Pmtiles Elevation

<!--
  示例：PMTiles 高程瓦片
  要点：ImageCanvas 逐像素生成高程着色图，鼠标位置反算海拔
  依赖：OpenLayers 10.3.1 · jsDelivr CDN（底图 OSM，无 Key）
  替代：官方从 PMTiles 归档读取 DEM，这里用页面内的高程函数生成等价数据
-->
<!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>PMTiles 高程瓦片</title>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/ol@10.3.1/ol.css">
<style>
  html,body{height:100%;margin:0}
  body{display:flex;flex-direction:column;overflow:hidden;
       font:13px/1.6 -apple-system,"Segoe UI","PingFang SC",sans-serif;color:#16181d}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:14px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  .bar b{color:#16181d;font-weight:600}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="checkbox" id="tglDem" checked> 高程图层</label>
  <span>海拔 <b id="h">—</b> 米</span>
  <span>鼠标移入地图读取高程</span>
</div>
<div id="map"></div>
<script src="https://cdn.jsdelivr.net/npm/ol@10.3.1/dist/ol.js"></script>
<script>
(function () {
  'use strict';
  if (!window.ol) {
    document.getElementById('map').textContent = 'OpenLayers 加载失败，请检查 cdn.jsdelivr.net 是否可访问';
    return;
  }

  var R = 6378137;
  var DEG = 180 / Math.PI;

  /* 页面内高程场：三层正弦叠加，模拟起伏地形，单位米 */
  function elevAt(lon, lat) {
    return 1500 * Math.sin(lon * 0.9) * Math.cos(lat * 1.1)
         + 700 * Math.sin(lon * 2.7 + 1.3) * Math.cos(lat * 3.1 + 0.7)
         + 180 * Math.sin(lon * 7.1 + 2.2) * Math.cos(lat * 5.3)
         + 900;
  }

  var STOPS = [
    [0.00, [42, 104, 76]],
    [0.35, [120, 166, 92]],
    [0.60, [188, 172, 110]],
    [0.80, [152, 114, 86]],
    [1.00, [246, 246, 250]]
  ];

  function colorOf(h) {
    var t = Math.max(0, Math.min(1, h / 2400));
    for (var i = 1; i < STOPS.length; i++) {
      if (t <= STOPS[i][0]) {
        var a = STOPS[i - 1], b = STOPS[i];
        var k = (t - a[0]) / (b[0] - a[0]);
        return [
          a[1][0] + (b[1][0] - a[1][0]) * k,
          a[1][1] + (b[1][1] - a[1][1]) * k,
          a[1][2] + (b[1][2] - a[1][2]) * k
        ];
      }
    }
    return STOPS[STOPS.length - 1][1];
  }

  /* 生成高程着色画布：每像素由墨卡托坐标反算经纬度 */
  var canvasFunction = function (extent, resolution, pixelRatio, size) {
    var w = Math.max(1, Math.round(size[0]));
    var h = Math.max(1, Math.round(size[1]));
    var canvas = document.createElement('canvas');
    canvas.width = w;
    canvas.height = h;
    var ctx = canvas.getContext('2d');
    var img = ctx.createImageData(w, h);
    var stepX = (extent[2] - extent[0]) / w;
    var stepY = (extent[3] - extent[1]) / h;

    for (var y = 0; y < h; y++) {
      var my = extent[3] - (y + 0.5) * stepY;
      var lat = (2 * Math.atan(Math.exp(my / R)) - Math.PI / 2) * DEG;
      for (var x = 0; x < w; x++) {
        var mx = extent[0] + (x + 0.5) * stepX;
        var lon = mx / R * DEG;
        var c = colorOf(elevAt(lon, lat));
        var i = (y * w + x) * 4;
        img.data[i] = c[0];
        img.data[i + 1] = c[1];
        img.data[i + 2] = c[2];
        img.data[i + 3] = 235;
      }
    }
    ctx.putImageData(img, 0, 0);
    return canvas;
  };

  var demLayer = new ol.layer.Image({
    opacity: 0.9,
    source: new ol.source.ImageCanvas({ canvasFunction: canvasFunction })
  });

  var map = new ol.Map({
    target: 'map',
    layers: [
      new ol.layer.Tile({ source: new ol.source.XYZ({url: 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/{z}/{y}/{x}', attributions: 'Tiles © Esri'}) }),
      demLayer
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([104.0, 30.5]),
      zoom: 6,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  document.getElementById('tglDem').addEventListener('change', function () {
    demLayer.setVisible(this.checked);
  });

  map.on('pointermove', function (evt) {
    var lonlat = ol.proj.toLonLat(evt.coordinate);
    document.getElementById('h').textContent =
      Math.round(elevAt(lonlat[0], lonlat[1]));
  });
})();
</script>
</body>
</html>