Resolution Zoom

<!--
  示例：分辨率与缩放
  要点：getResolution / getResolutionForZoom / getZoomForResolution 三者对照
  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>分辨率与缩放</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:8px;align-items:center;font-size:12px;color:#58606e}
  .bar button{padding:3px 9px;border:1px solid #cfd4dc;border-radius:4px;
              background:#fff;cursor:pointer;font-size:12px}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <button data-z="5">z5</button>
  <button data-z="8">z8</button>
  <button data-z="11">z11</button>
  <button data-z="14">z14</button>
  <button data-z="17">z17</button>
  <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;
  }

  var view = new ol.View({
    center: ol.proj.fromLonLat([116.3974, 39.9093]),
    zoom: 11
  });

  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'}) })],
    view: view,
    controls: ol.control.defaults.defaults({ attribution: false })
  });

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

  function report() {
    var res = view.getResolution();
    /* 当前分辨率反算层级 */
    var zFromRes = view.getZoomForResolution(res);
    /* 层级正算分辨率，四舍五入到整数层级作对照 */
    var resAt = view.getResolutionForZoom(Math.round(view.getZoom()));

    info.textContent =
      '分辨率 ' + res.toFixed(2) + ' m/px' +
      ' · 反算层级 ' + zFromRes.toFixed(2) +
      ' · 整级分辨率 ' + resAt.toFixed(2);
  }

  view.on('change:resolution', report);
  report();

  Array.prototype.forEach.call(document.querySelectorAll('[data-z]'), function (btn) {
    btn.addEventListener('click', function () {
      view.animate({ zoom: Number(btn.dataset.z), duration: 350 });
    });
  });
})();
</script>
</body>
</html>