Geotiff Reprojection

<!--
  示例：栅格重投影 — OpenLayers geotiff-reprojection
  核心逻辑：ImageStatic 以 EPSG:4326 声明影像范围，3857 视口下由 ol.reproj 实时重投影
  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>栅格重投影</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 label{display:flex;gap:5px;align-items:center;cursor:pointer}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label><input type="checkbox" id="tgl" checked> 经纬度影像</label>
  <label><input type="checkbox" id="frame"> 原始范围框</label>
  <span id="info">影像声明为 EPSG:4326，视口为 EPSG:3857</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;
  }

  /* 影像范围按经纬度给出：东经 100°–125°、北纬 25°–42° */
  var imageExtent = [100, 25, 125, 42];

  /* 画一张带格网与地物标记的“原始栅格” */
  function makeImage() {
    var w = 900, h = 600;
    var c = document.createElement('canvas');
    c.width = w;
    c.height = h;
    var ctx = c.getContext('2d');

    var grad = ctx.createLinearGradient(0, 0, 0, h);
    grad.addColorStop(0, '#dbe9d5');
    grad.addColorStop(0.5, '#e8dcbc');
    grad.addColorStop(1, '#c9dbe8');
    ctx.fillStyle = grad;
    ctx.fillRect(0, 0, w, h);

    /* 纹理：模拟山脊与水系 */
    ctx.strokeStyle = 'rgba(120,90,60,0.35)';
    for (var i = 0; i < 26; i++) {
      ctx.lineWidth = 1 + (i % 3);
      ctx.beginPath();
      for (var x = 0; x <= w; x += 12) {
        var y = h * (0.15 + i / 32) + 18 * Math.sin(x / 60 + i);
        x === 0 ? ctx.moveTo(x, y) : ctx.lineTo(x, y);
      }
      ctx.stroke();
    }

    ctx.strokeStyle = 'rgba(40,90,140,0.5)';
    ctx.lineWidth = 3;
    ctx.beginPath();
    ctx.moveTo(0, h * 0.72);
    ctx.bezierCurveTo(w * 0.3, h * 0.55, w * 0.6, h * 0.9, w, h * 0.6);
    ctx.stroke();

    /* 经纬网，间距 5° */
    ctx.strokeStyle = 'rgba(0,0,0,0.22)';
    ctx.lineWidth = 1;
    ctx.font = '12px sans-serif';
    ctx.fillStyle = 'rgba(0,0,0,0.55)';
    for (var lon = 100; lon <= 125; lon += 5) {
      var px = (lon - 100) / 25 * w;
      ctx.beginPath();
      ctx.moveTo(px, 0);
      ctx.lineTo(px, h);
      ctx.stroke();
      ctx.fillText(lon + '°E', px + 4, 16);
    }
    for (var lat = 25; lat <= 42; lat += 5) {
      var py = (42 - lat) / 17 * h;
      ctx.beginPath();
      ctx.moveTo(0, py);
      ctx.lineTo(w, py);
      ctx.stroke();
      ctx.fillText(lat + '°N', 4, py - 4);
    }

    return c.toDataURL();
  }

  var imageSource = new ol.source.ImageStatic({
    url: makeImage(),
    /* 关键：影像自带投影信息，交给渲染层重投影 */
    projection: 'EPSG:4326',
    imageExtent: imageExtent,
    crossOrigin: 'anonymous'
  });

  var imageLayer = new ol.layer.Image({ source: imageSource });

  /* 原始范围框：经纬度矩形的四条边，同样要转到 3857 */
  var frameSource = new ol.source.Vector({
    features: [new ol.Feature({
      geometry: new ol.geom.Polygon([[
        [imageExtent[0], imageExtent[1]],
        [imageExtent[2], imageExtent[1]],
        [imageExtent[2], imageExtent[3]],
        [imageExtent[0], imageExtent[3]],
        [imageExtent[0], imageExtent[1]]
      ]]).transform('EPSG:4326', 'EPSG:3857')
    })]
  });

  var frameLayer = new ol.layer.Vector({
    source: frameSource,
    visible: false,
    style: new ol.style.Style({
      stroke: new ol.style.Stroke({ color: '#c92a2a', width: 2, lineDash: [6, 4] })
    })
  });

  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'}) }),
      imageLayer,
      frameLayer
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([112.5, 33.5]),
      zoom: 5,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  document.getElementById('tgl').addEventListener('change', function () {
    imageLayer.setVisible(this.checked);
  });
  document.getElementById('frame').addEventListener('change', function () {
    frameLayer.setVisible(this.checked);
  });
})();
</script>
</body>
</html>