Geometry Height Reference

<!--
  示例：高度参考
  说明：三个盒体分别用绝对高度、贴地与相对高度，观察它们与地表的贴合关系
  核心逻辑：heightReference = NONE / CLAMP_TO_GROUND / RELATIVE_TO_GROUND
  依赖：CesiumJS 1.121 · jsDelivr CDN
-->
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta name="robots" content="noindex,follow">
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>高度参考</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/cesium@1.121.0/Build/Cesium/Widgets/widgets.css">
<style>
  html,body{height:100%;margin:0}
  body{background:#0e1116;color:#e6e8ec;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif}
  #c{height:100%}
  .tip{position:absolute;left:12px;top:12px;z-index:5;
       background:rgba(23,28,35,.9);border:1px solid #2a313b;border-radius:6px;
       padding:8px 12px;font-size:12px;color:#a2a9b6;max-width:320px;line-height:1.6}

  .cesium-viewer-bottom .cesium-widget-credits,.cesium-viewer-animationContainer,
  .cesium-viewer-timelineContainer{display:none!important}
</style>
</head>
<body>
<div id="c"></div>
<div class="tip">贴地盒体紧贴球面，相对高度盒体从地表往上长，绝对高度会浮在空中。</div>
<script src="https://cdn.jsdelivr.net/npm/cesium@1.121.0/Build/Cesium/Cesium.js"></script>
<script>
(function () {
  'use strict';

  var viewer = new Cesium.Viewer('c', {
    baseLayer: false,
    baseLayerPicker: false, geocoder: false, homeButton: false,
    sceneModePicker: false, navigationHelpButton: false,
    animation: false, timeline: false, fullscreenButton: false,
    infoBox: false, selectionIndicator: false
  });

  var scene = viewer.scene;
  scene.globe.baseColor = Cesium.Color.fromCssColorString('#1c2733');
  scene.backgroundColor = Cesium.Color.fromCssColorString('#0e1116');
  scene.skyBox.show = false;
  scene.sun.show = false;
  scene.moon.show = false;
  if (scene.skyAtmosphere) scene.skyAtmosphere.show = false;

  var lon = 116.3855, lat = 39.9030;

  function addBox(dx, ref, height, color, labelZ) {
    viewer.entities.add({
      position: Cesium.Cartesian3.fromDegrees(lon + dx, lat, labelZ),
      box: {
        dimensions: new Cesium.Cartesian3(26, 26, 26),
        heightReference: ref,
        material: Cesium.Color.fromCssColorString(color).withAlpha(0.9),
        outline: true,
        outlineColor: Cesium.Color.fromCssColorString('#0e1116')
      }
    });
  }

  addBox(0.0000, Cesium.HeightReference.NONE, 0, '#4d86c8', 120);
  addBox(0.0034, Cesium.HeightReference.CLAMP_TO_GROUND, 0, '#5bb08a', 120);
  addBox(0.0068, Cesium.HeightReference.RELATIVE_TO_GROUND, 40, '#d08a4e', 120);
  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.3900, 39.8996, 480),
    orientation: { heading: Cesium.Math.toRadians(0), pitch: Cesium.Math.toRadians(-28), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>