osgEarth使用笔记4——加载矢量数据

目录

• 1. 概述
• 2. 详论
  • 2.1. 基本绘制
  • 2.2. 矢量符号化
    • 2.2.1. 可见性
    • 2.2.2. 高度设置
    • 2.2.3. 符号化
    • 2.2.4. 显示标注
  • 2.3. 其他
• 3. 结果
• 4. 问题

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：

1. 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？
2. 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。