Camera Orbit

<!--
  示例：让相机绕着地标转圈
  要点：camera.lookAt 每帧按递增的航向重建位姿，配合 HeadingPitchRange 控制俯仰与距离
  依赖：CesiumJS 1.121 · jsDelivr CDN，无外部资源
-->
<!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>环绕观察</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%}
  .hud{position:absolute;left:12px;top:12px;z-index:5;background:rgba(23,28,35,.9);
       border:1px solid #2a313b;border-radius:6px;padding:9px 12px;font-size:12px;
       color:#a2a9b6;max-width:250px}
  .hud b{color:#e6e8ec;font-weight:600}
  .hud .row{margin-top:6px}
  input[type=range]{width:100%}
  .hud button{font:inherit;font-size:12px;padding:3px 9px;border-radius:4px;cursor:pointer;
       border:1px solid #343b46;background:#1d232b;color:#cfd6e2}
  .cesium-viewer-bottom .cesium-widget-credits,.cesium-viewer-animationContainer,
  .cesium-viewer-timelineContainer{display:none!important}
</style>
</head>
<body>
<div id="c"></div>
<div class="hud">
  <div><b>环绕观察</b></div>
  <div class="row">俯仰 <span id="pVal">-22</span>°</div>
  <div class="row"><input id="pitch" type="range" min="-80" max="-4" step="2" value="-22"></div>
  <div class="row">距离 <span id="rVal">1200</span> 米</div>
  <div class="row"><input id="range" type="range" min="300" max="4000" step="50" value="1200"></div>
  <div class="row"><button id="pause">暂停环绕</button></div>
</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 CENTER = Cesium.Cartesian3.fromDegrees(116.389, 39.906, 120);

  /* 中心塔 */
  viewer.entities.add({
    position: CENTER,
    cylinder: {
      length: 260, topRadius: 0, bottomRadius: 60,
      material: Cesium.Color.fromCssColorString('#4d9bff').withAlpha(0.82),
      outline: true,
      outlineColor: Cesium.Color.fromCssColorString('#cfe4ff')
    }
  });

  /* 一圈地面点，环绕时能看出方位变化 */
  var ring = [];
  for (var i = 0; i < 24; i++) {
    var a = i / 24 * Math.PI * 2;
    var lng = 116.389 + Math.cos(a) * 0.006;
    var lat = 39.906 + Math.sin(a) * 0.0045;
    ring.push(Cesium.Cartesian3.fromDegrees(lng, lat));
    viewer.entities.add({
      position: Cesium.Cartesian3.fromDegrees(lng, lat),
      point: { pixelSize: 5, color: Cesium.Color.fromCssColorString('#5f7690') }
    });
  }
  viewer.entities.add({
    polyline: {
      positions: ring.concat([ring[0]]),
      width: 1.5,
      material: new Cesium.PolylineDashMaterialProperty({
        color: Cesium.Color.fromCssColorString('#41536a'),
        dashLength: 14
      }),
      clampToGround: true
    }
  });

  var heading = 0;
  var pitch = Cesium.Math.toRadians(-22);
  var range = 1200;
  var paused = false;

  /* 每帧推进一点航向，lookAt 会重新算相机位置 */
  scene.preRender.addEventListener(function () {
    if (paused) return;
    heading += 0.0032;
    viewer.camera.lookAt(
      CENTER,
      new Cesium.HeadingPitchRange(heading, pitch, range)
    );
  });

  document.getElementById('pitch').addEventListener('input', function () {
    pitch = Cesium.Math.toRadians(parseFloat(this.value));
    document.getElementById('pVal').textContent = this.value;
  });

  document.getElementById('range').addEventListener('input', function () {
    range = parseFloat(this.value);
    document.getElementById('rVal').textContent = this.value;
  });

  document.getElementById('pause').addEventListener('click', function () {
    paused = !paused;
    this.textContent = paused ? '继续环绕' : '暂停环绕';
  });
})();
</script>
</body>
</html>