JavaScript ArcGIS BaseElevationLayer用法及代码示例

AMD: require(["esri/layers/BaseElevationLayer"], (BaseElevationLayer) => { /* code goes here */ });

ESM: import BaseElevationLayer from "@arcgis/core/layers/BaseElevationLayer";

类： esri/layers/BaseElevationLayer

继承: BaseElevationLayer > Layer > Accessor

自从：用于 JavaScript 4.4 的 ArcGIS API

BaseElevationLayer 旨在扩展以创建自定义高程图层。您可以通过在 BaseElevationLayer 上调用 createSubclass() 来创建自定义 ElevationLayer。

如果新层需要获取和准备资源，您可以在加载层之前异步初始化属性。这是在 load() 方法中处理的。当图层即将显示时，此方法将由您或视图调用一次。在方法主体中，您可以调用addResolvingPromise()来添加一个承诺，该承诺必须在该层被视为已加载之前解决。

您必须覆盖 fetchTile() 方法中的逻辑才能返回自定义高程数据的值。这样做可以夸大实际高程值或将专题数据映射为高程图层。转换高程数据值时，建议保持无数据值不变。

const ExaggeratedElevationLayer = BaseElevationLayer.createSubclass({
  load: function() {
    // add loadable dependencies here and include
    // their returned promises in the
    // addResolvingPromise() method
    this._elevation = new ElevationLayer({
      url: "//elevation3d.arcgis.com/arcgis/rest/services/WorldElevation3D/Terrain3D/ImageServer"
    });
    this.addResolvingPromise(this._elevation.load());
  },

  fetchTile: function(level, row, col, options) {
    // must resolve to an object with the following properties:
    // values <number[]>: an array of elevation values for each pixel
    // width <number>: the width of the tile in pixels
    // height <number>: the height of the tile in pixels
    // noDataValue <number>: value of pixels where no elevation data is present
    return this._elevation.fetchTile(level, row, col, options).then(function(data) {
      let exaggeration = this.exaggeration;
      // `data` is an object that contains the width of the tile in pixels,
      // the height of the tile in pixels, and the values of each pixel
      for (let i = 0; i < data.values.length; i++) {
         // each value represents an elevation sample for the
         // given pixel position in the tile
         // check if the value is a no data value
         if (data.values[i] !== data.noDataValue) {
           // multiply the elevation value by the exaggeration value
           data.values[i] *= exaggeration;
         }
      }
      return data;
    }.bind(this))
  }
});

创建图层后，您必须将其添加到 Map.ground 属性的图层，并将Map添加到 SceneView 实例。

let map = new Map({
  basemap: "satellite",
  ground: {
    layers: [ new ExaggeratedElevationLayer() ]
  }
});
sceneView.map = map;