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<!--
  说明：沿线参数过滤线段的中文示例，数据在页面内生成，可独立运行。
  核心逻辑：折线按累计长度分段 + 区间过滤 + 按 m 计算描边颜色
  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>沿线参数过滤线段</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>起点 m <input type="range" id="m0" min="0" max="100" value="0"></label>
<label>终点 m <input type="range" id="m1" min="0" max="100" value="30"></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 path = [
    [116.4074, 39.9042], [117.20, 36.65], [118.80, 32.06],
    [121.4737, 31.2304], [120.15, 30.27], [113.2644, 23.1291],
    [110.35, 20.02]
  ];

  /* 每段插值 24 个采样点，让 m 参数连续分布 */
  var lonlat = [];
  for (var i = 0; i < path.length - 1; i++) {
    for (var s = 0; s < 24; s++) {
      var t = s / 24;
      lonlat.push([
        path[i][0] + (path[i + 1][0] - path[i][0]) * t,
        path[i][1] + (path[i + 1][1] - path[i][1]) * t
      ]);
    }
  }
  lonlat.push(path[path.length - 1]);

  var coords = lonlat.map(function (c) { return fromLonLat(c); });
  var dist = [0];
  for (var i = 1; i < coords.length; i++) {
    var dx = coords[i][0] - coords[i - 1][0];
    var dy = coords[i][1] - coords[i - 1][1];
    dist.push(dist[i - 1] + Math.sqrt(dx * dx + dy * dy));
  }
  var total = dist[dist.length - 1];

  var segs = [];
  for (var i = 1; i < coords.length; i++) {
    segs.push({
      coords: [coords[i - 1], coords[i]],
      m0: dist[i - 1] / total,
      m1: dist[i] / total
    });
  }

  var source = new ol.source.Vector();
  var layer = new ol.layer.Vector({
    source: source,
    style: function (feature) {
      var m = feature.get('m');
      var hue = Math.round(210 - 200 * m);
      return new ol.style.Style({
        stroke: new ol.style.Stroke({color: 'hsl(' + hue + ',82%,45%)', width: 4})
      });
    }
  });

  var view = new ol.View({center: fromLonLat([115.5, 30.5]), zoom: 4.5});
  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: view,
    controls: ol.control.defaults.defaults({attribution: false, zoom: true, rotate: false})
  });

  var info = document.getElementById('info');
  var in0 = document.getElementById('m0');
  var in1 = document.getElementById('m1');

  function rebuild() {
    var a = Math.min(+in0.value, +in1.value) / 100;
    var b = Math.max(+in0.value, +in1.value) / 100;
    source.clear();
    var kept = 0;
    for (var k = 0; k < segs.length; k++) {
      var s = segs[k];
      if (s.m1 < a || s.m0 > b) { continue; }
      var f = new ol.Feature({geometry: new ol.geom.LineString(s.coords)});
      f.set('m', (s.m0 + s.m1) / 2);
      source.addFeature(f);
      kept++;
    }
    info.textContent = 'm ∈ [' + a.toFixed(2) + ', ' + b.toFixed(2) + '] · 保留 ' +
      kept + ' / ' + segs.length + ' 段 · 总长 ' + (total / 1000).toFixed(0) + ' km';
  }

  in0.addEventListener('input', rebuild);
  in1.addEventListener('input', rebuild);
  rebuild();
})();
</script>
</body>
</html>