Cesium開發高級篇 | 01空間數據可視化之Primitive - 知乎

Primitive由兩部分組成：幾何體（Geometry）和外觀（Appearance）。幾何體定義了幾何類型、位置和顏色，例如三角形、多邊形、折線、點、標簽等；外觀則定義了Primitive的著色或渲染（Shading），包括GLSL（OpenGL著色語言，OpenGL Shading Language）頂點著色器和片元著色器（ vertex and fragment shaders），以及渲染狀態（render state）。?粗略地說，幾何實例定義了結構和位置，外觀定義了視覺特征。

1.幾何類型

2.外觀

?

Cesium開發高級篇 | 02材質設置 - 知乎

Cesium中的Material類的內部機制是通過一種json格式的Fabric對象來表達物體的外觀特征，而這些外觀特征是由漫反射(diffuse)、鏡面反射(specular)、法向量(normal)、自發光(emission)以及透明度（alpha）組合（即一個Components）而成?。可通過兩種方式去獲取并設置幾何對象材質：

• Material.fromType方法
• Fabric方法

?
// Create a color material with fromType:
polygon.material = Cesium.Material.fromType('Color');
polygon.material.uniforms.color = new Cesium.Color(1.0, 1.0, 0.0, 1.0);-----------------------------------------------------------------------------
// Create the default material:
polygon.material = new Cesium.Material();
// Create a color material with full Fabric notation:
polygon.material = new Cesium.Material({fabric : {type : 'Color',uniforms : {color : new Cesium.Color(1.0, 1.0, 0.0, 1.0)}}
});?

兩種MaterialProperty

• ImageMaterialProperty 貼圖材質，可以給幾何對象表面貼上一張圖片。

var imgUrl = "./images/bumpmap.png";var imgMaterial = new Cesium.ImageMaterialProperty({image: imgUrl,repeat: new Cesium.Cartesian2(4, 4),color: Cesium.Color.BLUE,});viewer.entities.add({position: Cesium.Cartesian3.fromDegrees(-65.0, 40.0, 100000.0),ellipse: {semiMajorAxis: 300000.0, // 長半軸距離semiMinorAxis: 200000.0, // 短半軸距離height: 20000.0,material: imgMaterial,},});

• PolylineArrowMaterialProperty 帶有箭頭的線

官方案例Cesium Sandcastle

3.常見方法

getGeometryInstanceAttributes(id)

Returns the modifiable per-instance attributes for a?GeometryInstance.

返回一個GeometryInstance的可修改的每個實例屬性。

const attributes = primitive.getGeometryInstanceAttributes('an id');
attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(Cesium.Color.AQUA);
attributes.show = Cesium.ShowGeometryInstanceAttribute.toValue(true);
attributes.distanceDisplayCondition = Cesium.DistanceDisplayConditionGeometryInstanceAttribute.toValue(100.0, 10000.0);
attributes.offset = Cesium.OffsetGeometryInstanceAttribute.toValue(Cartesian3.IDENTITY);

4.貼地或貼模型特性

Cesium Sandcastle?線貼模型

Cesium Sandcastle

Cesium貼地設置_primitive貼地-CSDN博客

跟Entity[HeightReference]類似，Primitive也支持貼地或貼模型的特性，但不一樣的是，Primitive是通過classificationType屬性控制的。其中GroundPolylineGeometry、GroundPolylinePrimitive結合實現貼地線；

GroundPrimitive實現貼地幾何形狀，包括CircleGeometry、CorridorGeometry、EllipseGeometry、PolygonGeometry、RectangleGeometry；ClassificationPrimitive可實現貼地或貼模型，包括BoxGeometry、CylinderGeometry、EllipsoidGeometry、PolylineVolumeGeometry、SphereGeometry幾何形狀。

5.GroupPrimitive

GroupPrimitive表示場景中覆蓋在Terrain或3DTiles上的幾何體

• ?Support for the WEBGL_depth_texture extension is required to use GeometryInstances with different PerInstanceColors or materials besides PerInstanceColorAppearance.

(支持WEBGL_depth_texture擴展需要使用不同的PerInstanceColors或PerInstanceColor Appearance?材料的GeometryInstances。)

• Textured GroundPrimitives were designed for notional patterns and are not meant for precisely mapping textures to terrain - for that use case, use?SingleTileImageryProvider

Textured GroundPrimitives是為空想模式設計的，并不是為了精確地將紋理映射到地形。對于這種情況，使用SingleTileImageryProvider。

• For correct rendering, this feature requires the EXT_frag_depth WebGL extension. For hardware that do not support this extension, there will be rendering artifacts for some viewing angles.

為了正確渲染，這個特性需要EXT_frag_depth WebGL擴展。對于不支持此擴展的硬件，將會有一些視角的渲染工件。

• Valid geometries are?CircleGeometry,?CorridorGeometry,?EllipseGeometry,?PolygonGeometry, and?RectangleGeometry.

常見方法 ：

Cesium.GroundPrimitive.initializeTerrainHeights()?

• Initializes the minimum and maximum terrain heights. This only needs to be called if you are creating the GroundPrimitive synchronously.
• Return:A promise that will resolve once the terrain heights have been loaded.

Cesium.GroundPrimitive.isSupported(scene)

Cesium.GroundPrimitive.supportsMaterials(scene)

• Checks if the given Scene supports materials on GroundPrimitives. Materials on GroundPrimitives require support for the WEBGL_depth_texture extension.
• Return:Checks if the given Scene supports materials on GroundPrimitives. Materials on GroundPrimitives require support for the WEBGL_depth_texture extension.

getGeometryInstanceAttributes(id)

6.PrimtiveCollection

常見方法：

7.Property