Raster

<!--
  示例：栅格影像运算
  要点：ImageCanvas 里逐像素合成两个波段，切换运算式即时重绘
  依赖：OpenLayers 10.3.1 · jsDelivr CDN（底图 OSM，无 Key）
  替代：官方用 ol.source.Raster 组合两幅 GeoTIFF，这里用页面内生成的双波段数据
-->
<!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>栅格影像运算</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 b{color:#16181d;font-weight:600}
  .bar select{font-size:12px;padding:2px 4px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label>运算
    <select id="op">
      <option value="nd">归一化差值 (A-B)/(A+B)</option>
      <option value="sum">波段相加</option>
      <option value="gray">灰度 A</option>
      <option value="invert">反色</option>
    </select>
  </label>
  <span>不透明度 <b id="ov">70</b>%</span>
  <input type="range" id="op2" min="0" max="100" value="70" style="width:120px">
</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;
  var mode = 'nd';

  /* 两个合成波段：低频起伏 + 细节，范围 0..1 */
  function bandA(lon, lat) {
    return 0.5 + 0.35 * Math.sin(lon * 1.4) * Math.cos(lat * 1.1)
         + 0.1 * Math.sin(lon * 5.3 + 1.1);
  }
  function bandB(lon, lat) {
    return 0.5 + 0.3 * Math.cos(lon * 1.1 + 0.4) * Math.sin(lat * 1.6)
         + 0.1 * Math.cos(lat * 4.7);
  }

  function combine(a, b) {
    if (mode === 'sum') {
      var s = Math.min(1, (a + b) / 2);
      return [s * 230, s * 200, 90 + s * 120];
    }
    if (mode === 'gray') {
      var g = a * 255;
      return [g, g, g];
    }
    if (mode === 'invert') {
      return [255 - a * 235, 255 - b * 235, 255 - (a + b) * 120];
    }
    var d = (a - b) / (a + b + 0.0001);
    if (d >= 0) return [60 + d * 150, 150 + d * 60, 80];
    return [120, 120 + (-d) * 90, 120 + (-d) * 110];
  }

  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 sx = (extent[2] - extent[0]) / w;
    var sy = (extent[3] - extent[1]) / h;

    for (var y = 0; y < h; y++) {
      var my = extent[3] - (y + 0.5) * sy;
      var lat = (2 * Math.atan(Math.exp(my / R)) - Math.PI / 2) * DEG;
      for (var x = 0; x < w; x++) {
        var lon = (extent[0] + (x + 0.5) * sx) / R * DEG;
        var c = combine(bandA(lon, lat), bandB(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] = 255;
      }
    }
    ctx.putImageData(img, 0, 0);
    return canvas;
  };

  var source = new ol.source.ImageCanvas({ canvasFunction: canvasFunction });
  var rasterLayer = new ol.layer.Image({ source: source, opacity: 0.7 });

  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'}) }), rasterLayer],
    view: new ol.View({ center: ol.proj.fromLonLat([104.0, 30.5]), zoom: 5 }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  document.getElementById('op').addEventListener('change', function () {
    mode = this.value;
    source.changed();
  });

  document.getElementById('op2').addEventListener('input', function () {
    document.getElementById('ov').textContent = this.value;
    rasterLayer.setOpacity(this.value / 100);
  });
})();
</script>
</body>
</html>