主要介绍倾斜摄影数据OSGB二进制数据的解析，首先简单介绍一下OpenSceneGraph相关技术，并介绍倾斜摄影数据的组织结构，着重分析OSGB格式的相关字段，最后逐字节对OSGB数据进行解析并通过OpenSceneGraph对数据进行可视化，并对倾斜摄影数据的可视化进行优化。

文章目录

前言
一、OpenSceneGraph
- - 1. OSGB数据的可视化
  - 2. OSGB数据查看
  - 3.OSG文档
二、倾斜摄影数据
- - 1.数据组织结构
  - 2.OSGB格式解析
  - 3.倾斜摄影数据可视化调度优化
  - 4.多线程调试方法
总结

前言

OpenSceneGraph是一个开源的，跨平台的高性能 3D 图形工具包，它完全用标准 C++ 和 OpenGL 编写，可以用来进行三维仿真，OSG包含的多线程技术，PagedLOD技术，可以方便的处理大数据的三维模型的可视化及其调度。OSGB格式数据是OpenSceneGraph框架的自有格式，是一种二进制数据。倾斜摄影数据是以OSGB格式来组织的树形结构的数据。

一、OpenSceneGraph

1. OSGB数据的可视化

1.1 如下OSGB数据可视化部分结果：
请添加图片描述

2. OSGB数据查看

2.1 可通过OSG自带的数据转换工具osgconv将二进制的osgb数据转换为文本格式osgt、osg等，即可直接打开查看osgb数据。某文件转换后的数如下：

#Ascii Scene 
#Version 161 
#Generator OpenSceneGraph 3.6.5 
osg::PagedLOD {UniqueID 1 CenterMode USER_DEFINED_CENTER UserCenter 11406.1 -2410.49 14.3884 34.9388 RangeMode PIXEL_SIZE_ON_SCREEN RangeList 2 {0 17.4694 17.4694 1e+30 }DatabasePath TRUE "E:\\Desktop\\Data\\Tile_+154_+009/" RangeDataList 2 {"" "Tile_+154_+009_L15_0.osgb" }PriorityList 2 {0 1 0 1 }Children 1 {osg::Geode {UniqueID 2 Drawables 1 {osg::Geometry {UniqueID 3 DataVariance STATIC StateSet TRUE {osg::StateSet {UniqueID 4 DataVariance STATIC AttributeList 1 {osg::Material {UniqueID 5 Ambient TRUE Front 1 1 1 1 Back 1 1 1 1 Diffuse TRUE Front 1 1 1 1 Back 1 1 1 1 Specular TRUE Front 0 0 0 1 Back 0 0 0 1 Emission TRUE Front 0 0 0 1 Back 0 0 0 1 Shininess TRUE Front 0 Back 0 }Value OFF }TextureModeList 1 {Data 1 {GL_TEXTURE_2D ON }}TextureAttributeList 1 {Data 1 {osg::Texture2D {UniqueID 6 DataVariance STATIC WRAP_S CLAMP WRAP_T CLAMP WRAP_R CLAMP MIN_FILTER LINEAR_MIPMAP_LINEAR MAG_FILTER LINEAR UnRefImageDataAfterApply TRUE Swizzle RGBA Image TRUE {ClassName osg::Image UniqueID 7 FileName "Tile_+154_+009_0.jpg" WriteHint 2 2 DataVariance STATIC }}Value OFF }}}}PrimitiveSetList 1 {osg::DrawElementsUInt {UniqueID 8 BufferObject TRUE {osg::ElementBufferObject {UniqueID 9 Target 34963 }}Mode TRIANGLES vector 249 {0 1 2 3 4 5 6 7 8 9 10 11 6 12 7 13 14 8 14 7 12 13 8 7 15 16 17 18 14 13 19 20 21 14 18 22 23 24 22 25 26 27 28 29 30 31 23 32 14 22 33 34 25 35 36 37 38 39 27 40 33 22 24 25 27 39 22 32 23 26 39 40 41 28 30 42 43 44 26 25 45 25 34 45 34 46 45 45 47 26 48 49 50 51 52 53 53 52 54 55 56 57 54 58 53 59 60 61 62 59 61 63 62 61 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 78 77 79 80 48 50 81 82 83 78 84 85 86 87 88 76 78 85 89 90 91 81 92 82 93 94 48 72 95 96 95 97 96 93 98 94 72 99 70 95 71 100 71 95 72 101 102 95 97 95 102 91 103 104 105 102 106 107 108 109 110 82 92 111 112 113 94 98 114 106 101 97 101 106 102 71 106 97 74 73 115 116 73 88 117 118 119 82 120 83 121 108 107 104 122 91 71 105 106 123 86 88 48 80 93 91 90 103 116 115 73 73 123 88 124 119 118 120 82 125 }}}VertexArray TRUE {osg::Vec3Array {UniqueID 10 BufferObject TRUE {osg::VertexBufferObject {UniqueID 11 }}Binding BIND_PER_VERTEX vector 126 {11421.4 -2430.02 11.1509 11416 -2429.93 12.0398 11416.1 -2428.49 11.9536 11416.1 -2428.49 11.9536 11416.3 -2427.38 9.46918 11417 -2431.32 11.2052 11416 -2429.93 12.0398 11415.2 -2428.63 12.3225 11416.1 -2428.49 11.9536 11417 -2431.32 11.2052 11421.4 -2430.02 11.1509 11416.1 -2428.49 11.9536 11417 -2431.32 11.2052 11417.2 -2428.95 13.4176 11416.3 -2427.38 9.46918 11416.2 -2430.52 7.36804 11416.1 -2430.42 7.60243 11416 -2430.16 6.66749 11421.4 -2430.02 11.1509 11421.4 -2430.02 11.1509 11417.2 -2428.95 13.4176 11416 -2429.93 12.0398 11421.4 -2417.88 10.3103 11414 -2415.94 9.09115 11414.2 -2416 9.00664 11413.7 -2411.71 9.68296 11409.8 -2412.62 9.51062 11414.2 -2416 9.00664 11421.4 -2412.33 10.8725 11414.3 -2415.9 8.9807 11414.2 -2416 9.00664 11409.8 -2412.62 9.51062 11421.4 -2412.33 10.8725 11414.3 -2415.9 8.9807 11421.4 -2412.33 10.8725 11414.3 -2415.9 8.9807 11416.3 -2427.38 9.46918 11414.3 -2415.9 8.9807 11413.7 -2411.71 9.68296 11416.3 -2427.38 9.46918 11414 -2415.94 9.09115 11409.8 -2412.62 9.51062 11421.4 -2411.74 12.2718 11421.4 -2411.62 11.9188 11421.4 -2411.76 12.1873 11406.3 -2403.12 10.7203 11421.4 -2402.07 11.0026 11403 -2403.17 11.9259 11407.7 -2400.76 20.792 11408.6 -2406.5 20.017 11421.4 -2405.4 17.8293 11408.6 -2406.5 20.017 11406.3 -2403.12 10.7203 11421.4 -2405.4 17.8293 11421.4 -2402.07 11.0026 11421.4 -2402.14 14.4776 11421.4 -2402.04 14.7014 11421.4 -2402.31 14.7539 11421.4 -2399.19 11.9584 11407.7 -2400.76 20.792 11403.3 -2399.47 18.0124 11402.6 -2402.11 16.0169 11406.3 -2403.12 10.7203 11403.5 -2401.78 14.2324 11402.6 -2402.11 16.0169 11403 -2403.17 11.9259 11403.5 -2401.78 14.2324 11402.1 -2402.35 10.5813 11402 -2402.4 11.4244 11401.9 -2402.1 11.4328 11406 -2394.56 12.2159 11413.6 -2395.24 12.5957 11407 -2383.55 10.3011 11408.7 -2390.8 17.8375 11406 -2394.56 12.2159 11398.1 -2392.72 13.3419 11406.3 -2403.12 10.7203 11403.5 -2401.78 14.2324 11403.3 -2399.47 18.0124 11403 -2403.17 11.9259 11421.4 -2398.48 17.8706 11403 -2403.17 11.9259 11406 -2394.56 12.2159 11403.3 -2399.47 18.0124 11407.7 -2400.76 20.792 11413.6 -2395.24 12.5957 11421.4 -2399.19 11.9584 11421.4 -2402.07 11.0026 11417.6 -2396.89 10.3681 11421.4 -2402.07 11.0026 11421.4 -2393.37 11.0167 11417.6 -2396.89 10.3681 11406.3 -2403.12 10.7203 11408.7 -2390.8 17.8375 11407.4 -2395.19 18.3994 11419.2 -2393.09 11.0517 11421.4 -2382.84 9.16199 11421.4 -2393.37 11.0167 11398.1 -2392.72 13.3419 11398.1 -2392.72 13.3419 11419 -2393.87 10.3112 11419.8 -2394.49 10.5827 11419.5 -2394.39 10.7514 11419.8 -2394.49 10.5827 11419.2 -2393.09 11.0517 11417.6 -2396.89 10.3681 11419.5 -2394.49 10.9917 11413.6 -2395.24 12.5957 11419.5 -2394.39 10.7514 11419 -2393.87 10.3112 11413.6 -2395.24 12.5957 11419 -2393.87 10.3112 11419.5 -2394.39 10.7514 11417.6 -2396.89 10.3681 11403.3 -2399.47 18.0124 11409.7 -2395.95 16.3532 11413.6 -2395.24 12.5957 11413.6 -2395.24 12.5957 11407.7 -2400.76 20.792 11409.7 -2395.95 16.3532 11407.4 -2395.19 18.3994 11421.4 -2393.37 11.0167 11419 -2393.87 10.3112 11421.4 -2398.48 17.8706 11407.4 -2395.19 18.3994 11409.7 -2395.95 16.3532 }}}TexCoordArrayList 1 {osg::Vec2Array {UniqueID 12 BufferObject TRUE {osg::VertexBufferObject {UniqueID 11 }}Binding BIND_PER_VERTEX vector 126 {0.692426 0.855664 0.703011 0.856104 0.702753 0.861724 0.570732 0.609083 0.568671 0.599278 0.576501 0.605998 0.328366 0.857498 0.331044 0.855646 0.329737 0.852837 0.441758 0.855283 0.450283 0.850095 0.44346 0.866617 0.3252 0.858301 0.327577 0.854413 0.330703 0.845386 0.195902 0.353782 0.195705 0.354209 0.195467 0.355194 0.319499 0.845511 0.208773 0.844122 0.201316 0.85591 0.198636 0.849995 0.332787 0.808157 0.346856 0.815357 0.346555 0.815111 0.0910442 0.827874 0.0927779 0.813587 0.0994225 0.828423 0.0672952 0.362282 0.0812559 0.348427 0.0814619 0.34803 0.357319 0.814601 0.33887 0.79253 0.346497 0.814557 0.0922966 0.857352 0.0992241 0.828762 0.0720457 0.599278 0.0940807 0.599094 0.101988 0.602514 0.121655 0.836511 0.0993046 0.828032 0.0899589 0.361319 0.32333 0.364582 0.323332 0.36502 0.32333 0.36449 0.0742107 0.802832 0.0722694 0.857707 0.074282 0.793042 0.0856387 0.56386 0.0873095 0.541454 0.112424 0.545566 0.32318 0.610118 0.324436 0.572843 0.342956 0.603723 0.347425 0.576504 0.448395 0.355193 0.448395 0.355587 0.448393 0.354527 0.351276 0.579699 0.205769 0.602609 0.196975 0.591479 0.197885 0.580644 0.205193 0.561936 0.199157 0.574931 0.819516 0.855274 0.818829 0.838799 0.821246 0.848312 0.566881 0.354655 0.56682 0.35447 0.566539 0.355615 0.2075 0.556892 0.222176 0.554122 0.209448 0.599878 0.222347 0.863516 0.228093 0.838681 0.243193 0.848836 0.211664 0.318576 0.216188 0.334426 0.215268 0.351605 0.217788 0.324245 0.112475 0.572588 0.321275 0.324245 0.331548 0.338728 0.323795 0.351605 0.207751 0.356878 0.193749 0.335213 0.198898 0.820795 0.199349 0.809863 0.205922 0.824395 0.210728 0.866942 0.195963 0.854278 0.205604 0.848005 0.327399 0.318576 0.0876976 0.602792 0.0850185 0.585631 0.23329 0.56245 0.237614 0.60247 0.237531 0.561327 0.0670734 0.59545 0.192073 0.5642 0.2328 0.559397 0.234342 0.556989 0.233846 0.557384 0.199434 0.850614 0.197591 0.84838 0.230092 0.547641 0.233775 0.556984 0.333479 0.856571 0.321888 0.85038 0.322974 0.849073 0.345314 0.335213 0.824279 0.612617 0.823928 0.615871 0.817834 0.61363 0.0771236 0.568969 0.221239 0.844325 0.213566 0.835886 0.453171 0.810441 0.459564 0.852859 0.451968 0.83147 0.333637 0.358427 0.318287 0.852249 0.199158 0.846992 0.198804 0.837991 0.449074 0.842425 0.337638 0.348894 }}}}}}}
}

3.OSG文档

http://dei.isep.ipp.pt/~matos/cadeiras/cgra/OpenSceneGraphReferenceDocs/index.html

二、倾斜摄影数据

1.数据组织结构

1.1 如图，数据的组织结构如下：Data目录为数据入口目录，目录下包含很多子目录，如下，每个子目录为一个根块，每个根块是一个树形结构，是一个LOD层级结构。
请添加图片描述
1.2 每个根块下面对应很多.osgb 文件，子目录下与目录名同名的osgb文件为根文件，如下：

2.OSGB格式解析

2.1 OSGB二进制数据包含很多字段，包含OpenSceneGraph框架的非关键字段，主要用于OpenSceneGraph框架中，还包含关键字段，主要是是一个三维模型的顶点坐标，法线坐标和纹理数据，以及LOD信息。OSGB数据中包含很多不同的块(有多个字段组成)，这些块在OSGB里面存在嵌套关系，OSGB并不像一般的非嵌套关系数据，因此OSGB数据格式显得比较复杂。

下面的数据读取过程是按照读取的顺序结构组织，将其组合在一起即可读取整个OSGB格式数据。

2.2 读取OSGB文件头信息
是OSGB的头信息，低位和高位，分别为4个字节，每一个是16Bit的MD5码。

		unsigned int headerLow = 0, headerHigh = 0;fin.read((char*)&headerLow, INT_SIZE);fin.read((char*)&headerHigh, INT_SIZE);

2.3 读取后面的块，需要采用栈来辅助读取每个块。

读取文件类型:
READ_UNKNOWN=0，READ_SCENE=1，READ_IMAGE=2，READ_OBJECT=3,代表OSGB支持的类型，可以认为倾斜摄影osgb格式总是1;
读取文件版本号
读取属性:
判断文件中是否使用_useSchemaData和是否支持_SupportBinaryBrackets，全0时表示都不支持；
根据属性信息设置OSGB一些参数，后面会根据参数的设置进行信息的读取；

	//栈，读取时压入"start"_fields.push_back("Start");//读取文件类型_in->read((char*)&i, osgDB::INT_SIZE);				//unsigned int//读取文件版本号_in->read((char*)&i, osgDB::INT_SIZE);				//unsignde int//读取属性值_in->read((char*)&attributes, osgDB::INT_SIZE);		//unsignde int//根据属性值设置参数if (attributes & 0x4) _SupportBinaryBrackets = true;if (attributes & 0x2) _useSchemaData = true;//根据属性值读取信息if (attributes & 0x1){_in->read((char*)&number, osgDB::INT_SIZE);		//unsignde int//根据number值，循环读取后面的值for（unsigned int i = 0;i<number;++i）{//读取string_in->read((char*)&size, osgDB::INT_SIZE);	//int,读取string长度_in->read((char*)s.c_str(), size);			//char数组//读取int_in->read((char*)&i, osgDB::INT_SIZE);		//int,读取string长度map[s] = i;									//采用集合存储他们的信息,主要是一些版本信息}}//字段出栈_fields.pop_back();

2.4 读取压缩器的名称

	//读取压缩器名称，一般为"0"，表示压缩格式也表示压缩器名称，也可以采用zib压缩_in->read((char*)&size, osgDB::INT_SIZE);			//int,读取string长度_in->read((char*)compressorName .c_str(), size);	//char数组//根据压缩器名称进行相应的读取,我在这篇文章中主要讨论compressorName == 0的情况，对于zlib的情况，简单介绍下if (compressorName != "0"){//需要读取的数据datastd::string data;//入栈_fields.push_back("Decompression");BaseCompressor* compressor = Registry::instance()->getObjectWrapperManager()->findCompressor(compressorName);if (!compressor){throwException("InputStream: Failed to decompress stream, No such compressor.");return;}//相关读取情况主要在decompress函数里面if (!compressor->decompress(*(_in->getStream()), data))throwException("InputStream: Failed to decompress stream.");if (getException()) return;_dataDecompress = new std::stringstream(data);_in->setStream(_dataDecompress);//出栈_fields.pop_back();}

2.5 根据_useSchemaData参数读取相应信息

	if(_useSchemaData){//字段入栈_fields.push_back("SchemaData");//读取string_in->read((char*)&size, osgDB::INT_SIZE);			//int,读取string长度_in->read((char*)s.c_str(), size);					//char数组//s字符串信息解析，通过s构造一个std::istringstream对象//出栈_fields.pop_back();}

2.6 后面就存在嵌套关系，需要根据当前读取的string的值，读取对应字段的信息，每个字段里面包含有自己的读取方式。建以将每个字段元素组织成一个函数。

	//读取string_in->read((char*)&size, osgDB::INT_SIZE);				//int_in->read((char*)s.c_str(), size);						//char数组//BEGIN_BRACKET操作，根据位置和大小，用于移动读取位置；if(_supportBinaryBrackets){//当前位置入栈_beginPositions.push_back(_in->tellg());if（_in && Version > 148）{_in->read((char*)&size, osgDB::INT64_SIZE);     //unsigned long long,8字节//size入栈_blockSizes.push_back(size);}else{_in->read((char*)&size, osgDB::INT_SIZE);       //int//size入栈_blockSizes.push_back(size);}}//PROPERTY操作_in->read((char*)&value, osgDB::INT_SIZE);				//int//读取ID_in->read((char*)&id, osgDB::INT_SIZE);					//unsigned int/*说明：std::map< unsigned int, osg::ref_ptr<osg::Object> > IdentifierMap;IdentifierMap用来存储ID和ID对应的对象(块)*///判断ID对应的块是否存在IdentifierMap::iterator it = _identifierMap.find(id);if(it != _identifierMap.end()){//返回块return it->second;}//根据string className和id读取对应字段的信息osg::ref_ptr<osg::Object> obj = readObjectFields(className, id, existingObj);

2.7 根据string className的值，选择读取对应的字段。

读取osg::Object字段

	//读取string_in->read((char*)&size, osgDB::INT_SIZE);					//int_in->read((char*)s.c_str(), size);_in->read((char*)&i, osgDB::INT_SIZE);					    //int_in->read(&c, osgDB::CHAR_SIZE);							//bool

osg::Node字段

	//bool,一般读取一个char，根据char设置bool值_in->read(&c, osgDB::CHAR_SIZE);							//bool_in->read(&c, osgDB::CHAR_SIZE);							//bool_in->read(&c, osgDB::CHAR_SIZE);							//bool_in->read(&c, osgDB::CHAR_SIZE);							//bool_in->read(&c, osgDB::CHAR_SIZE);							//bool_in->read(&c, osgDB::CHAR_SIZE);							//bool_in->read((char*)&i, osgDB::INT_SIZE);						//unsignde int_in->read(&c, osgDB::CHAR_SIZE);							//bool//注意：根据前面bool的值，如果为true，还需要紧接着读取相关信息

osg::LOD字段

	_in->read((char*)&i, osgDB::INT_SIZE);						//int//bool值为false，则return true_in->read(&c, osgDB::CHAR_SIZE);							//bool//读取中心点和半径_in->read((char*)&d, osgDB::DOUBLE_SIZE);					//double_in->read((char*)&d, osgDB::DOUBLE_SIZE);					//double_in->read((char*)&d, osgDB::DOUBLE_SIZE);					//double_in->read((char*)&d, osgDB::DOUBLE_SIZE);					//double_in->read((char*)&i, osgDB::INT_SIZE);						//int//RangList信息读取_in->read(&c, osgDB::CHAR_SIZE);							//bool,false则return true_in->read((char*)&size, osgDB::INT_SIZE);					//unsignde  int//BEGIN_BRACKET操作,此处省略，见上文...//根据size大小循环读取for（int i = 0；i<size;++i){_in->read((char*)&min, osgDB::FLOAT_SIZE);				//float_in->read((char*)&max, osgDB::FLOAT_SIZE);				//float//osg::LOD& node node.setRange(i,min,max);}//END_BRACKET 操作if (_supportBinaryBrackets){//栈非空，就出栈_beginPositions.pop_back();_blockSizes.pop_back();}

osg::PagedLOD子字段

	_in->read(&c, osgDB::CHAR_SIZE);							//bool,false return true_in->read(&havePath, osgDB::CHAR_SIZE);						//bool//havePath为true，还需读取string_in->read((char*)&size, osgDB::INT_SIZE);					//int_in->read((char*)s.c_str(), size);							//string

osg::PagedLOD组合字段
读取osg::PagedLOD需要读取四个字段。
- osg::Object
- osg::Node
- osg::LOD
- osg::PagedLOD子字段
osg::Geode组合字段
- osg::Object
- osg::Node
- osg::Geode子字段
osg::Geometry组合字段
- osg::Object
- osg::Drawable
- osg::Geometry
osg::stateSet
- osg::Object
- osg::stateSet
osg::Material
- osg::Object
- osg::stateAttribute
- osg::material
osg::Texture2D
- osg::Object
- osg::stateAttribute
- osg::Texture
- osg::Texture2D
osg::Object
- osg::Object
osg::Group
- osg::Object
- osg::Node
- osg::Group
osg::DrawElementsUint
- osg::Object
- osg::PrimitiveSet
- osg::DrawElementsUint
osg::Vec3Array
- osg::Object
- osg::Array
- osg::Vec3Array
osg::Vec2Array
- osg::Object
- osg::Array
- osg::Vec2Array
osg::Node
- osg::Object
- osg::Node
osg::MatrixTransform
- osg::Object
- osg::Node
- osg::Group
- osg::Transform
- osg::MatrixTransform
osg::TexMat
- osg::Object
- osg::StateAttribute
- osg::TexMat
osg::DefaultUserData组合字段
- osg::Object
- osg::UserDataContainer
- osg::DefaultUserDataContainer
osg::DrawElementsUshort组合字段
- osg::Object
- osg::PrimitiveSet
- osg::DrawElementsUshort

2.8 完整源码解读
可以通过源码关键部分代码可以分析OSGB格式的组成。注释部分为源码摘录部分，用于辅助分析当前源码。

二进制文件OSGB写类定义：

class BinaryOutputIterator : public osgDB::OutputIterator
{
public:BinaryOutputIterator(std::ostream* ostream) { _out = ostream; }virtual ~BinaryOutputIterator() {}virtual bool isBinary() const { return true; }virtual void writeBool(bool b){char c = b ? 1 : 0; _out->write(&c, osgDB::CHAR_SIZE);}virtual void writeChar(char c){_out->write(&c, osgDB::CHAR_SIZE);}virtual void writeUChar(unsigned char c){_out->write((char*)&c, osgDB::CHAR_SIZE);}virtual void writeShort(short s){_out->write((char*)&s, osgDB::SHORT_SIZE);}virtual void writeUShort(unsigned short s){_out->write((char*)&s, osgDB::SHORT_SIZE);}virtual void writeInt(int i){_out->write((char*)&i, osgDB::INT_SIZE);}virtual void writeUInt(unsigned int i){_out->write((char*)&i, osgDB::INT_SIZE);}virtual void writeLong(long l){// On 64-bit systems a long may not be the same size as the file valueint32_t value = (int32_t)l;_out->write((char*)&value, osgDB::LONG_SIZE);}virtual void writeULong(unsigned long l){// On 64-bit systems a long may not be the same size as the file valueuint32_t value = (int32_t)l;_out->write((char*)&value, osgDB::LONG_SIZE);}virtual void writeInt64(int64_t ll){_out->write((char*)&ll, osgDB::INT64_SIZE);}virtual void writeUInt64(uint64_t ull){_out->write((char*)&ull, osgDB::INT64_SIZE);}virtual void writeInt(long long ll){_out->write((char*)&ll, osgDB::INT64_SIZE);}virtual void writeUInt(unsigned long long ull){_out->write((char*)&ull, osgDB::INT64_SIZE);}virtual void writeFloat(float f){_out->write((char*)&f, osgDB::FLOAT_SIZE);}virtual void writeDouble(double d){_out->write((char*)&d, osgDB::DOUBLE_SIZE);}virtual void writeString(const std::string& s){int size = s.size();_out->write((char*)&size, osgDB::INT_SIZE);_out->write(s.c_str(), s.size());}virtual void writeStream(std::ostream& (* /*fn*/)(std::ostream&)) {}virtual void writeBase(std::ios_base& (* /*fn*/)(std::ios_base&)) {}virtual void writeGLenum(const osgDB::ObjectGLenum& value){GLenum e = value.get(); _out->write((char*)&e, osgDB::GLENUM_SIZE);}virtual void writeProperty(const osgDB::ObjectProperty& prop){if (prop._mapProperty) _out->write((char*)&(prop._value), osgDB::INT_SIZE);}virtual void writeMark(const osgDB::ObjectMark& mark){if (_supportBinaryBrackets){if (getOutputStream() && getOutputStream()->getFileVersion() > 148){if (mark._name == "{"){uint64_t size = 0;_beginPositions.push_back(_out->tellp());_out->write((char*)&size, osgDB::INT64_SIZE);}else if (mark._name == "}" && _beginPositions.size() > 0){std::streampos pos = _out->tellp(), beginPos = _beginPositions.back();_beginPositions.pop_back();_out->seekp(beginPos);std::streampos size64 = pos - beginPos;uint64_t size = (uint64_t)size64;_out->write((char*)&size, osgDB::INT64_SIZE);_out->seekp(pos);}}else{if (mark._name == "{"){int size = 0;_beginPositions.push_back(_out->tellp());_out->write((char*)&size, osgDB::INT_SIZE);}else if (mark._name == "}" && _beginPositions.size() > 0){std::streampos pos = _out->tellp(), beginPos = _beginPositions.back();_beginPositions.pop_back();_out->seekp(beginPos);std::streampos size64 = pos - beginPos;int size = (int)size64;_out->write((char*)&size, osgDB::INT_SIZE);_out->seekp(pos);}}}}virtual void writeCharArray(const char* s, unsigned int size){if (size > 0) _out->write(s, size);}virtual void writeWrappedString(const std::string& str){writeString(str);}
protected:std::vector<std::streampos> _beginPositions;
};

二进制文件OSGB读类定义

inline void swapBytes( char* in, unsigned int size )
{char* start = in;char* end = start+size-1;while (start<end){std::swap(*start++,*end--);}
}

class BinaryInputIterator : public osgDB::InputIterator
{
public:BinaryInputIterator(std::istream* istream, int byteSwap){_in = istream;setByteSwap(byteSwap);}virtual ~BinaryInputIterator() {}virtual bool isBinary() const { return true; }virtual void readBool(bool& b){char c = 0;_in->read(&c, osgDB::CHAR_SIZE);b = (c != 0);}virtual void readChar(char& c){_in->read(&c, osgDB::CHAR_SIZE);}virtual void readSChar(signed char& c){_in->read((char*)&c, osgDB::CHAR_SIZE);}virtual void readUChar(unsigned char& c){_in->read((char*)&c, osgDB::CHAR_SIZE);}virtual void readShort(short& s){_in->read((char*)&s, osgDB::SHORT_SIZE);if (_byteSwap) osg::swapBytes((char*)&s, osgDB::SHORT_SIZE);}virtual void readUShort(unsigned short& s){_in->read((char*)&s, osgDB::SHORT_SIZE);if (_byteSwap) osg::swapBytes((char*)&s, osgDB::SHORT_SIZE);}virtual void readInt(int& i){_in->read((char*)&i, osgDB::INT_SIZE);if (_byteSwap) osg::swapBytes((char*)&i, osgDB::INT_SIZE);}virtual void readUInt(unsigned int& i){_in->read((char*)&i, osgDB::INT_SIZE);if (_byteSwap) osg::swapBytes((char*)&i, osgDB::INT_SIZE);}virtual void readLong(long& l){// On 64-bit systems a long may not be the same size as the file valueint32_t value;_in->read((char*)&value, osgDB::LONG_SIZE);if (_byteSwap) osg::swapBytes((char*)&value, osgDB::LONG_SIZE);l = (long)value;}virtual void readULong(unsigned long& l){uint32_t value;_in->read((char*)&value, osgDB::LONG_SIZE);if (_byteSwap) osg::swapBytes((char*)&value, osgDB::LONG_SIZE);l = (unsigned long)value;}virtual void readFloat(float& f){_in->read((char*)&f, osgDB::FLOAT_SIZE);if (_byteSwap) osg::swapBytes((char*)&f, osgDB::FLOAT_SIZE);}virtual void readDouble(double& d){_in->read((char*)&d, osgDB::DOUBLE_SIZE);if (_byteSwap) osg::swapBytes((char*)&d, osgDB::DOUBLE_SIZE);}virtual void readString(std::string& s){int size = 0;readInt(size);if (size > 0){s.resize(size);_in->read((char*)s.c_str(), size);}else if (size < 0){throwException("InputStream::readString() error, negative string size read.");}}virtual void readStream(std::istream& (* /*fn*/)(std::istream&)) {}virtual void readBase(std::ios_base& (* /*fn*/)(std::ios_base&)) {}virtual void readGLenum(osgDB::ObjectGLenum& value){GLenum e = 0;_in->read((char*)&e, osgDB::GLENUM_SIZE);if (_byteSwap) osg::swapBytes((char*)&e, osgDB::GLENUM_SIZE);value.set(e);}virtual void readProperty(osgDB::ObjectProperty& prop){int value = 0;if (prop._mapProperty){_in->read((char*)&value, osgDB::INT_SIZE);if (_byteSwap) osg::swapBytes((char*)&value, osgDB::INT_SIZE);}prop.set(value);}virtual void readMark(osgDB::ObjectMark& mark){if (_supportBinaryBrackets){if (mark._name == "{"){_beginPositions.push_back(_in->tellg());// since version 149 (osg version > 3.5.6) size is expressed // on 8 bytes rather than 4 bytes, // to accommodate any block size.if (getInputStream() && getInputStream()->getFileVersion() > 148){uint64_t size = 0;_in->read((char*)&size, osgDB::INT64_SIZE);if (_byteSwap) osg::swapBytes((char*)&size, osgDB::INT64_SIZE);_blockSizes.push_back(size);}else{int size = 0;_in->read((char*)&size, osgDB::INT_SIZE);if (_byteSwap) osg::swapBytes((char*)&size, osgDB::INT_SIZE);_blockSizes.push_back(size);}}else if (mark._name == "}" && _beginPositions.size() > 0){_beginPositions.pop_back();_blockSizes.pop_back();}}}virtual void readCharArray(char* s, unsigned int size){if (size > 0) _in->read(s, size);}virtual void readWrappedString(std::string& str){readString(str);}virtual void advanceToCurrentEndBracket(){if (_supportBinaryBrackets && _beginPositions.size() > 0){std::streampos position(_beginPositions.back());position += _blockSizes.back();_in->seekg(position);_beginPositions.pop_back();_blockSizes.pop_back();}}
protected:std::vector<std::streampos> _beginPositions;std::vector<std::streampos> _blockSizes;
};

读取头文件：通过倾斜摄影后缀名加载对应的读取插件

InputIterator* readInputIterator(std::istream& fin, const Options* options)
{bool extensionIsAscii = false, extensionIsXML = false;if (options){const std::string& optionString = options->getPluginStringData("fileType");if (optionString == "Ascii") extensionIsAscii = true;else if (optionString == "XML") extensionIsXML = true;}if (!extensionIsAscii && !extensionIsXML){unsigned int headerLow = 0, headerHigh = 0;fin.read((char*)&headerLow, INT_SIZE);fin.read((char*)&headerHigh, INT_SIZE);// OSG Header (MD5, 16Bit),摘录部分，定义了头信息的MD5 码//#define OSG_HEADER_LOW  0x6C910EA1//#define OSG_HEADER_HIGH 0x1AFB4545if (headerLow == OSG_HEADER_LOW && headerHigh == OSG_HEADER_HIGH){OSG_INFO << "Reading OpenSceneGraph binary file with the same endian as this computer." << std::endl;return new BinaryInputIterator(&fin, 0); // endian the same so no byte swap required}//#define OSG_REVERSE(value) ( ((value & 0x000000ff)<<24) | ((value & 0x0000ff00)<<8) | ((value & 0x00ff0000)>>8) | ((value & 0xff000000)>>24) ),摘录部分，用于辅助分析源码else if (headerLow == OSG_REVERSE(OSG_HEADER_LOW) && headerHigh == OSG_REVERSE(OSG_HEADER_HIGH)){OSG_INFO << "Reading OpenSceneGraph binary file with the different endian to this computer, doing byte swap." << std::endl;return new BinaryInputIterator(&fin, 1); // endian different so byte swap required}fin.seekg(0, std::ios::beg);}if (!extensionIsXML){std::string header; fin >> header;if (header == "#Ascii"){return new AsciiInputIterator(&fin);}fin.seekg(0, std::ios::beg);}if (1){std::string header; std::getline(fin, header);if (!header.compare(0, 5, "<?xml")){return new XmlInputIterator(&fin);}fin.seekg(0, std::ios::beg);}return NULL;
}

读取属性信息

InputStream::ReadType InputStream::start(InputIterator* inIterator)
{_fields.clear();_fields.push_back("Start");ReadType type = READ_UNKNOWN;_in = inIterator;if (!_in)throwException("InputStream: Null stream specified.");if (getException()) return type;_in->setInputStream(this);// Check OSG header informationunsigned int version = 0;if (isBinary()){unsigned int typeValue;*this >> typeValue >> version;type = static_cast<ReadType>(typeValue);unsigned int attributes; *this >> attributes;if (attributes & 0x4) inIterator->setSupportBinaryBrackets(true);if (attributes & 0x2) _useSchemaData = true;// Record custom domainsif (attributes & 0x1){unsigned int numDomains; *this >> numDomains;for (unsigned int i = 0; i < numDomains; ++i){std::string domainName; *this >> domainName;int domainVersion; *this >> domainVersion;_domainVersionMap[domainName] = domainVersion;}}}if (!isBinary()){std::string typeString; *this >> typeString;if (typeString == "Scene") type = READ_SCENE;else if (typeString == "Image") type = READ_IMAGE;else if (typeString == "Object") type = READ_OBJECT;std::string osgName, osgVersion;*this >> PROPERTY("#Version") >> version;*this >> PROPERTY("#Generator") >> osgName >> osgVersion;while (matchString("#CustomDomain")){std::string domainName; *this >> domainName;int domainVersion; *this >> domainVersion;_domainVersionMap[domainName] = domainVersion;}}// Record file version for back-compatibility checking of wrappers_fileVersion = version;_fields.pop_back();return type;
}

读取压缩器
一般压缩器名字都为0；

void InputStream::decompress()
{if (!isBinary()) return;_fields.clear();std::string compressorName; *this >> compressorName;if (compressorName != "0"){//当压缩器为zlib或其他非0压缩器时，将调用对应压缩器的decompress函数；std::string data;_fields.push_back("Decompression");//通过包装管理器查找对象包装器，读取对象的信息；BaseCompressor* compressor = Registry::instance()->getObjectWrapperManager()->findCompressor(compressorName);if (!compressor){throwException("InputStream: Failed to decompress stream, No such compressor.");return;}if (!compressor->decompress(*(_in->getStream()), data))throwException("InputStream: Failed to decompress stream.");if (getException()) return;_dataDecompress = new std::stringstream(data);_in->setStream(_dataDecompress);_fields.pop_back();}if (_useSchemaData){_fields.push_back("SchemaData");std::string schemaSource; *this >> schemaSource;std::istringstream iss(schemaSource);readSchema(iss);_fields.pop_back();}
}

null、zlib压缩器的decompress函数定义如下：

class NullCompressor : public BaseCompressor
{
public:NullCompressor() {}virtual bool compress( std::ostream& fout, const std::string& src ){int size = src.size();fout.write( (char*)&size, INT_SIZE );fout.write( src.c_str(), src.size() );return true;}virtual bool decompress( std::istream& fin, std::string& target ){int size = 0; fin.read( (char*)&size, INT_SIZE );if ( size ){target.resize( size );fin.read( (char*)target.c_str(), size );}return true;}
};
REGISTER_COMPRESSOR( "null", NullCompressor )
#ifdef USE_ZLIB
#include <zlib.h>
#define CHUNK 32768
// ZLib compressor
class ZLibCompressor : public BaseCompressor
{
public:ZLibCompressor() {}virtual bool compress( std::ostream& fout, const std::string& src ){int ret, flush = Z_FINISH;unsigned have;z_stream strm;unsigned char out[CHUNK];int level = 6;int stategy = Z_DEFAULT_STRATEGY;/* allocate deflate state */strm.zalloc = Z_NULL;strm.zfree = Z_NULL;strm.opaque = Z_NULL;ret = deflateInit2( &strm, level, Z_DEFLATED, 15+16, // +16 to use gzip encoding8, // defaultstategy );if ( ret != Z_OK ) return false;strm.avail_in = src.size();strm.next_in = (Bytef*)( &(*src.begin()) );/* run deflate() on input until output buffer not full, finishcompression if all of source has been read in */do{strm.avail_out = CHUNK;strm.next_out = out;ret = deflate(&strm, flush);    /* no bad return value */if ( ret == Z_STREAM_ERROR ){OSG_NOTICE << "Z_STREAM_ERROR" << std::endl;return false;}have = CHUNK - strm.avail_out;if ( have>0 ) fout.write( (const char*)out, have );if ( fout.fail() ){(void)deflateEnd( &strm );return false;}} while ( strm.avail_out==0 );/* clean up and return */(void)deflateEnd( &strm );return true;}virtual bool decompress( std::istream& fin, std::string& target ){int ret;unsigned have;z_stream strm;unsigned char in[CHUNK];unsigned char out[CHUNK];/* allocate inflate state */strm.zalloc = Z_NULL;strm.zfree = Z_NULL;strm.opaque = Z_NULL;strm.avail_in = 0;strm.next_in = Z_NULL;ret = inflateInit2( &strm,15 + 32 ); // autodected zlib or gzip headerif ( ret!=Z_OK ){OSG_INFO << "failed to init" << std::endl;return ret!=0;}/* decompress until deflate stream ends or end of file */do{fin.read( (char *)in, CHUNK );strm.avail_in = fin.gcount();if (strm.avail_in==0 ) break;/* run inflate() on input until output buffer not full */strm.next_in = in;do{strm.avail_out = CHUNK;strm.next_out = out;ret = inflate( &strm, Z_NO_FLUSH );switch (ret){case Z_NEED_DICT:case Z_DATA_ERROR:case Z_MEM_ERROR:(void)inflateEnd( &strm );return false;}have = CHUNK - strm.avail_out;target.append( (char*)out, have );} while ( strm.avail_out==0 );/* done when inflate() says it's done */} while ( ret!=Z_STREAM_END );/* clean up and return */(void)inflateEnd( &strm );return ret==Z_STREAM_END ? true : false;}
};
REGISTER_COMPRESSOR( "zlib", ZLibCompressor )
#endif

读取每个对象
根据每个组合对象的名称，读取其子对象。

osg::ref_ptr<osg::Object> InputStream::readObject(osg::Object* existingObj)
{std::string className;unsigned int id = 0;*this >> className;if (className == "NULL"){return 0;}*this >> BEGIN_BRACKET >> PROPERTY("UniqueID") >> id;if (getException()) return 0;//每个对象对应一个id和名字，根据id可以判断该id是否已经存在；IdentifierMap::iterator itr = _identifierMap.find(id);if (itr != _identifierMap.end()){advanceToCurrentEndBracket();return itr->second;}std::cout << "className = " << className << std::endl;osg::ref_ptr<osg::Object> obj = readObjectFields(className, id, existingObj);advanceToCurrentEndBracket();return obj;
}

BEGIN_BRACKET 和END_BRACKET 操作
BEGIN_BRACKET 、END_BRACKET 为ObjectMark类对象，不同的对象设置了不同的初始值。
- 类定义

	class ObjectMark{public:ObjectMark() : _indentDelta(0) {}ObjectMark(const ObjectMark& copy): _name(copy._name), _indentDelta(copy._indentDelta) {}void set(const char* name, int delta = 0){_name = name; _indentDelta = delta;}std::string _name;int _indentDelta;};

BEGIN_BRACKET 操作
BEGIN_BRACKET 是ObjectMark对象，设定了对象的初始值："{"

	virtual void readMark(osgDB::ObjectMark& mark){if (_supportBinaryBrackets){if (mark._name == "{"){_beginPositions.push_back(_in->tellg());// since version 149 (osg version > 3.5.6) size is expressed // on 8 bytes rather than 4 bytes, // to accommodate any block size.if (getInputStream() && getInputStream()->getFileVersion() > 148){uint64_t size = 0;_in->read((char*)&size, osgDB::INT64_SIZE);if (_byteSwap) osg::swapBytes((char*)&size, osgDB::INT64_SIZE);_blockSizes.push_back(size);}else{int size = 0;_in->read((char*)&size, osgDB::INT_SIZE);if (_byteSwap) osg::swapBytes((char*)&size, osgDB::INT_SIZE);_blockSizes.push_back(size);}}else if (mark._name == "}" && _beginPositions.size() > 0){_beginPositions.pop_back();_blockSizes.pop_back();}}}

PROPERTY操作
- 类定义

	class ObjectProperty{public:ObjectProperty() : _value(0), _mapProperty(false) {}ObjectProperty(const char* name, int value = 0, bool useMap = false): _name(name), _value(value), _mapProperty(useMap) {}ObjectProperty(const ObjectProperty& copy): _name(copy._name), _value(copy._value), _mapProperty(copy._mapProperty) {}ObjectProperty& operator()(const char* name){_name = name; return *this;}void set(int v) { _value = v; }int get() const { return _value; }std::string _name;int _value;bool _mapProperty;};

读取操作

	virtual void readProperty(osgDB::ObjectProperty& prop){int value = 0;if (prop._mapProperty){_in->read((char*)&value, osgDB::INT_SIZE);if (_byteSwap) osg::swapBytes((char*)&value, osgDB::INT_SIZE);}prop.set(value);}

子字段读取
代码中getObjectWrapperManager()->findWrapper(className)通过查找对象的包装器，每种包装器中封装了其子字段，通过getAssociates()获取到包装器的子字段，然后逐一读取。

osg::ref_ptr<osg::Object> InputStream::readObjectFields(const std::string& className, unsigned int id, osg::Object* existingObj)
{ObjectWrapper* wrapper = Registry::instance()->getObjectWrapperManager()->findWrapper(className);if (!wrapper){OSG_WARN << "InputStream::readObject(): Unsupported wrapper class "<< className << std::endl;return NULL;}int inputVersion = getFileVersion(wrapper->getDomain());osg::ref_ptr<osg::Object> obj = existingObj ? existingObj : wrapper->createInstance();_identifierMap[id] = obj;if (obj.valid()){const ObjectWrapper::RevisionAssociateList& associates = wrapper->getAssociates();for (ObjectWrapper::RevisionAssociateList::const_iterator itr = associates.begin(); itr != associates.end(); ++itr){if (itr->_firstVersion <= inputVersion &&inputVersion <= itr->_lastVersion){ObjectWrapper* assocWrapper = Registry::instance()->getObjectWrapperManager()->findWrapper(itr->_name);if (!assocWrapper){OSG_WARN << "InputStream::readObject(): Unsupported associated class "<< itr->_name << std::endl;continue;}_fields.push_back(assocWrapper->getName());std::cout << "_fileds add : " << assocWrapper->getName() << std::endl;assocWrapper->read(*this, *obj);if (getException()) return NULL;_fields.pop_back();}else{/* OSG_INFO << "InputStream::readObject():"<<className<<" Ignoring associated class due to version mismatch"<< itr->_name<<"["<<itr->_firstVersion <<","<<itr->_lastVersion <<"]for version "<<inputVersion<< std::endl;*/}}}return obj;
}

查找包装器函数如下：

ObjectWrapper* ObjectWrapperManager::findWrapper( const std::string& name )
{OpenThreads::ScopedLock<OpenThreads::ReentrantMutex> lock(_wrapperMutex);WrapperMap::iterator itr = _wrappers.find( name );if ( itr!=_wrappers.end() ) return itr->second.get();// Load external librariesstd::string::size_type posDoubleColon = name.rfind("::");if ( posDoubleColon!=std::string::npos ){std::string libName = std::string( name, 0, posDoubleColon );ObjectWrapper* found=0;std::string nodeKitLib = osgDB::Registry::instance()->createLibraryNameForNodeKit(libName);if ( osgDB::Registry::instance()->loadLibrary(nodeKitLib)==osgDB::Registry::LOADED )found= findWrapper(name);std::string pluginLib = osgDB::Registry::instance()->createLibraryNameForExtension(std::string("serializers_")+libName);if ( osgDB::Registry::instance()->loadLibrary(pluginLib)==osgDB::Registry::LOADED )found= findWrapper(name);pluginLib = osgDB::Registry::instance()->createLibraryNameForExtension(libName);if ( osgDB::Registry::instance()->loadLibrary(pluginLib)==osgDB::Registry::LOADED )found= findWrapper(name);if (found) found->setupAssociatesRevisionsInheritanceIfRequired();return found;}return NULL;
}

包装器子字段读取函数如下：通过对应的序列化函数读取相应的信息，序列化函数负责读取信息，

bool ObjectWrapper::read( InputStream& is, osg::Object& obj )
{bool readOK = true;int inputVersion = is.getFileVersion(_domain);for ( SerializerList::iterator itr=_serializers.begin(); itr!=_serializers.end(); ++itr ){BaseSerializer* serializer = itr->get();if ( serializer->_firstVersion <= inputVersion && inputVersion <= serializer->_lastVersion && serializer->supportsReadWrite()){if ( !serializer->read(is, obj) ){OSG_WARN << "ObjectWrapper::read(): Error reading property "<< _name << "::" << (*itr)->getName() << std::endl;readOK = false;}}else{// OSG_NOTICE<<"Ignoring serializer due to version mismatch"<<std::endl;}}for ( FinishedObjectReadCallbackList::iterator itr=_finishedObjectReadCallbacks.begin();itr!=_finishedObjectReadCallbacks.end();++itr ){(*itr)->objectRead(is, obj);}return readOK;
}

2.8 序列化机制

每种对象对应一个序列化机制，下面通过PagedLOD介绍其序列化机制。

#include <osg/PagedLOD>
#include <osgDB/ObjectWrapper>
#include <osgDB/InputStream>
#include <osgDB/OutputStream>
#include <osgDB/Options>
// _databasePath
static bool checkDatabasePath( const osg::PagedLOD& node )
{return true;
}
static bool readDatabasePath( osgDB::InputStream& is, osg::PagedLOD& node )
{bool hasPath; is >> hasPath;if ( !hasPath ){if ( is.getOptions() && !is.getOptions()->getDatabasePathList().empty() ){const std::string& optionPath = is.getOptions()->getDatabasePathList().front();if ( !optionPath.empty() ) node.setDatabasePath( optionPath );}}else{std::string path; is.readWrappedString( path );node.setDatabasePath( path );}return true;
}
static bool writeDatabasePath( osgDB::OutputStream& os, const osg::PagedLOD& node )
{os << (!node.getDatabasePath().empty());if ( !node.getDatabasePath().empty() )os.writeWrappedString( node.getDatabasePath() );os << std::endl;return true;
}
// _perRangeDataList
static bool checkRangeDataList( const osg::PagedLOD& node )
{return node.getNumFileNames()>0;
}
static bool readRangeDataList( osgDB::InputStream& is, osg::PagedLOD& node )
{unsigned int size = 0; is >> size >> is.BEGIN_BRACKET;for ( unsigned int i=0; i<size; ++i ){std::string name; is.readWrappedString( name );node.setFileName( i, name );}is >> is.END_BRACKET;size = 0; is >> is.PROPERTY("PriorityList") >> size >> is.BEGIN_BRACKET;for ( unsigned int i=0; i<size; ++i ){float offset, scale;is >> offset >> scale;node.setPriorityOffset( i, offset );node.setPriorityScale( i, scale );}is >> is.END_BRACKET;return true;
}
static bool writeRangeDataList( osgDB::OutputStream& os, const osg::PagedLOD& node )
{unsigned int size = node.getNumFileNames();os << size << os.BEGIN_BRACKET << std::endl;for ( unsigned int i=0; i<size; ++i ){os.writeWrappedString( node.getFileName(i) );os << std::endl;}os << os.END_BRACKET << std::endl;size = node.getNumPriorityOffsets();os << os.PROPERTY("PriorityList") << size << os.BEGIN_BRACKET << std::endl;for ( unsigned int i=0; i<size; ++i ){os << node.getPriorityOffset(i) << node.getPriorityScale(i) << std::endl;}os << os.END_BRACKET << std::endl;return true;
}
// _children
static bool checkChildren( const osg::PagedLOD& node )
{return node.getNumChildren()>0;
}
static bool readChildren( osgDB::InputStream& is, osg::PagedLOD& node )
{unsigned int size = 0; is >> size;if (size > 0){is >> is.BEGIN_BRACKET;for ( unsigned int i=0; i<size; ++i ){osg::ref_ptr<osg::Node> child = is.readObjectOfType<osg::Node>();if ( child ) node.addChild( child );}is >> is.END_BRACKET;}return true;
}
static bool writeChildren( osgDB::OutputStream& os, const osg::PagedLOD& node )
{unsigned int size=node.getNumFileNames(), dynamicLoadedSize=0;for ( unsigned int i=0; i<size; ++i ){if ( !node.getFileName(i).empty() )dynamicLoadedSize++;}unsigned int realSize = size-dynamicLoadedSize; os << realSize;if ( realSize>0 ){os << os.BEGIN_BRACKET << std::endl;for ( unsigned int i=0; i<size; ++i ){if ( !node.getFileName(i).empty() ) continue;if ( i<node.getNumChildren() )os << node.getChild(i);}os << os.END_BRACKET;}os << std::endl;return true;
}
//封装对应的子字段名称
REGISTER_OBJECT_WRAPPER( PagedLOD,new osg::PagedLOD,osg::PagedLOD,"osg::Object osg::Node osg::LOD osg::PagedLOD" )
{// Note: osg::Group is not in the list to prevent recording dynamic loaded childrenADD_USER_SERIALIZER( DatabasePath );  // _databasePathADD_UINT_SERIALIZER( FrameNumberOfLastTraversal, 0 );  // _frameNumberOfLastTraversal, note, not required, removed from soversion 70 onwwards, see belowADD_UINT_SERIALIZER( NumChildrenThatCannotBeExpired, 0 );  // _numChildrenThatCannotBeExpiredADD_BOOL_SERIALIZER( DisableExternalChildrenPaging, false );  // _disableExternalChildrenPagingADD_USER_SERIALIZER( RangeDataList );  // _perRangeDataListADD_USER_SERIALIZER( Children );  // _children (which are not loaded from external){UPDATE_TO_VERSION_SCOPED( 70 )REMOVE_SERIALIZER( FrameNumberOfLastTraversal );}
}

至此，对osgb格式有了基本的了解，但需要能解析其数据，还需要分析其他对象的序列化机制，因为涉及到迭代版本的兼容等问题，因此可以直接将OSG源码中的读写源码抽出来作为项目的一部分，就能很好的解决版本兼容问题。

3.倾斜摄影数据可视化调度优化

3.1 加载单个osgb文件并显示

	osg::Group* root = new osg::Group;//读取文件osg::ref_ptr<osg::Node> n = osgDB::readNodeFile("E:/Desktop/Data/Tile_+157_+009/Tile_+157_+009.osgb");root->addChild(n);osg::ref_ptr<osgViewer::Viewer> viewer = new osgViewer::Viewer;viewer->setSceneData(root);viewer->setUpViewInWindow(20, 20, 1400, 700);//相应常见的键盘按键功能viewer->addEventHandler(new osgGA::StateSetManipulator(viewer->getCamera()->getOrCreateStateSet()));viewer->addEventHandler(new osgViewer::WindowSizeHandler);viewer->addEventHandler(new osgViewer::StatsHandler);viewer->realize();return viewer->run();