结构图解：

图元表示 Scene 中的几何图形。几何图形可以来自单个 GeometryInstance
例子1：

// Create the viewer.
const viewer = new Cesium.Viewer("cesiumContainer");
const scene = viewer.scene;// Draw a red box and position it on the globe surface.const dimensions = new Cesium.Cartesian3(400000.0, 300000.0, 500000.0);
// Box geometries are initially centered on the origin.
// We can use a model matrix to position the box on the
// globe surface.
const positionOnEllipsoid = Cesium.Cartesian3.fromDegrees(-105.0, 45.0);
const boxModelMatrix = Cesium.Matrix4.multiplyByTranslation(Cesium.Transforms.eastNorthUpToFixedFrame(positionOnEllipsoid),new Cesium.Cartesian3(0.0, 0.0, dimensions.z * 0.5),new Cesium.Matrix4()
);// 1.创建一个几何体
const boxGeometry = Cesium.BoxGeometry.fromDimensions({vertexFormat: Cesium.PerInstanceColorAppearance.VERTEX_FORMAT,dimensions: dimensions,
});
// Create a geometry instance using the geometry
// and model matrix created above.
const boxGeometryInstance = new Cesium.GeometryInstance({geometry: boxGeometry,modelMatrix: boxModelMatrix,attributes: {color: Cesium.ColorGeometryInstanceAttribute.fromColor(new Cesium.Color(1.0, 0.0, 0.0, 0.5)),},
});
// Add the geometry instance to primitives.
scene.primitives.add(new Cesium.Primitive({geometryInstances: boxGeometryInstance,//渲染样式appearance: new Cesium.PerInstanceColorAppearance({closed: true,}),})
);

例子2：创建一个圆形几何体

// Example 1: Draw a red circle on the globe surface.// Create the circle geometry.
let circleGeometry = new Cesium.CircleGeometry({center: Cesium.Cartesian3.fromDegrees(-95.0, 43.0),radius: 250000.0,vertexFormat: Cesium.PerInstanceColorAppearance.VERTEX_FORMAT,
});
// Create a geometry instance using the circle geometry
// created above. We can also specify a color attribute,
// in this case, we're creating a translucent red color.
const redCircleInstance = new Cesium.GeometryInstance({geometry: circleGeometry,attributes: {color: Cesium.ColorGeometryInstanceAttribute.fromColor(new Cesium.Color(1.0, 0.0, 0.0, 0.5)),},
});
// Add the geometry instance to primitives.
scene.primitives.add(new Cesium.Primitive({geometryInstances: redCircleInstance,appearance: new Cesium.PerInstanceColorAppearance({closed: true,}),})
);

例子3：创建一个边线几何体

// Create the viewer.
const viewer = new Cesium.Viewer("cesiumContainer");
const scene = viewer.scene;// Draw the outline of a box.const dimensions = new Cesium.Cartesian3(400000.0, 400000.0, 400000.0);// Box geometries are initially centered on the origin.
// We can use a model matrix to position the box on the
// globe surface.
const positionOnEllipsoid = Cesium.Cartesian3.fromDegrees(-106.0, 45.0);
const boxModelMatrix = Cesium.Matrix4.multiplyByTranslation(Cesium.Transforms.eastNorthUpToFixedFrame(positionOnEllipsoid),new Cesium.Cartesian3(0.0, 0.0, dimensions.z * 0.5),new Cesium.Matrix4()
);// Create a box outline geometry.
const boxOutlineGeometry = Cesium.BoxOutlineGeometry.fromDimensions({dimensions: dimensions,
});// Create a geometry instance using the geometry
// and model matrix created above.
const boxOutlineInstance = new Cesium.GeometryInstance({geometry: boxOutlineGeometry,modelMatrix: boxModelMatrix,attributes: {color: Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.WHITE),},
});// Add the geometry instance to primitives.
scene.primitives.add(new Cesium.Primitive({geometryInstances: boxOutlineInstance,appearance: new Cesium.PerInstanceColorAppearance({flat: true,renderState: {lineWidth: Math.min(2.0, scene.maximumAliasedLineWidth),},}),})
);