Measure

<!--
  示例：测量距离
  要点：绘制折线时用 ol.sphere.getLength 实时算球面长度，Overlay 跟随鼠标
  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>测量距离</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 button{font:inherit;font-size:12px;padding:4px 9px;border:1px solid #ccd1d9;
       border-radius:4px;background:#fff;color:#16181d;cursor:pointer}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
  .tipbox{background:#16181d;color:#fff;padding:3px 8px;border-radius:4px;
       font-size:12px;white-space:nowrap}
  .tipbox::after{content:"";position:absolute;left:50%;bottom:-5px;margin-left:-5px;
       border:5px solid transparent;border-top-color:#16181d;border-bottom:0}
</style>
</head>
<body>
<div class="bar">
  <span>单击落点，双击结束测量</span>
  <button id="clear">清空</button>
  <span id="total">总长度：—</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 fromLonLat = ol.proj.fromLonLat;

  var measureSource = new ol.source.Vector();

  var measureLayer = new ol.layer.Vector({
    source: measureSource,
    style: new ol.style.Style({
      stroke: new ol.style.Stroke({ color: '#d0453a', width: 3 }),
      fill: new ol.style.Fill({ color: 'rgba(208,69,58,0.12)' })
    })
  });

  var tipEl = document.createElement('div');
  tipEl.className = 'tipbox';
  tipEl.textContent = '';

  var tipOverlay = new ol.Overlay({
    element: tipEl,
    positioning: 'bottom-center',
    offset: [0, -12],
    stopEvent: false
  });

  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'}) }),
      measureLayer
    ],
    overlays: [tipOverlay],
    view: new ol.View({
      center: fromLonLat([116.400, 39.915]),
      zoom: 12
    })
  });

  var totalEl = document.getElementById('total');

  function formatLength(line) {
    var meters = ol.sphere.getLength(line);
    return meters >= 1000
      ? (meters / 1000).toFixed(2) + ' 公里'
      : meters.toFixed(0) + ' 米';
  }

  var draw = new ol.interaction.Draw({
    source: measureSource,
    type: 'LineString',
    style: new ol.style.Style({
      stroke: new ol.style.Stroke({ color: '#d0453a', width: 3, lineDash: [8, 5] })
    })
  });

  map.addInteraction(draw);

  /* 绘制过程中跟随鼠标显示累计长度 */
  draw.on('drawstart', function (evt) {
    var geom = evt.feature.getGeometry();

    var moveListener = function (e) {
      if (e.dragging) return;
      var clone = geom.clone();
      clone.appendCoordinate(e.coordinate);
      tipEl.textContent = formatLength(clone);
      tipOverlay.setPosition(e.coordinate);
    };

    map.on('pointermove', moveListener);

    draw.once('drawend', function () {
      map.un('pointermove', moveListener);
      tipOverlay.setPosition(undefined);
    });

    draw.once('drawabort', function () {
      map.un('pointermove', moveListener);
      tipOverlay.setPosition(undefined);
    });
  });

  draw.on('drawend', function (evt) {
    totalEl.textContent = '总长度：' + formatLength(evt.feature.getGeometry());
  });

  document.getElementById('clear').addEventListener('click', function () {
    measureSource.clear();
    totalEl.textContent = '总长度：—';
  });
})();
</script>
</body>
</html>