Cog Projection

<!--
  说明：影像投影识别的中文示例，数据在页面内生成，可独立运行。
  核心逻辑：transformExtent 换算 + ImageStatic 的 projection 参数
  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>影像投影识别</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:10px;align-items:center;flex-wrap:wrap;font-size:12px;color:#58606e}
  .bar label{display:flex;gap:5px;align-items:center;cursor:pointer}
  .bar button{font:inherit;padding:3px 9px;border:1px solid #c9ced6;background:#fff;
       border-radius:5px;cursor:pointer;color:#333}
  .bar button:hover{background:#eef2f8}
  .bar input[type=range]{width:110px;vertical-align:middle}
  .bar input[type=text]{font:inherit;padding:2px 6px;border:1px solid #c9ced6;border-radius:4px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3;position:relative}
  .panel{flex:0 0 auto;max-height:34%;overflow:auto;padding:8px 12px;font-size:12px;
       background:#fff;border-top:1px solid #e3e6ea;color:#3d4451}
  .panel pre{margin:0;font-family:Consolas,"Courier New",monospace;font-size:11px;
       white-space:pre-wrap;word-break:break-all;line-height:1.5}
  .ol-attribution{font-size:11px}

</style>
</head>
<body>
<div class="bar">
<label><input type="radio" name="proj" value="3857" checked> EPSG:3857 视图</label>
<label><input type="radio" name="proj" value="4326"> EPSG:4326 视图</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') {
    var errBox = document.getElementById('map');
    if (errBox) {
      errBox.innerHTML = '<div style="padding:20px;color:#b42318">OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    }
    return;
  }

  var fromLonLat = ol.proj.fromLonLat;
  var lonlatExt = [115.9, 39.5, 116.9, 40.4];
  var ext3857 = ol.proj.transformExtent(lonlatExt, 'EPSG:4326', 'EPSG:3857');

  var W = 512;
  var canvas = document.createElement('canvas');
  canvas.width = canvas.height = W;
  var ctx = canvas.getContext('2d');
  var g = ctx.createLinearGradient(0, 0, W, W);
  g.addColorStop(0, '#1f4f7a');
  g.addColorStop(0.5, '#3d8a5f');
  g.addColorStop(1, '#c9a45b');
  ctx.fillStyle = g;
  ctx.fillRect(0, 0, W, W);
  ctx.strokeStyle = 'rgba(255,255,255,0.28)';
  for (var i = 0; i <= W; i += 64) {
    ctx.beginPath(); ctx.moveTo(i, 0); ctx.lineTo(i, W); ctx.stroke();
    ctx.beginPath(); ctx.moveTo(0, i); ctx.lineTo(W, i); ctx.stroke();
  }
  var imageUrl = canvas.toDataURL('image/png');

  var layer = new ol.layer.Image();
  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'})}), layer],
    view: new ol.View({center: fromLonLat([116.4, 39.95]), zoom: 11}),
    controls: ol.control.defaults.defaults({attribution: false, zoom: true, rotate: false})
  });

  var info = document.getElementById('info');

  function apply(code) {
    var isGeo = code === 'EPSG:4326';
    var extent = isGeo ? lonlatExt : ext3857;
    layer.setSource(new ol.source.ImageStatic({
      url: imageUrl,
      imageExtent: extent,
      projection: code
    }));

    var mid = [(lonlatExt[0] + lonlatExt[2]) / 2, (lonlatExt[1] + lonlatExt[3]) / 2];
    map.setView(new ol.View({
      projection: code,
      center: isGeo ? mid : fromLonLat(mid),
      zoom: isGeo ? 9 : 11
    }));

    info.textContent = code + ' · 范围 ' + extent.map(function (v) { return v.toFixed(2); }).join(', ');
  }

  Array.prototype.forEach.call(document.querySelectorAll('input[name=proj]'), function (r) {
    r.addEventListener('change', function () {
      apply(this.value === '4326' ? 'EPSG:4326' : 'EPSG:3857');
    });
  });

  apply('EPSG:3857');
})();
</script>
</body>
</html>