Cesium（六）添加几何图形

一、Entity API添加

var wyoming = viewer.entities.add({
      name : 'Wyoming',
      polygon : {
        hierarchy : Cesium.Cartesian3.fromDegreesArray([
                                  -109.080842,45.002073,
                                  -105.91517,45.002073,
                                  -104.058488,44.996596,
                                  -104.053011,43.002989,
                                  -104.053011,41.003906,
                                  -105.728954,40.998429,
                                  -107.919731,41.003906,
                                  -109.04798,40.998429,
                                  -111.047063,40.998429,
                                  -111.047063,42.000709,
                                  -111.047063,44.476286,
                                  -111.05254,45.002073]),
        height : 0,
        material : Cesium.Color.RED.withAlpha(0.5),
        outline : true,
        outlineColor : Cesium.Color.BLACK
      }
    });
    wyoming.polygon.height = 200000;
    wyoming.polygon.extrudedHeight = 250000;

二、Primitive API添加
Primitive由几何形状和外观两部分组成，Primitive支持的形状和外观如下图所示：
1、几何形状（Geometry）：定义了Primitive的结构，例如三角形、线条、点等。
2、外观（Appearance ）：定义Primitive的着色，包括GLSL（OpenGL着色语言，OpenGL Shading Language）顶点着色器和片段着色器，以及渲染状态。

Primitive.png

//绘制单个图形
var scene = viewer.scene;
scene.primitives.add(new Cesium.RectanglePrimitive({
    rectangle : Cesium.Rectangle.fromDegrees(-100.0, 20.0, -90.0, 30.0),//设置形状
    material : Cesium.Material.fromType('Stripe')  //设置材质
}));

//绘制多个图形
var scene = viewer.scene;
var instances = [];

for (var lon = -180.0; lon < 180.0; lon += 5.0) {
  for (var lat = -85.0; lat < 85.0; lat += 5.0) {
    instances.push(new Cesium.GeometryInstance({
      geometry : new Cesium.RectangleGeometry({
        rectangle : Cesium.Rectangle.fromDegrees(lon, lat, lon + 5.0, lat + 5.0),
        vertexFormat: Cesium.PerInstanceColorAppearance.VERTEX_FORMAT
      }),
      attributes : {
        color : Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.fromRandom({alpha : 0.5}))
      }
    }));
  }
}

scene.primitives.add(new Cesium.Primitive({
  geometryInstances : instances,
  appearance : new Cesium.PerInstanceColorAppearance()
}));

Entity和Primitive API都可以用于绘制图形，区别在于Entity是在Primitive的基础上进行了封装，用法比较简单。Primitive更接近底层，使用起来比较复杂，但效率要高于Entity。