[原][osgearth]API加载earth文件的解析

参考：http://blog.csdn.net/cccstudyer/article/details/17691893

通过srcosgEarthDriversearthReaderWriterOsgEarth.cpp文件

ReaderWriterEarth类，用来解析“earth”文件

在文件225行的readNode函数

 1   virtual ReadResult readNode(std::istream& in, const osgDB::Options* readOptions) const
 2         {
 3             // pull the URI context from the options structure (since we're reading
 4             // from an "anonymous" stream here)
 5             URIContext uriContext( readOptions ); 
 6 
 7             osg::ref_ptr<XmlDocument> doc = XmlDocument::load( in, uriContext );
 8             if ( !doc.valid() )
 9                 return ReadResult::ERROR_IN_READING_FILE;
10 
11             Config docConf = doc->getConfig();
12 
13             // support both "map" and "earth" tag names at the top level
14             Config conf;
15             if ( docConf.hasChild( "map" ) )
16                 conf = docConf.child( "map" );
17             else if ( docConf.hasChild( "earth" ) )
18                 conf = docConf.child( "earth" );
19 
20             osg::ref_ptr<osg::Node> node;
21 
22             if ( !conf.empty() )
23             {
24                 // see if we were given a reference URI to use:
25                 std::string refURI = uriContext.referrer();
26 
27                 if ( conf.value("version") == "1" )
28                 {
29                     OE_INFO << LC << "Detected a version 1.x earth file" << std::endl;
30                     EarthFileSerializer1 ser;
31                     node = ser.deserialize( conf, refURI );
32                 }
33 
34                 else
35                 {
36                     if ( conf.value("version") != "2" )
37                         OE_DEBUG << LC << "No valid earth file version; assuming version='2'" << std::endl;
38 
39                     // attempt to parse a "default options" JSON string:
40                     std::string defaultConfStr;
41                     if ( readOptions )
42                     {
43                         defaultConfStr = readOptions->getPluginStringData("osgEarth.defaultOptions");
44                         if ( !defaultConfStr.empty() )
45                         {
46                             Config optionsConf("options");
47                             if (optionsConf.fromJSON(defaultConfStr))
48                             {
49                                 //OE_NOTICE << "

Original = 
" << conf.toJSON(true) << "
";
50                                 Config* original = conf.mutable_child("options");
51                                 if ( original )
52                                 {
53                                     recursiveUniqueKeyMerge(optionsConf, *original);
54                                 }
55                                 if ( !optionsConf.empty() )
56                                 {
57                                     conf.set("options", optionsConf);
58                                 }
59                                 //OE_NOTICE << "

Merged = 
" << conf.toJSON(true) << "
";
60                             }
61                         }
62                     }
63 
64                     EarthFileSerializer2 ser;
65                     node = ser.deserialize( conf, refURI );
66                 }
67             }
68 
69             MapNode* mapNode = MapNode::get(node.get());
70             if (mapNode)
71             {
72                 // If the user passed in a cache object, apply it to the map now
73                 CacheSettings* cacheSettings = CacheSettings::get(readOptions);
74                 if (cacheSettings && cacheSettings->getCache())
75                 {
76                     mapNode->getMap()->setCache( cacheSettings->getCache() );
77                     OE_INFO << LC << "Applied user-supplied cache to the Map
";
78                 }
79             }
80 
81             return ReadResult(node.get());
82         }
83 };

看到65行的读取调用

进入srcosgEarthDriversearthEarthFileSerializer2.cpp文件

EarthFileSerializer2类的deserialize函数

  1  void addImageLayer(const Config& conf, Map* map)
  2     {
  3         ImageLayerOptions options( conf );
  4         options.name() = conf.value("name");
  5         ImageLayer* layer = new ImageLayer(options);
  6         map->addLayer(layer);
  7         if (layer->getStatus().isError())
  8             OE_WARN << LC << "Layer "" << layer->getName() << "" : " << layer->getStatus().toString() << std::endl;
  9     }
 10 
 11     void addElevationLayer(const Config& conf, Map* map)
 12     {
 13         ElevationLayerOptions options( conf );
 14         options.name() = conf.value( "name" );
 15         ElevationLayer* layer = new ElevationLayer(options);
 16         map->addLayer(layer);
 17         if (layer->getStatus().isError())
 18             OE_WARN << LC << "Layer "" << layer->getName() << "" : " << layer->getStatus().toString() << std::endl;
 19     }
 20 
 21     void addModelLayer(const Config& conf, Map* map)
 22     {
 23         ModelLayerOptions options( conf );
 24         options.name() = conf.value( "name" );
 25         options.driver() = ModelSourceOptions( conf );
 26         ModelLayer* layer = new ModelLayer(options);
 27         map->addLayer(layer);
 28         if (layer->getStatus().isError())
 29             OE_WARN << LC << "Layer "" << layer->getName() << "" : " << layer->getStatus().toString() << std::endl;
 30     }
 31 
 32     void addMaskLayer(const Config& conf, Map* map)
 33     {
 34         MaskLayerOptions options(conf);
 35         options.name() = conf.value( "name" );
 36         options.driver() = MaskSourceOptions(options);
 37         MaskLayer* layer = new MaskLayer(options);
 38         map->addLayer(layer);
 39         if (layer->getStatus().isError())
 40             OE_WARN << LC << "Layer "" << layer->getName() << "" : " << layer->getStatus().toString() << std::endl;
 41     }
 42 
 43     // support for "special" extension names (convenience and backwards compat)
 44     Extension* createSpecialExtension(const Config& conf)
 45     {
 46         // special support for the default sky extension:
 47         if (conf.key() == "sky" && !conf.hasValue("driver"))
 48             return Extension::create("sky_simple", conf);
 49 
 50         if (conf.key() == "ocean" && !conf.hasValue("driver"))
 51             return Extension::create("ocean_simple", conf);
 52 
 53         return 0L;
 54     }
 55 
 56     bool addLayer(const Config& conf, Map* map)
 57     {
 58         std::string name = conf.key();
 59         Layer* layer = Layer::create(name, conf);
 60         if (layer)
 61         {
 62             map->addLayer(layer);
 63             if (layer->getStatus().isError())
 64                 OE_WARN << LC << "Layer "" << layer->getName() << "" : " << layer->getStatus().toString() << std::endl;
 65         }
 66         return layer != 0L;
 67     }
 68 
 69 osg::Node*
 70 EarthFileSerializer2::deserialize( const Config& conf, const std::string& referrer ) const
 71 {
 72     // First, pre-load any extension DLLs.
 73     preloadExtensionLibs(conf);
 74     preloadExtensionLibs(conf.child("extensions"));
 75     preloadExtensionLibs(conf.child("external"));
 76 
 77     MapOptions mapOptions( conf.child( "options" ) );
 78 
 79     // legacy: check for name/type in top-level attrs:
 80     if ( conf.hasValue( "name" ) || conf.hasValue( "type" ) )
 81     {
 82         Config legacy;
 83         if ( conf.hasValue("name") ) legacy.add( "name", conf.value("name") );
 84         if ( conf.hasValue("type") ) legacy.add( "type", conf.value("type") );
 85         mapOptions.mergeConfig( legacy );
 86     }
 87 
 88     Map* map = new Map( mapOptions );
 89 
 90     // Start a batch update of the map:
 91     map->beginUpdate();
 92 
 93     // Read all the elevation layers in FIRST so other layers can access them for things like clamping.
 94     for(ConfigSet::const_iterator i = conf.children().begin(); i != conf.children().end(); ++i)
 95     {
 96         if ( i->key() == "elevation" || i->key() == "heightfield" )
 97         {
 98             addElevationLayer( *i, map );
 99         }
100     }
101 
102     Config externalConfig;
103     std::vector<osg::ref_ptr<Extension> > extensions;
104 
105     // Read the layers in LAST (otherwise they will not benefit from the cache/profile configuration)
106     for(ConfigSet::const_iterator i = conf.children().begin(); i != conf.children().end(); ++i)
107     {
108         if (i->key() == "options" || i->key() == "name" || i->key() == "type" || i->key() == "version")
109         {
110             // nop - handled earlier
111         }
112 
113         else if ( i->key() == "image" )
114         {
115             addImageLayer( *i, map );
116         }
117 
118         else if ( i->key() == "model" )
119         {
120             addModelLayer( *i, map );
121         }
122 
123         else if ( i->key() == "mask" )
124         {
125             addMaskLayer( *i, map );
126         }
127 
128         else if ( i->key() == "external" || i->key() == "extensions" )
129         {
130             externalConfig = *i;
131             
132             for(ConfigSet::const_iterator e = i->children().begin(); e != i->children().end(); ++e)
133             {
134                 Extension* extension = loadExtension(*e);
135                 if (extension)
136                     extensions.push_back(extension);
137                 //addExtension( *e, mapNode.get() );
138             }
139         }
140 
141         else if ( !isReservedWord(i->key()) ) // plugins/extensions.
142         {
143             bool addedLayer = addLayer(*i, map); //mapNode.get());
144 
145             if ( !addedLayer )
146             {
147                 Extension* extension = loadExtension(*i);
148                 if (extension)
149                     extensions.push_back(extension);
150                 //OE_INFO << LC << "Tried to load "" << i->key() << "" as a layer; now trying extension
";
151                 //addExtension( *i, mapNode.get() );
152             }
153         }
154     }
155 
156     // Complete the batch update of the map
157     map->endUpdate();
158 
159     // Yes, MapOptions and MapNodeOptions share the same Config node. Weird but true.
160     MapNodeOptions mapNodeOptions( conf.child("options") );
161 
162     // Create a map node.
163     osg::ref_ptr<MapNode> mapNode = new MapNode( map, mapNodeOptions );
164 
165     // Apply the external conf if there is one.
166     if (!externalConfig.empty())
167     {
168         mapNode->externalConfig() = externalConfig;
169     }
170 
171     // Install the extensions
172     for (unsigned i = 0; i < extensions.size(); ++i)
173     {
174         mapNode->addExtension(extensions.at(i).get());
175     }
176 
177     // return the topmost parent of the mapnode. It's possible that
178     // an extension added parents!
179     osg::Node* top = mapNode.release();
180 
181     while( top->getNumParents() > 0 )
182         top = top->getParent(0);
183 
184     return top;
185 }

从上面可以看到

1 earth插件 map 统筹OE中所有"层"的概念，支持多层影像，高程，模型，镂空层（mask）等

2各个层相应配置的属性由指定的Option类从Config中获取，如果对应Config中有Option类指定元素相应值的配置Option将其写入

为了统筹OE各个层的属性配置，OE提供了ConfigOptions类，ConfigOptions类就是对某个Config类的封装，提供了到Config层次上的调用，例如Config赋值，拼接等

为不同层的属性配置提供了存储载体,结合上文map包含的图层有以下关系

通过这些类，可以很方便的将特定的XML节点下属性配置生成Config归类到某一个图层中，以下列出部分图层的属性(仅供参考)

MapOptions：XML<<options>>节点下配置的信息，主要是配置地形渲染时的属性；包括如下

<elevation_interploation> 插值，nearset 最近点插值 average 最近点平均值 bilinear 线性插值， triangulate 三角面片插值
<elevation_tile_size> 瓦片大小
<elevation_texture_size> 纹理大小
<overlay_wapring> 纹理装载
<overlay_blending>混合
<overlay_minmapping> 纹理映射
<overlay_texture_size>
<overlay_attach_stencil>模板

ImageLayerOptions： XML<<image>>节点下配置的信息，很明显，影像属性配置，部分属性值

<nodata_image> 无数据显示的url
<opacity> 透明度
<min_range> 最小可视范围
<max_range> 最大可视范围
<min_level> 最小显示细节层级
<max_level> 最大显示细节层级
<min_resolution> 数据的最小分辨率，单位的像素
<max_resolution>数据的最大分辨率，单位的像素
<enable> 是否包含进map层
<visible> 可视

ElevationLayerOptions： XML<<elevation>>or<<heightfield>>节点下配置的信息，高程层

<min_level> 最小显示细节层级
<max_level> 最大显示细节层级
<min_resolution> 数据的最小分辨率，单位的像素
<max_resolution>数据的最大分辨率，单位的像素
<enable> 是否包含进map层

ModelLayerOptions： XML<<Model>>节点下配置的信息模型层装载矢量数据，模型，几何体等

<name>
<driver>
<enable><span style="font-family:Arial, Helvetica, sans-serif;">是否包含进map层</span>
<visible>是否可见
<overLay>

MaskLayerOptions： XML<<mask>>节点配置下的信息，镂空层

一个比较特殊的节点 ext(Config); 暂且叫他功能层，XML <<external>>,它由mapNode直接读取配置信息，实现一些经常用到的功能点，例如视点定位 <<<viewpoint>> 星空时刻设置<<sky>>等