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一、实现效果：输入中点坐标点、内圆半径、外圆半径，绘制坐标点所在高度的水平面的两个圆形形成环形区域。

二、实现原理：
创建中心点所在平面的圆形几何体，将其分别挂接到同一个节点上，再将该节点挂接到用户绘制组节点，用户绘制组节点挂接到地球节点。
三、参考代码：

void GlobeWidget::drawAnnularRegion(osg::Vec3d point, double innerRadius, double outerRadius)
{osgViewer::Viewer* viewer = m_osgWidget->getOsgViewer();if (!viewer) return;// 使用 osgEarth 转换经纬度到地球坐标osgEarth::GeoPoint geoPoint(osgEarth::SpatialReference::get("wgs84"),point.x(), point.y(), point.z(), osgEarth::ALTMODE_ABSOLUTE);osg::Vec3d cartesianCenter;geoPoint.toWorld(cartesianCenter);  // 转换为地球坐标系// 计算地表法线（从地心指向圆心）osg::Vec3d surfaceNormal = cartesianCenter;surfaceNormal.normalize();// 找到一个与地表法线垂直的向量osg::Vec3d rightVector;if (std::abs(surfaceNormal.x()) < 0.9) {rightVector = osg::Vec3d(1.0, 0.0, 0.0);} else {rightVector = osg::Vec3d(0.0, 1.0, 0.0);}rightVector = rightVector - surfaceNormal * (rightVector * surfaceNormal);rightVector.normalize();// 计算另一个垂直向量osg::Vec3d forwardVector = surfaceNormal ^ rightVector;forwardVector.normalize();// 创建环形区域的几何体osg::ref_ptr<osg::Geode> geode = new osg::Geode;osg::ref_ptr<osg::Geometry> geometry = new osg::Geometry;// 创建顶点数组osg::ref_ptr<osg::Vec3Array> vertices = new osg::Vec3Array;const int numSegments = 36;// 存储外圆顶点数量int outerVertexCount = 0;for (int i = 0; i <= numSegments; ++i) {double angle = 2.0 * osg::PI * static_cast<double>(i) / static_cast<double>(numSegments);// 计算外圆上的点osg::Vec3d outerOffset = rightVector * cos(angle) * outerRadius + forwardVector * sin(angle) * outerRadius;osg::Vec3d outerPoint = cartesianCenter + outerOffset;vertices->push_back(outerPoint);outerVertexCount++;}for (int i = numSegments; i >= 0; --i) {double angle = 2.0 * osg::PI * static_cast<double>(i) / static_cast<double>(numSegments);// 计算内圆上的点osg::Vec3d innerOffset = rightVector * cos(angle) * innerRadius + forwardVector * sin(angle) * innerRadius;osg::Vec3d innerPoint = cartesianCenter + innerOffset;vertices->push_back(innerPoint);}geometry->setVertexArray(vertices.get());// 设置颜色（透明填充，仅显示边框）osg::ref_ptr<osg::Vec4Array> colors = new osg::Vec4Array;colors->push_back(osg::Vec4(1.0f, 0.0f, 0.0f, 0.0f));geometry->setColorArray(colors.get());geometry->setColorBinding(osg::Geometry::BIND_OVERALL);// 设置外圆图元为线带geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::LINE_STRIP, 0, outerVertexCount));// 设置内圆图元为线带geometry->addPrimitiveSet(new osg::DrawArrays(osg::PrimitiveSet::LINE_STRIP, outerVertexCount, vertices->size() - outerVertexCount));// 设置虚线样式osg::ref_ptr<osg::LineStipple> lineStipple = new osg::LineStipple;lineStipple->setFactor(1);lineStipple->setPattern(0xAAAA);osg::ref_ptr<osg::StateSet> stateSet = geometry->getOrCreateStateSet();stateSet->setAttributeAndModes(lineStipple.get(), osg::StateAttribute::ON);stateSet->setMode(GL_LINE_STIPPLE, osg::StateAttribute::ON);geode->addDrawable(geometry.get());// 将 Geode 添加到根节点m_userDrawGroup->addChild(geode.get());// 强制刷新场景viewer->requestRedraw();
}```