.transform.eulerAngles.x, transform.eulerAngles.y, target.transform.eulerAngles.z);

        if (Input.GetMouseButton(2))
        {
            // translation 
            target.transform.Translate(-Input.GetAxis("Mouse X") * 0.1f * minSpeed * moveSpeed * Time.deltaTime, 0, -Input.GetAxis("Mouse Y") * minSpeed * 0.1f * moveSpeed * Time.deltaTime);
        }


        if (Input.GetMouseButton(1))
        {
            if (!Input.GetMouseButton(2))
            {
                xDampMove = Input.GetAxis("Mouse X") * xSpeed;
                yDampMove = Input.GetAxis("Mouse Y") * ySpeed;
               
            }

        }

        xDampMove = Mathf.Clamp(xDampMove, -xSpeed, xSpeed);
        yDampMove = Mathf.Clamp(yDampMove, -ySpeed, ySpeed);

        x += xDampMove * Time.deltaTime;
        y -= yDampMove * Time.deltaTime;

        //Debug.Log("xDampMove:  " + xDampMove + "   yDampMove :  " + yDampMove);

        //if (Input.GetKey("q"))
        //    distance -= zoomRate * 0.25f * Time.deltaTime;

        //if (Input.GetKey("e"))
        //    distance += zoomRate * 0.25f * Time.deltaTime;


        distance -= (Input.GetAxis("Mouse ScrollWheel") * Time.deltaTime) * zoomRate * Mathf.Abs(minSpeed);
        //Debug.Log("targetDistance  " + distance + "    " + targetDistance);
        distance = Mathf.Clamp(distance, minDistance, maxDistance);


        targetDistance = Mathf.Lerp(targetDistance, distance, 2 * Time.deltaTime);

        //Debug.Log("targetDistance  " + distance + "    " + targetDistance);
        y = ClampAngle(y, yMinLimit, yMaxLimit);

        Quaternion rotation = Quaternion.Euler(y, x, 0);
        Vector3 position = rotation * Vector3.forward * -targetDistance + target.position + new Vector3(0, targetHeight, 0);

        xDampMove = Mathf.Lerp(xDampMove, 0, rotationDampening * Time.deltaTime);
        yDampMove = Mathf.Lerp(yDampMove, 0, rotationDampening * Time.deltaTime);


        //checkLineOfSign and Collision
        position = SignUpdate(target.position + Vector3.up * targetHeight, position, 0.3f, distance, 0.6f, mask);

        transform.rotation = rotation;
        transform.position = position;

    }

    public void chenge_dis(float dis)
    {
        if (dis > 0)
        {
            distance -= zoomRate * Time.deltaTime;
        }
        else
        {
            distance += zoomRate * Time.deltaTime;
        }

    }

    static float ClampAngle(float angle, float min, float max)
    {
        if (angle < -360)
            angle += 360;
        if (angle > 360)
            angle -= 360;
        return Mathf.Clamp(angle, min, max);
    }

    Vector3 SignUpdate(Vector3 targetPoint, Vector3 selfPosition, float checkRadios, float maxDis, float stepDis, LayerMask s_mask)
    {
        Ray ray = new Ray(targetPoint, selfPosition - targetPoint);
        RaycastHit hit;

        if (Physics.SphereCast(ray, checkRadios, out hit, maxDis, s_mask))
        {
            return ray.GetPoint(hit.distance - stepDis);
        }

        return selfPosition;
    }

    public CameraController Clone()
    {
        return new CameraController
        {
            target = target,
            targetHeight = targetHeight,
            distance = distance,
            maxDistance = maxDistance,
            minDistance = minDistance,
            xSpeed = xSpeed,
            ySpeed = ySpeed,
            yMinLimit = yMinLimit,
            yMaxLimit = yMaxLimit,
            zoomRate = zoomRate,
            rotationDampening = rotationDampening,
            moveSpeed = moveSpeed
        };
    }

    /// <summary>
    ///  Reset the viewed target coordinates and the distance between the camera and the target object , Reset camera parameters 
    /// </summary>
    /// <param name="targetTrans"></param>
    /// <param name="distance"></param>
    public void ResetData(Transform targetTrans, float distance)
    {
        //Debug.Log(" Reset parameters ");
        target = GameObject.Find("cameraTarget").transform;
        target.transform.position = targetTrans.position;
        target.transform.rotation = targetTrans.rotation;
        Vector3 angles = transform.eulerAngles;
        x = angles.y;
        y = angles.x;
        xDampMove = 0;
        yDampMove = 0;

        targetDistance = distance;
        this.distance = distance;
    }

    public void ExecutiveControlTrue()
    {
        isExecutiveControl = true;
    }

    public void ExecutiveControlFalse()
    {
        isExecutiveControl = false;
    }
}