Unity加载OSGB倾斜摄影数据
显而易见有一个最方便的办法就是使用CesiumForUnity确定是可以通过osgb数据转换成3dtiles进行加载的，然而有没有直接加载osgb格式数据的方法呢？
我们知道osgb的osg推出的倾斜摄影数据的数据结构，所以，osg引擎一定是支持osgb最好的三维引擎，研究osgb的加载，了解osg的库也就是必然项！
然而但是，三维引擎方向，UE，Unity一定是主流中的主流了，怎么让osgb在这两个引擎中工作成了大家研究的一个侧重点。有需求才有方向嘛，不然盲人摸象。
所以，我们看看既有的成熟成果：
https://github.com/xarray/UnityOSGB.git
（git上的一个作者写好的项目，下载下来直接运行试试即可，注意下unity版本的使用）
启动项目之后示例项目挂载了ReadOSGB脚本，如下图： 
加载osgb数据取决于AsOsgbFolder，分：文件夹加载和单个osgb文件加载。
需要注意的是：文件夹加载方式并没有使用lod，所以加载的数据只是data文件夹下，瓦片文件夹下的同名osgb数据（效果如下图所示），并没有加载到层级osgb数据，显示并不尽如人意，需要自己再跟进一下（随后吧，我也没太清楚）！
文件读取的整体代码量也还好，贴出来，如下：
using System.Collections;
using System.Collections.Generic;
using System.IO;
using UnityEngine;namespace osgEx
{public class ReaderOSGB : MonoBehaviour{const int OSG_HEADER_L = 0x6C910EA1;const int OSG_HEADER_H = 0x1AFB4545;public Material _template;public string _fileOrPathName;public bool _asOsgbFolder, _withMeshCollider;public int _sceneType = 0, _version = 0;public bool _useBrackets = false;public bool _useSchemaData = false;public bool _useDomains = false;public string _currentFileName;public Plane[] _currentFrustum;public Texture2D _preloadedTexture = null;public Dictionary<uint, Object> _sharedObjects = new Dictionary<uint, Object>();public Dictionary<uint, Texture2D> _sharedTextures = new Dictionary<uint, Texture2D>();public class PagingRequest{public PagedData pagedData;public int childIndex, updatedStamp;}List<PagingRequest> _loadingRequests = new List<PagingRequest>();List<PagingRequest> _unloadingRequests = new List<PagingRequest>();Task _pagingRequestHandler;object _taskMutex = new object();bool _isTaskRunning = false;public void RequestLoadingAndUnloading(PagedData data, List<int> toLoad, List<int> toUnload){lock (_taskMutex){foreach (int index in toLoad){PagingRequest req = _loadingRequests.Find(c => c.pagedData.Equals(data) && c.childIndex.Equals(index));if (req == null){req = new PagingRequest{ pagedData = data, childIndex = index, updatedStamp = Time.frameCount };_loadingRequests.Add(req);}elsereq.updatedStamp = Time.frameCount;}foreach (int index in toUnload){PagingRequest req = _unloadingRequests.Find(c => c.pagedData.Equals(data) && c.childIndex.Equals(index));if (req == null){req = new PagingRequest{ pagedData = data, childIndex = index, updatedStamp = Time.frameCount };_unloadingRequests.Add(req);}elsereq.updatedStamp = Time.frameCount;}}}void LoadOrUnloadData(PagedData data, int index, bool toLoad){if (toLoad){string fileName = data.getFullFileName(index);GameObject fineNode = LoadSceneFromFile(fileName);if (fineNode != null){fineNode.name = Path.GetFileNameWithoutExtension(fileName);fineNode.transform.SetParent(data.gameObject.transform, false);data._pagedNodes[index] = fineNode;data._pagedNodes[0].SetActive(false); // FIXME: assume only 1 rough level}elseDebug.LogWarning("Unable to read OSGB data from " + fileName);}else{Destroy(data._pagedNodes[index]);data._pagedNodes[index] = null;data._pagedNodes[0].SetActive(true); // FIXME: assume only 1 rough level}}IEnumerator PagingTask(){_isTaskRunning = true;while (_isTaskRunning){PagedData pData0 = null;int index0 = -1, currentFrame = Time.frameCount;lock (_taskMutex){foreach (PagingRequest req in _loadingRequests){if (req.updatedStamp >= currentFrame - 1) // latest req{pData0 = req.pagedData; index0 = req.childIndex;_loadingRequests.Remove(req); break;}}if (index0 < 0){for (int i = 0; i < _loadingRequests.Count;){PagingRequest req = _loadingRequests[i];if (req.updatedStamp < currentFrame - 10) // too-old req_loadingRequests.RemoveAt(i);else ++i;}}if (_unloadingRequests.Count > 60){for (int i = 0; i < _unloadingRequests.Count;){PagingRequest req = _unloadingRequests[i];if (req.updatedStamp >= currentFrame - 1) // latest req{LoadOrUnloadData(req.pagedData, req.childIndex, false);_unloadingRequests.RemoveAt(i);}else if (req.updatedStamp < currentFrame - 10) // too-old req_unloadingRequests.RemoveAt(i);else ++i;}}}if (pData0 && index0 >= 0)LoadOrUnloadData(pData0, index0, true);//Debug.Log(_loadingRequests.Count + ", " + _unloadingRequests.Count);yield return null;}}IEnumerator StopPagingTask(Task task){_isTaskRunning = false;yield return null;task.Stop();}//加载场景数据，直接osgb文件public GameObject LoadSceneData(string fileName, BinaryReader reader){// Load header dataint magicNumL = reader.ReadInt32();int magicNumH = reader.ReadInt32();if (magicNumL != OSG_HEADER_L || magicNumH != OSG_HEADER_H){Debug.LogWarning("Unmatched magic number");return null;}_sceneType = reader.ReadInt32();_version = reader.ReadInt32();int attributes = reader.ReadInt32();Debug.Log("OSGB file " + fileName + ": version " + _version +", " + attributes.ToString("X"));_useBrackets = (attributes & 0x4) != 0;_useSchemaData = (attributes & 0x2) != 0;_useDomains = (attributes & 0x1) != 0;// TODO: handle attributesstring compressor = ObjectBase.ReadString(reader);if (compressor != "0"){Debug.LogWarning("Decompressor " + compressor + " not implemented");return null;}// Load root objectGameObject scene = new GameObject(Path.GetFileNameWithoutExtension(fileName));if (!ObjectBase.LoadObject(scene, reader, this)){Debug.LogWarning("Failed to load scene");return null;}// Clear temperatory variables_preloadedTexture = null;_sharedObjects.Clear();_sharedTextures.Clear();return scene;}//从文件中加载osgb数据 public GameObject LoadSceneFromFile(string fileName){_currentFileName = fileName;if (!File.Exists(fileName)){Debug.LogWarning("Unable to find file " + fileName);return null;}FileStream stream = File.Open(fileName, FileMode.Open, FileAccess.Read);if (!stream.CanRead){Debug.LogWarning("Unable to read binary stream from " + fileName);return null;}GameObject gameScene = LoadSceneData(fileName, new BinaryReader(stream));stream.Close(); return gameScene;}void Start(){_pagingRequestHandler = new Task(PagingTask());if (_template == null)_template = new Material(Shader.Find("Standard"));if (_asOsgbFolder){foreach (string folderName in Directory.GetDirectories(_fileOrPathName)){//只是取到了子文件夹的同名文件，lod文件没有加载，所以lod层级不足，显示效果不好string rootFile = folderName + Path.DirectorySeparatorChar+ Path.GetFileName(folderName) + ".osgb";GameObject scene = LoadSceneFromFile(rootFile);if (scene != null)scene.transform.SetParent(this.transform, false);elseDebug.LogWarning("Unable to read OSGB data from " + rootFile);}}else{GameObject scene = LoadSceneFromFile(_fileOrPathName);if (scene != null)scene.transform.SetParent(this.transform, false);elseDebug.LogWarning("Unable to read OSGB data from " + _fileOrPathName);}// Get global center & extentsMeshFilter[] mfList = GetComponentsInChildren<MeshFilter>();Bounds totalBounds = new Bounds();for (int j = 0; j < mfList.Length; ++j){Matrix4x4 l2w = mfList[j].transform.localToWorldMatrix;Vector3[] vertices = mfList[j].sharedMesh.vertices;Bounds meshBounds = new Bounds();for (int i = 0; i < vertices.Length; ++i){if (i == 0) meshBounds.center = l2w.MultiplyPoint(vertices[i]);else meshBounds.Encapsulate(l2w.MultiplyPoint(vertices[i]));}if (j == 0) totalBounds = meshBounds;else totalBounds.Encapsulate(meshBounds);}this.transform.position = -totalBounds.center;}void Update(){_currentFrustum = GeometryUtility.CalculateFrustumPlanes(Camera.main);}void OnDestroy(){StopPagingTask(_pagingRequestHandler);}}
}