Point Line Distance

<!--
  示例：点到线距离
  核心逻辑：pointToLineDistance 批量算点线距，按距离分级着色
  依赖：Turf.js 7 · 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>点到线距离</title>
<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;color:#16181d;background:#fff}
  .bar{flex:0 0 auto;display:flex;gap:12px;align-items:center;padding:8px 12px;
       background:#f6f7f9;border-bottom:1px solid #e3e6ea;font-size:12px;color:#58606e;flex-wrap:wrap}
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  .bar input[type=range]{width:150px}
  .bar b{color:#1f5fd0;font-weight:600}
  .hint{color:#8a929f}
  svg{flex:1 1 auto;min-height:0;width:100%;display:block;background:#fbfcfd}
  .out{flex:0 0 auto;display:flex;gap:20px;flex-wrap:wrap;padding:8px 12px;
       border-top:1px solid #e3e6ea;
       font-family:ui-monospace,Consolas,monospace;font-size:11.5px;color:#3a4250}
  .out b{font-weight:600;color:#1f5fd0}
</style>
</head>
<body>
<div class="bar"><span>河线固定 · 两岸 220 个观测点</span><span class="hint">颜色按距河道远近分级</span></div>
<svg id="stage" viewBox="0 0 640 320" preserveAspectRatio="xMidYMid meet"></svg>
<div class="out">
  <span>最近 <b id="min">—</b></span>
  <span>最远 <b id="max">—</b></span>
  <span>平均 <b id="avg">—</b></span>
</div>
<script src="https://cdn.jsdelivr.net/npm/@turf/turf@7/turf.min.js"></script>
<script>
(function () {
  'use strict';

  if (typeof turf === 'undefined') {
    document.body.innerHTML =
      '<div style="padding:24px;color:#b42318">Turf.js 加载失败，请检查能否访问 cdn.jsdelivr.net</div>';
    return;
  }

  function makeProjection(BOX, W, H, PAD) {
    var kx = Math.cos(((BOX[1] + BOX[3]) / 2) * Math.PI / 180);
    var x0 = BOX[0] * kx, x1 = BOX[2] * kx;
    var y0 = BOX[1], y1 = BOX[3];
    var s = Math.min((W - PAD * 2) / (x1 - x0), (H - PAD * 2) / (y1 - y0));
    var ox = (W - (x1 - x0) * s) / 2;
    var oy = (H - (y1 - y0) * s) / 2;
    var to = function (c) {
      return [(c[0] * kx - x0) * s + ox, (y1 - c[1]) * s + oy];
    };
    to.inverse = function (px, py) {
      return [((px - ox) / s + x0) / kx, y1 - (py - oy) / s];
    };
    return to;
  }

  function linePath(pr, coords) {
    var d = '';
    for (var i = 0; i < coords.length; i++) {
      var p = pr(coords[i]);
      d += (i ? 'L' : 'M') + p[0].toFixed(1) + ' ' + p[1].toFixed(1);
    }
    return d;
  }

  function ringPath(pr, ring) { return linePath(pr, ring) + 'Z'; }

  function polyPath(pr, rings) {
    var d = '';
    for (var i = 0; i < rings.length; i++) d += ringPath(pr, rings[i]);
    return d;
  }
  var BOX = [116.28, 39.82, 116.52, 39.96];
  var pr = makeProjection(BOX, 640, 320, 22);
  var stage = document.getElementById('stage');

  var river = turf.lineString([
    [116.29, 39.85], [116.34, 39.89], [116.39, 39.87],
    [116.44, 39.91], [116.49, 39.88], [116.51, 39.93]
  ]);

  var pts = [];
  for (var i = 0; i < 220; i++) {
    var p = turf.point([
      116.29 + Math.random() * 0.22,
      39.83 + Math.random() * 0.12
    ]);
    p.properties.d = turf.pointToLineDistance(p, river, { units: 'meters' });
    pts.push(p);
  }

  var dMin = Infinity, dMax = 0, sum = 0;
  pts.forEach(function (p) {
    var d = p.properties.d;
    if (d < dMin) dMin = d;
    if (d > dMax) dMax = d;
    sum += d;
  });

  function colorOf(d) {
    var t = Math.min(1, d / Math.max(dMax, 1));
    if (t < 0.25) return '#1f5fd0';
    if (t < 0.5) return '#0f8a7a';
    if (t < 0.75) return '#c08a1e';
    return '#c2410c';
  }

  var parts = ['<rect x="0" y="0" width="640" height="320" fill="none" stroke="#e3e6ea"/>'];
  parts.push('<path d="' + linePath(pr, river.geometry.coordinates) +
             '" fill="none" stroke="#6b7381" stroke-width="2.4"/>');

  pts.forEach(function (p) {
    var c = pr(p.geometry.coordinates);
    parts.push('<circle cx="' + c[0].toFixed(1) + '" cy="' + c[1].toFixed(1) +
               '" r="2.6" fill="' + colorOf(p.properties.d) + '" fill-opacity="0.8"/>');
  });

  stage.innerHTML = parts.join('');

  document.getElementById('min').textContent = dMin.toFixed(0) + ' m';
  document.getElementById('max').textContent = dMax.toFixed(0) + ' m';
  document.getElementById('avg').textContent = (sum / pts.length).toFixed(0) + ' m';
})();
</script>
</body>
</html>