9，0级建模文件和0级精模文件写成根节点

根据以前章节所说，导出的文件是group，

此group组成

1，叶子节点

2，pagedlod

3，叶子节点和pagedLod的混合体

由于0级是由精模和简模通过pagedLod组成，所以，根节点是由0级的一个PagedLod组成，即

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osg::ref_ptr<osg::Group> grp = new osg::Group;
grp->addChild(plod);
osgDB::writeNodeFile(*grp, strOutputFileName);

输出的文件是root_0.osg

打开此文本

读取该文件

运行，

远处

拉近

代码如下：

#include <osgViewer/Viewer>

#include <osg/Node>

#include <osgdb/ReadFile>

#include <osgDB/WriteFile>

#include <osg/PagedLod>

#include <osgGA/TrackballManipulator>

int main()

{

int rootIndex = 0;

std::string strRootDir = "d:/test/lod/";

std::string strOutputFileName = strRootDir + "root_" + std::to_string(rootIndex) + ".osg";

#if 1

int childLevel = 0;

std::string strChildLevel = std::to_string(childLevel);

std::string strLevel0DetailModelFileName = strChildLevel + "/root_" + std::to_string(rootIndex) + "_detail.osg";

std::string strLevel0SimpleModelFileName = "D:/install/osg365_oe210_vs2019/OpenSceneGraph-Data/cow.osg";

osg::ref_ptrosg::PagedLOD plod = new osg::PagedLOD;

plod->setCenter(osg::Vec3(0, 0, 0));

plod->setFileName(0, strLevel0DetailModelFileName);

plod->setRange(0, 0, 50);

plod->setFileName(1, strLevel0SimpleModelFileName);

plod->setRange(1, 50, FLT_MAX);

osg::ref_ptrosg::Group grp = new osg::Group;

grp->addChild(plod);

osgDB::writeNodeFile(*grp, strOutputFileName);

#else

osg::ref_ptrosg::Node node = osgDB::readNodeFile(strOutputFileName);

osg::ref_ptrosgViewer::Viewer viewer = new osgViewer::Viewer;

viewer->setSceneData(node);

osg::ref_ptr< osgGA::TrackballManipulator> manip = new osgGA::TrackballManipulator();

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// 设置自定义的初始位置：眼睛位置、观察点、向上向量
manip->setHomePosition(
	osg::Vec3d(0.0, -100.0, 5.0),   // 眼睛位置
	osg::Vec3d(0.0, 0.0, 0.0),      // 观察中心
	osg::Vec3d(0.0, 0.0, 1.0),       // 向上向量（Z轴向上）
	false                            // 不自动计算
);

viewer->setCameraManipulator(manip);

return viewer->run();

#endif

}