Geozarr Datacube

<!--
  示例：GeoZarr 数据立方 — OpenLayers geozarr-datacube
  核心逻辑：同一块多波段数据按选择器切换波段，Raster 源用不同色带渲染单波段结果
  依赖：OpenLayers 10.3.1 · 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>GeoZarr 数据立方</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}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:12px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar select{font:inherit;padding:3px 6px;border:1px solid #ccd2da;border-radius:3px;background:#fff}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label>波段
    <select id="band">
      <option value="0">B04 红光</option>
      <option value="1">B08 近红外</option>
      <option value="2">B11 短波红外</option>
      <option value="idx">NDVI 指数</option>
    </select>
  </label>
  <span id="info">—</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 (typeof ol === 'undefined') {
    document.getElementById('map').innerHTML =
      '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  /* 一次生成三波段数据，后续切换只是换读取通道 */
  function makeCube() {
    var size = 512;
    var c = document.createElement('canvas');
    c.width = size;
    c.height = size;
    var ctx = c.getContext('2d');
    var img = ctx.createImageData(size, size);

    for (var y = 0; y < size; y++) {
      for (var x = 0; x < size; x++) {
        var veg = 0.5 + 0.36 * Math.sin(x / 51) * Math.cos(y / 38) +
          0.14 * Math.sin((x - y) / 23);
        veg = Math.max(0, Math.min(1, veg));
        var i = (y * size + x) * 4;
        img.data[i] = Math.round(50 + 70 * (1 - veg));
        img.data[i + 1] = Math.round(70 + 160 * veg);
        img.data[i + 2] = Math.round(55 + 90 * (1 - veg) + 20 * Math.sin(y / 13));
        img.data[i + 3] = 255;
      }
    }
    ctx.putImageData(img, 0, 0);
    return { url: c.toDataURL(), data: img.data };
  }

  var cubeData = makeCube();

  /* 每个通道的均值在渲染前算好，供状态栏显示 */
  function channelMean(key) {
    var data = cubeData.data;
    var sum = 0, count = 0;
    for (var i = 0; i < data.length; i += 4) {
      var v;
      if (key === 'idx') {
        v = (data[i + 1] - data[i]) / Math.max(1, data[i + 1] + data[i]);
        v = Math.max(0, Math.min(1, (v + 0.2) / 1.2));
      } else {
        v = data[i + Number(key)] / 255;
      }
      sum += v;
      count++;
    }
    return sum / count;
  }

  var extent = ol.proj.transformExtent(
    [116.15, 39.78, 116.60, 40.06], 'EPSG:4326', 'EPSG:3857'
  );

  var cube = new ol.source.ImageStatic({
    url: cubeData.url,
    projection: 'EPSG:3857',
    imageExtent: extent,
    crossOrigin: 'anonymous'
  });

  var PALETTES = {
    '0': [[0, 40, 40, 40], [1, 235, 220, 200]],
    '1': [[0, 25, 45, 30], [1, 210, 245, 190]],
    '2': [[0, 30, 35, 55], [1, 215, 205, 185]],
    'idx': [[0, 150, 120, 70], [0.5, 220, 215, 120], [1, 30, 90, 45]]
  };

  function paletteFor(key, t) {
    var stops = PALETTES[key];
    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 [
          Math.round(a[1] + (b[1] - a[1]) * k),
          Math.round(a[2] + (b[2] - a[2]) * k),
          Math.round(a[3] + (b[3] - a[3]) * k)
        ];
      }
    }
    var last = stops[stops.length - 1];
    return [last[1], last[2], last[3]];
  }

  var layer = new ol.layer.Image({ opacity: 0.85 });
  var current = '0';

  function rebuild() {
    var key = current;
    var band = key === 'idx' ? -1 : Number(key);

    layer.setSource(new ol.source.Raster({
      sources: [cube],
      operation: function (pixels) {
        var src = pixels[0];
        var out = new Uint8ClampedArray(src.length);

        for (var i = 0; i < src.length; i += 4) {
          var value;
          if (band >= 0) {
            value = src[i + band] / 255;
          } else {
            var red = src[i], nir = src[i + 1];
            value = (nir - red) / Math.max(1, nir + red);
            value = Math.max(0, Math.min(1, (value + 0.2) / 1.2));
          }
          var rgb = paletteFor(key, value);
          out[i] = rgb[0];
          out[i + 1] = rgb[1];
          out[i + 2] = rgb[2];
          out[i + 3] = 255;
        }
        return out;
      }
    }));
  }

  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'}), opacity: 0.5 }),
      layer
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.38, 39.92]),
      zoom: 11,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  layer.on('change', function () {
    var mean = channelMean(current);
    document.getElementById('info').textContent =
      '均值 ' + mean.toFixed(3) + ' · 通道 ' + current;
  });

  document.getElementById('band').addEventListener('change', function () {
    current = this.value;
    rebuild();
    var mean = channelMean(current);
    document.getElementById('info').textContent =
      '均值 ' + mean.toFixed(3) + ' · 通道 ' + current;
  });

  rebuild();
})();
</script>
</body>
</html>