3D Tiles Gaussian Splats with LOD

<!--
  示例：点云的层级抽稀
  说明：五千个半透明点，按视距分四级抽稀并调整点尺寸，右上角显示当前层级
  核心逻辑：Cartesian3.distance 算视距 → 换算层级 → 按间隔显示点并改 pixelSize
  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>点云的层级抽稀</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}
  .hud{position:absolute;right:12px;top:12px;z-index:5;background:rgba(23,28,35,.9);
       border:1px solid #2a313b;border-radius:6px;padding:6px 10px;font-size:12px;color:#a2a9b6}
</style>
</head>
<body>
<div id="c"></div>
<div class="tip">滚轮缩放时右上角显示视距与层级。拉远后只显示 1/16 的点，点尺寸变大。</div>
<div id="hud" class="hud">视距 —</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 pc = scene.primitives.add(new Cesium.PointPrimitiveCollection());
  var pts = [];
  var center = Cesium.Cartesian3.fromDegrees(116.391, 39.907, 18);
  var seed = 3;
  function rnd() { seed = (seed * 9301 + 49297) % 233280; return seed / 233280; }

  for (var i = 0; i < 5000; i++) {
    var lon = 116.391 + (rnd() - 0.5) * 0.0024;
    var lat = 39.907 + (rnd() - 0.5) * 0.0018;
    var h = rnd() * 34;
    var c = Cesium.Color.fromHsl(0.55 + rnd() * 0.12, 0.55, 0.45 + rnd() * 0.3, 0.35);
    var p = pc.add({
      position: Cesium.Cartesian3.fromDegrees(lon, lat, h),
      pixelSize: 12,
      color: c
    });
    pts.push({ p: p, i: i });
  }

  var hud = document.getElementById('hud');
  var frame = 0;

  scene.postRender.addEventListener(function () {
    if (frame++ % 6 !== 0) return;          /* 每六帧更新一次，省一点计算 */
    var d = Cesium.Cartesian3.distance(viewer.camera.positionWC, center);
    var level = Math.min(4, Math.max(0, Math.floor(Math.log(d / 120) / Math.LN10 * 6)));
    var step = Math.pow(2, 4 - level) | 0;
    var size = 4 + level * 4;

    for (var k = 0; k < pts.length; k++) {
      var o = pts[k];
      o.p.show = (o.i % step) === 0;
      o.p.pixelSize = size;
    }
    hud.textContent = '视距 ' + Math.round(d) + ' 米 · 层级 L' + level + ' · 显示 ' + (1 / step * 100).toFixed(0) + '% 点';
  });

  viewer.camera.flyTo({
    destination: Cesium.Cartesian3.fromDegrees(116.391, 39.8990, 320),
    orientation: { heading: 0, pitch: Cesium.Math.toRadians(-8), roll: 0 },
    duration: 0
  });
})();
</script>
</body>
</html>