为unity中hololens2的默认相机写一个脚本，对空旷房间地面进行识别，开启ar后自动将ar场景放置在地面上并将长宽拉伸至真实的20m，同时固定住ar场景，这样人就可以四处移动查看ar场景的每个部分

以下是一个简单的脚本示例，可用于Unity中Hololens 2的默认相机：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.XR.WSA.Input;
using UnityEngine.XR.ARSubsystems;
using UnityEngine.XR.ARFoundation;

public class ARPlacementController : MonoBehaviour
{
    public ARRaycastManager arRaycastManager;
    public GameObject arObject;
    public float arObjectScale = 20f;

    private List<ARRaycastHit> arRaycastHits = new List<ARRaycastHit>();
    private bool isPlaced = false;

    // Start is called before the first frame update
    void Start()
    {
        // Enable the default interaction manager.
        InteractionManager interactionManager = InteractionManager.GetCurrent(null);
        if (interactionManager != null)
        {
            interactionManager.StartedPrimary += OnInteractionStarted;
        }
    }

    // Update is called once per frame
    void Update()
    {
        if (!isPlaced)
        {
            Vector3 cameraPosition = Camera.main.transform.position;
            Vector3 cameraDirection = Camera.main.transform.forward;

            if (arRaycastManager.Raycast(cameraPosition, cameraDirection, arRaycastHits, TrackableType.Planes))
            {
                Pose placementPose = arRaycastHits[0].pose;

                // Place the AR object at the detected plane and scale to real-world size.
                arObject.transform.position = placementPose.position;
                arObject.transform.rotation = placementPose.rotation;
                arObject.transform.localScale = Vector3.one * arObjectScale;

                // Lock the AR object in place.
                arObject.GetComponent<Rigidbody>().isKinematic = true;

                isPlaced = true;
            }
        }
    }

    private void OnInteractionStarted(InteractionSourceKind sourceKind)
    {
        if (isPlaced)
        {
            // Allow the AR object to be moved and rotated once it has been placed.
            arObject.GetComponent<Rigidbody>().isKinematic = false;
        }
    }
}

在这个脚本中，我们使用了AR Foundation和AR Subsystems来进行AR跟踪。首先，我们在Start()函数中启用默认的Interaction Manager，以便我们可以检测到手势输入。在Update()函数中，我们使用AR Raycast Manager来检测相机视角下的平面，并将AR场景对象放置在检测到的平面上。在放置AR场景对象后，我们锁定它的位置并将其缩放至真实的20米。一旦AR场景对象被放置并锁定，我们允许它被移动和旋转，这样人们就可以在AR场景周围自由移动了。