3D Tiles Point Cloud

<!--
  示例：点云：用点勾勒城市
  说明：地面 1.5 米网格点加四栋建筑的立柱采样点，相机缓慢环绕
  核心逻辑：PointPrimitiveCollection 逐点添加 → 米到经纬度换算 → postRender 环绕相机
  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>点云：用点勾勒城市</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">地面的点稀疏发暗，建筑的点沿柱角排列。转动视角能看到体块轮廓。</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 baseLon = 116.391, baseLat = 39.906;
  var DLON = 1.17e-5, DLAT = 8.98e-6;   /* 北京纬度上 1 米对应的经纬度增量 */
  var pc = scene.primitives.add(new Cesium.PointPrimitiveCollection());
  var seed = 12;
  function rnd() { seed = (seed * 9301 + 49297) % 233280; return seed / 233280; }

  /* 地面点：30 × 20 米的网格 */
  for (var gx = -15; gx <= 15; gx += 1.5) {
    for (var gy = -10; gy <= 10; gy += 1.5) {
      var lv = 0.3 + rnd() * 0.16;
      pc.add({
        position: Cesium.Cartesian3.fromDegrees(baseLon + gx * DLON, baseLat + gy * DLAT, 0),
        pixelSize: 2,
        color: Cesium.Color.fromHsl(0.58, 0.15, lv, 0.8)
      });
    }
  }

  /* 建筑点：沿四根立柱每 2 米采一个点 */
  var blocks = [
    { dx: -8, dy: 3, w: 16, d: 12, h: 26 },
    { dx: 9, dy: 4, w: 12, d: 12, h: 38 },
    { dx: 2, dy: -6, w: 20, d: 10, h: 20 },
    { dx: -13, dy: -7, w: 10, d: 10, h: 30 }
  ];

  blocks.forEach(function (b) {
    for (var hh = 1; hh < b.h; hh += 2) {
      [-1, 1].forEach(function (sx) {
        [-1, 1].forEach(function (sy) {
          pc.add({
            position: Cesium.Cartesian3.fromDegrees(
              baseLon + (b.dx + sx * b.w / 2) * DLON,
              baseLat + (b.dy + sy * b.d / 2) * DLAT, hh),
            pixelSize: 2.4,
            color: Cesium.Color.fromHsl(0.58, 0.35, 0.28 + hh / b.h * 0.35, 0.9)
          });
        });
      });
    }
  });

  var center = Cesium.Cartesian3.fromDegrees(baseLon, baseLat, 12);
  var enu = Cesium.Transforms.eastNorthUpToFixedFrame(center);

  scene.postRender.addEventListener(function () {
    var a = performance.now() * 0.00009;
    var p = Cesium.Matrix4.multiplyByPoint(enu,
      new Cesium.Cartesian3(Math.cos(a) * 55, Math.sin(a) * 55, 26), new Cesium.Cartesian3());
    viewer.camera.setView({
      destination: p,
      orientation: { heading: a + Math.PI / 2, pitch: Cesium.Math.toRadians(-16), roll: 0 }
    });
  });
})();
</script>
</body>
</html>