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文章目录
- 综述
- 代码实现
- 代码解析
- 结果
综述
在数字孪生或者实景三维的项目中，视频融合和可视域分析，一直都是热点问题。Cesium中，支持对阴影的后处理操作，通过重新编写GLSL代码就能实现视域和视频融合的功能。ArcGIS之前支持的可视域分析只要是通过GP服务的方式去实现，并且只针对地形有相应的效果，并不能直接叠加到建模模型上。
ArcGIS for JavaScript最新发布了4.30版本的api，其中新增了对于模型场景的视域分析，并且提供了很好的交互功能，使其在项目应用中又有了更多的可能性。
代码实现
直接上代码，或者直接去官网看。
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<html lang="en"><head><meta charset="utf-8" /><meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no" /><title>Interactive viewshed analysis | Sample | ArcGIS Maps SDK for JavaScript 4.30</title><style>html,body,html,body,#viewDiv {width: 100%;height: 100%;margin: 0;padding: 0;}#viewshedComponent {width: 270px;}#viewshedComponent calcite-button {display: flex;}#promptText {margin-top: 0.4rem;}</style><link rel="stylesheet" href="https://js.arcgis.com/4.30/esri/themes/light/main.css" /><script src="https://js.arcgis.com/4.30/"></script><script type="module" src="https://js.arcgis.com/calcite-components/2.8.5/calcite.esm.js"></script><link rel="stylesheet" type="text/css" href="https://js.arcgis.com/calcite-components/2.8.5/calcite.css" /><script>require(["esri/Map","esri/views/SceneView","esri/geometry/SpatialReference","esri/core/promiseUtils","esri/core/reactiveUtils","esri/views/3d/environment/SunLighting","esri/analysis/ViewshedAnalysis","esri/analysis/Viewshed"], function (Map,SceneView,SpatialReference,promiseUtils,reactiveUtils,SunLighting,ViewshedAnalysis,Viewshed) {const view = new SceneView({container: "viewDiv",camera: {position: {spatialReference: SpatialReference.WebMercator,x: -9753837.742627423,y: 5140806.202422867,z: 995.4546383377165},heading: 1.2311944909542853,tilt: 70.07900968078631},map: new Map({basemap: "topo-3d",ground: "world-elevation"}),environment: {lighting: new SunLighting({date: new Date("January 18, 2024 12:50:00 UTC-6"),directShadowsEnabled: true})}});view.when(async () => {// Hide the 3D basemap's labels layer.const labelsLayer = view.map.basemap.referenceLayers.find((layer) => layer.title === "Places and Labels");labelsLayer.visible = false;// Create the viewshed shape.const viewshed = new Viewshed({observer: {spatialReference: SpatialReference.WebMercator,x: -9754426,y: 5143111,z: 330},farDistance: 900, // In meterstilt: 84, // Tilt of 0 looks down, tilt of 90 looks parallel to the ground, tilt of 180 looks up to the skyheading: 63, // Counted clockwise from NorthhorizontalFieldOfView: 85,verticalFieldOfView: 52});// Initialize viewshed analysis with the created viewshed shape and add it to the view.const viewshedAnalysis = new ViewshedAnalysis({ viewsheds: [viewshed] });view.analyses.add(viewshedAnalysis);// Access the viewshed's analysis view.const analysisView = await view.whenAnalysisView(viewshedAnalysis);// Make the existing analysis interactive and select the created viewshed.analysisView.interactive = true;analysisView.selectedViewshed = viewshed;// Add interactivity to the custom UI component's buttons.const createButton = document.getElementById("createButton");const cancelButton = document.getElementById("cancelButton");const promptText = document.getElementById("promptText");// Controller which allows to cancel an ongoing viewshed creation operation.let abortController = null;createButton.addEventListener("click", () => {// Cancel any pending creation operation.stopCreating();// Create a new abort controller for the new operation.abortController = new AbortController();updateUI();// Save current number of viewsheds to track whenever a new one is created.const viewshedCounter = viewshedAnalysis.viewsheds.length;// Watch whenever the a new viewshed is created and selected and then stop the creation method.reactiveUtils.when(() => viewshedAnalysis.viewsheds.length > viewshedCounter && analysisView.selectedViewshed,() => {stopCreating();updateUI();});// Pass the controller as an argument to the interactive creation method// and schedule the updateUI function after creating viewsheds is finished.analysisView.createViewsheds(abortController).catch((e) => {// When the operation is cancelled, don't do anything. Any other errors are thrown.if (!promiseUtils.isAbortError(e)) {throw e;}}).finally(() => {// Update the UI to reflect the non-creating mode.updateUI();});});cancelButton.addEventListener("click", () => {// Pressing the Cancel button stops the viewshed creation process and updates the UI accordingly.stopCreating();updateUI();});// Cancel the creation process and updates the UI when ESC is pressed.view.on("key-down", (event) => {if ((event.key = "Escape")) {stopCreating();updateUI();}});// Cancel any pending viewshed creation operation.function stopCreating() {abortController?.abort();abortController = null;}// Update the UI component according to whether there is a pending operation.function updateUI() {const creating = abortController != null;createButton.style.display = !creating ? "flex" : "none";cancelButton.style.display = creating ? "flex" : "none";promptText.style.display = creating ? "flex" : "none";}// Add the component to the UI.view.ui.add("viewshedComponent", "top-right");});});</script>
</head><body><div id="viewDiv"></div><calcite-card id="viewshedComponent"><calcite-button id="createButton">Create viewshed</calcite-button><calcite-button id="cancelButton" style="display:none">Cancel </calcite-button><div id="promptText" style="display: none"><em>Start the analysis by clicking in the scene to place the observer point and set the target.</em></div></calcite-card>
</body></html>
代码解析
ArcGIS for JavaScript提供了新的对象Viewshed和ViewshedAnalysis。
Viewshed定义了Viewshed分析的几何形状。视域由位置、距离、方向(由头部和倾斜定义)和视野角度决定。
ViewshedAnalysis允许在3D SceneView中创建和显示viewshed和view dome类型的可见性分析。该分析功能可以包含多个视图。它们可以以交互方式或编程方式创建，并且可以将分析直接添加到SceneView.analyses中。
const viewshed = new Viewshed({observer: {spatialReference: {latestWkid: 3857,wkid: 102100},x: -9754426,y: 5143111,z: 330},farDistance: 900,heading: 64,tilt: 84,horizontalFieldOfView: 85,verticalFieldOfView: 52});const viewshedAnalysis = new ViewshedAnalysis({viewsheds: [viewshed],});view.analyses.add(viewshedAnalysis);
···上面方法是直接去创建可视域的功能，当然也可以通过交互的方式去创建可视域。```javascriptconst analysisView = await view.whenAnalysisView(viewshedAnalysis);// Make the existing analysis interactive and select the created viewshed.analysisView.interactive = true;analysisView.selectedViewshed = viewshed;
analysisView.createViewsheds(abortController).catch((e) => {// When the operation is cancelled, don't do anything. Any other errors are thrown.if (!promiseUtils.isAbortError(e)) {throw e;}}).finally(() => {// Update the UI to reflect the non-creating mode.updateUI();});
结果
