osgEarth使用笔记4——加载矢量数据
目录
1. 概述
前面文章加载的底图数据是一种栅格数据，还有一种很重要的地理信息表现形式是矢量数据。在osgEarth中，这部分包含的内容还是很丰富的，这里就总结一二。
2. 详论
2.1. 基本绘制
在《osgEarth使用笔记1——显示一个数字地球》这篇文章中代码的基础之上，添加加载显示矢量的代码：
#include <Windows.h> #include <iostream> #include <string> #include <osgViewer/Viewer> #include <osgDB/ReadFile> #include <osgEarth/MapNode> #include <osgEarth/ImageLayer> #include <osgEarthDrivers/gdal/GDALOptions> #include <osgEarthDrivers/cache_filesystem/FileSystemCache> #include <osgEarthDrivers/feature_ogr/OGRFeatureOptions> #include <osgEarthFeatures/FeatureSourceLayer> #include <osgEarthFeatures/FeatureModelLayer> #include <osgEarthUtil/EarthManipulator> using namespace std; void AddVector(osg::ref_ptr<osgEarth::Map> map) { // std::string filePath = "D:/Work/OSGNewBuild/osgearth-2.10.1/data/world.shp"; osgEarth::Drivers::OGRFeatureOptions featureData; featureData.url() = filePath; // 如果缺少空间参考，可以手动指定 // ifstream infile("C:/Data/vector/hs/23.prj"); // string line; // getline(infile, line); // featureData.profile()->srsString() = line; // Make a feature source layer and add it to the Map: osgEarth::Features::FeatureSourceLayerOptions ogrLayer; ogrLayer.name() = filePath + "_source"; ogrLayer.featureSource() = featureData; osgEarth::Features::FeatureSourceLayer* featureSourceLayer = new osgEarth::Features::FeatureSourceLayer(ogrLayer); map->addLayer(featureSourceLayer); osgEarth::Features::FeatureSource *features = featureSourceLayer->getFeatureSource(); if (!features) { printf(("无法打开该矢量文件！")); return; } // osgEarth::Features::FeatureModelLayerOptions fmlOpt; fmlOpt.name() = filePath; fmlOpt.featureSourceLayer() = filePath + "_source"; fmlOpt.enableLighting() = false; osg::ref_ptr<osgEarth::Features::FeatureModelLayer> fml = new osgEarth::Features::FeatureModelLayer(fmlOpt); map->addLayer(fml); } int main() { osgEarth::ProfileOptions profileOpts; //地图配置：设置缓存目录 osgEarth::Drivers::FileSystemCacheOptions cacheOpts; string cacheDir = "D:/Work/OSGNewBuild/tmp"; cacheOpts.rootPath() = cacheDir; // osgEarth::MapOptions mapOpts; mapOpts.cache() = cacheOpts; mapOpts.profile() = profileOpts; //创建地图节点 osg::ref_ptr<osgEarth::Map> map = new osgEarth::Map(mapOpts); osg::ref_ptr<osgEarth::MapNode> mapNode = new osgEarth::MapNode(map); osgEarth::Drivers::GDALOptions gdal; gdal.url() = "D:/Work/OSGNewBuild/osgearth-2.10.1/data/world.tif"; osg::ref_ptr<osgEarth::ImageLayer> layer = new osgEarth::ImageLayer("BlueMarble", gdal); map->addLayer(layer); AddVector(map); osgViewer::Viewer viewer; viewer.setSceneData(mapNode); osg::ref_ptr< osgEarth::Util::EarthManipulator> mainManipulator = new osgEarth::Util::EarthManipulator; viewer.setCameraManipulator(mainManipulator); viewer.setUpViewInWindow(100, 100, 800, 600); return viewer.run(); }
osgEarth表达矢量的基本思路是，先将其读取到矢量源图层FeatureSourceLayer中，这个图层加载到osgEarth的图层列表中是不显示的，必须得再加载一个专门的符号化图层，将其符号号，才能正常显示。这里使用的是FeatureModelLayer，也就是将这个矢量当成模型来加载。运行这段程序显示结果如下：
这个矢量加载的是osgEarth自带的矢量地图world.shp，是一个面矢量，但是显示的效果却不太正确，也是因为没有设置合适的符号化方式。
2.2. 矢量符号化
矢量符号化在osgEarth中被抽象成了类似于CSS中样式表StyleSheet，可以在其中加载样式Style：
//设置样式 osgEarth::Symbology::Style style; //具体设置 //... // osgEarth::Features::FeatureModelLayerOptions fmlOpt; fmlOpt.name() = filePath; fmlOpt.featureSourceLayer() = filePath + "_source"; fmlOpt.enableLighting() = false; fmlOpt.styles() = new osgEarth::Symbology::StyleSheet(); fmlOpt.styles()->addStyle(style); osg::ref_ptr<osgEarth::Features::FeatureModelLayer> fml = new osgEarth::Features::FeatureModelLayer(fmlOpt); map->addLayer(fml);
2.2.1. 可见性
设置是否启用深度测试：
//可见性 osgEarth::Symbology::RenderSymbol* rs = style.getOrCreate<osgEarth::Symbology::RenderSymbol>(); rs->depthTest() = false;
2.2.2. 高度设置
//贴地设置 osgEarth::Symbology::AltitudeSymbol* alt = style.getOrCreate<osgEarth::Symbology::AltitudeSymbol>(); alt->clamping() = alt->CLAMP_TO_TERRAIN; alt->technique() = alt->TECHNIQUE_DRAPE;
osgEarth有三种设置高度的方式，分别是：贴地，相对高程和绝对高程。我这里是将其设置为贴地。
矢量贴地有多种技术实现方式，对每一种情况来说，并不存在一种最好的方式，需要根据实际的情况去设置，具体的技术说明可以参考osgEarth文档：
2.2.3. 符号化
接下来就是设置具体的样式了。这个矢量是个面矢量，所以给它设置一个面的样式，包含边界线和填充效果：
//设置矢量面样式（包括边界线） osgEarth::Symbology::LineSymbol* ls = style.getOrCreateSymbol<osgEarth::Symbology::LineSymbol>(); ls->stroke()->color() = osgEarth::Symbology::Color("#FA8072"); ls->stroke()->width() = 1.0; ls->tessellationSize()->set(100, osgEarth::Units::KILOMETERS); osgEarth::Symbology::PolygonSymbol *polygonSymbol = style.getOrCreateSymbol<osgEarth::Symbology::PolygonSymbol>(); polygonSymbol->fill()->color() = osgEarth::Symbology::Color(152.0f / 255, 251.0f / 255, 152.0f / 255, 0.8f); //238 230 133 polygonSymbol->outline() = true;
2.2.4. 显示标注
可以将矢量中存储的字段作为注记，标注在地图中。这时可以另外新建一个FeatureModelLayer图层，并且还是会用到之间已经读取好的FeatureSourceLayer，只不过显示的样式修改为文字样式TextSymbol：
void AddAnno(std::string filePath, osg::ref_ptr<osgEarth::Map> map) { osgEarth::Symbology::Style labelStyle; osgEarth::Symbology::TextSymbol* text = labelStyle.getOrCreateSymbol<osgEarth::Symbology::TextSymbol>(); string name = "[CNTRY_NAME]"; //如果需要显示汉字，则需要转换成UTF-8编码 text->content() = osgEarth::Symbology::StringExpression(name); text->priority() = osgEarth::NumericExpression( "[pop_cntry]" ); text->size() = 16.0f; text->alignment() = osgEarth::Symbology::TextSymbol::ALIGN_CENTER_CENTER; text->fill()->color() = osgEarth::Symbology::Color::White; text->halo()->color() = osgEarth::Symbology::Color::Red; text->encoding() = osgEarth::Symbology::TextSymbol::ENCODING_UTF8; //string fontFile = PathRef::GetAppDir() + "/fonts/SourceHanSansCN-Regular.ttf"; //text->font() = fontFile; //如果显示汉字，需要支持中文字库的字体 // and configure a model layer: osgEarth::Features::FeatureModelLayerOptions fmlOpt; fmlOpt.name() = filePath + "_labels"; fmlOpt.featureSourceLayer() = filePath + "_source"; fmlOpt.styles() = new osgEarth::Symbology::StyleSheet(); fmlOpt.styles()->addStyle(labelStyle); osg::ref_ptr<osgEarth::Features::FeatureModelLayer> fml = new osgEarth::Features::FeatureModelLayer(fmlOpt); map->addLayer(fml); }
注意osgEarth中显示汉字还是很麻烦的，最好矢量和代码相关的设置都是UTF-8编码的。
2.3. 其他
在最后的结果中如果线要素或者其他特征要素还是无法渲染，那么可能就是需要初始化状态设置：
//解决Lines or Annotations (FeatureNode, etc.) 不被渲染的问题 osgEarth::GLUtils::setGlobalDefaults(viewer.getCamera()->getOrCreateStateSet());
这一点在osgEarth中被提到了：
3. 结果
整理的完整代码如下：
#include <Windows.h> #include <iostream> #include <string> #include <osgViewer/Viewer> #include <osgDB/ReadFile> #include <osgEarth/MapNode> #include <osgEarth/ImageLayer> #include <osgEarth/GLUtils> #include <osgEarthDrivers/gdal/GDALOptions> #include <osgEarthDrivers/cache_filesystem/FileSystemCache> #include <osgEarthDrivers/feature_ogr/OGRFeatureOptions> #include <osgEarthFeatures/FeatureSourceLayer> #include <osgEarthFeatures/FeatureModelLayer> #include <osgEarthUtil/EarthManipulator> using namespace std; void AddAnno(std::string filePath, osg::ref_ptr<osgEarth::Map> map) { osgEarth::Symbology::Style labelStyle; osgEarth::Symbology::TextSymbol* text = labelStyle.getOrCreateSymbol<osgEarth::Symbology::TextSymbol>(); string name = "[CNTRY_NAME]"; //如果需要显示汉字，则需要转换成UTF-8编码 text->content() = osgEarth::Symbology::StringExpression(name); text->priority() = osgEarth::NumericExpression( "[pop_cntry]" ); text->size() = 16.0f; text->alignment() = osgEarth::Symbology::TextSymbol::ALIGN_CENTER_CENTER; text->fill()->color() = osgEarth::Symbology::Color::White; text->halo()->color() = osgEarth::Symbology::Color::Red; text->encoding() = osgEarth::Symbology::TextSymbol::ENCODING_UTF8; //string fontFile = PathRef::GetAppDir() + "/fonts/SourceHanSansCN-Regular.ttf"; //text->font() = fontFile; //如果显示汉字，需要支持中文字库的字体 // and configure a model layer: osgEarth::Features::FeatureModelLayerOptions fmlOpt; fmlOpt.name() = filePath + "_labels"; fmlOpt.featureSourceLayer() = filePath + "_source"; fmlOpt.styles() = new osgEarth::Symbology::StyleSheet(); fmlOpt.styles()->addStyle(labelStyle); osg::ref_ptr<osgEarth::Features::FeatureModelLayer> fml = new osgEarth::Features::FeatureModelLayer(fmlOpt); map->addLayer(fml); } void AddVector(osg::ref_ptr<osgEarth::Map> map) { // std::string filePath = "D:/Work/OSGNewBuild/osgearth-2.10.1/data/world.shp"; osgEarth::Drivers::OGRFeatureOptions featureData; featureData.url() = filePath; // 如果缺少空间参考，可以手动指定 // ifstream infile("C:/Data/vector/hs/23.prj"); // string line; // getline(infile, line); // featureData.profile()->srsString() = line; // Make a feature source layer and add it to the Map: osgEarth::Features::FeatureSourceLayerOptions ogrLayer; ogrLayer.name() = filePath + "_source"; ogrLayer.featureSource() = featureData; osgEarth::Features::FeatureSourceLayer* featureSourceLayer = new osgEarth::Features::FeatureSourceLayer(ogrLayer); map->addLayer(featureSourceLayer); osgEarth::Features::FeatureSource *features = featureSourceLayer->getFeatureSource(); if (!features) { printf(("无法打开该矢量文件！")); return; } //设置样式 osgEarth::Symbology::Style style; //可见性 osgEarth::Symbology::RenderSymbol* rs = style.getOrCreate<osgEarth::Symbology::RenderSymbol>(); rs->depthTest() = false; //贴地设置 osgEarth::Symbology::AltitudeSymbol* alt = style.getOrCreate<osgEarth::Symbology::AltitudeSymbol>(); alt->clamping() = alt->CLAMP_TO_TERRAIN; alt->technique() = alt->TECHNIQUE_DRAPE; //设置矢量面样式（包括边界线） osgEarth::Symbology::LineSymbol* ls = style.getOrCreateSymbol<osgEarth::Symbology::LineSymbol>(); ls->stroke()->color() = osgEarth::Symbology::Color("#FA8072"); ls->stroke()->width() = 1.0; ls->tessellationSize()->set(100, osgEarth::Units::KILOMETERS); osgEarth::Symbology::PolygonSymbol *polygonSymbol = style.getOrCreateSymbol<osgEarth::Symbology::PolygonSymbol>(); polygonSymbol->fill()->color() = osgEarth::Symbology::Color(152.0f / 255, 251.0f / 255, 152.0f / 255, 0.8f); //238 230 133 polygonSymbol->outline() = true; // osgEarth::Features::FeatureModelLayerOptions fmlOpt; fmlOpt.name() = filePath; fmlOpt.featureSourceLayer() = filePath + "_source"; fmlOpt.enableLighting() = false; fmlOpt.styles() = new osgEarth::Symbology::StyleSheet(); fmlOpt.styles()->addStyle(style); osg::ref_ptr<osgEarth::Features::FeatureModelLayer> fml = new osgEarth::Features::FeatureModelLayer(fmlOpt); map->addLayer(fml); AddAnno(filePath, map); } int main() { osgEarth::ProfileOptions profileOpts; //地图配置：设置缓存目录 osgEarth::Drivers::FileSystemCacheOptions cacheOpts; string cacheDir = "D:/Work/OSGNewBuild/tmp"; cacheOpts.rootPath() = cacheDir; // osgEarth::MapOptions mapOpts; mapOpts.cache() = cacheOpts; mapOpts.profile() = profileOpts; //创建地图节点 osg::ref_ptr<osgEarth::Map> map = new osgEarth::Map(mapOpts); osg::ref_ptr<osgEarth::MapNode> mapNode = new osgEarth::MapNode(map); osgEarth::Drivers::GDALOptions gdal; gdal.url() = "D:/Work/OSGNewBuild/osgearth-2.10.1/data/world.tif"; osg::ref_ptr<osgEarth::ImageLayer> layer = new osgEarth::ImageLayer("BlueMarble", gdal); map->addLayer(layer); AddVector(map); osgViewer::Viewer viewer; viewer.setSceneData(mapNode); osg::ref_ptr< osgEarth::Util::EarthManipulator> mainManipulator = new osgEarth::Util::EarthManipulator; viewer.setCameraManipulator(mainManipulator); //解决Lines or Annotations (FeatureNode, etc.) 不被渲染的问题 osgEarth::GLUtils::setGlobalDefaults(viewer.getCamera()->getOrCreateStateSet()); viewer.setUpViewInWindow(100, 100, 800, 600); return viewer.run(); }
最后的显示结果：
4. 问题
osgEarth中矢量符号化的样式机制非常强大，甚至可以将面按照线绘制，线按照点来绘制。但是这样就会造成一个问题，那就是矢量类型如果判断不正确，渲染的效果就不正确，除非事先知道是点、线或者面。可以从矢量图层中获取到FeatureSource这个类，存在的getGeometryType()接口获取的类型有时候不太正确（有时候返回成osgEarth::Symbology::Geometry::TYPE_UNKNOWN）。
一直困扰的两个问题就来了：
- 对于DXF这种可能包含点、线、面三种类型的矢量加载之后，如何设置样式，保证点按照点样式渲染，线按照线样式渲染，面按照面样式渲染呢？
- 如何修改矢量中某个或者某些特定要素的样式？最好是不重新加载数据。
这两个问题估计只能留待以后解决了。
分类: OSG
