Region Growing

<!--
  示例：区域生长
  要点：以点击处为种子，按数值相近的邻域逐圈扩散，结果叠加在影像上
  依赖：OpenLayers 10.3.1 · jsDelivr CDN（底图 OSM，无 Key）
  替代：官方对多光谱影像做区域生长，这里用页面内生成的数值场做同构算法
-->
<!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>区域生长</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;color:#16181d}
  .bar{flex:0 0 auto;padding:8px 12px;background:#f6f7f9;border-bottom:1px solid #e3e6ea;
       display:flex;gap:14px;align-items:center;font-size:12px;color:#58606e;flex-wrap:wrap}
  .bar b{color:#16181d;font-weight:600}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <span>容差 <b id="tolv">0.06</b></span>
  <input type="range" id="tol" min="1" max="20" value="6" style="width:140px">
  <span>区域格数 <b id="cnt">0</b></span>
  <span>点击影像选种子点</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 (!window.ol) {
    document.getElementById('map').textContent = 'OpenLayers 加载失败，请检查 cdn.jsdelivr.net 是否可访问';
    return;
  }

  var R = 6378137;
  var DEG = 180 / Math.PI;

  var LON0 = 115.6, LON1 = 117.2, LAT0 = 39.2, LAT1 = 40.6;
  var GW = 220, GH = 180;
  var grid = new Float32Array(GW * GH);
  var mask = new Uint8Array(GW * GH);

  function valueAt(lon, lat) {
    return 0.5 + 0.32 * Math.sin(lon * 2.1) * Math.cos(lat * 1.9)
         + 0.12 * Math.sin(lon * 6.3 + 0.8) * Math.cos(lat * 5.1);
  }

  for (var gy = 0; gy < GH; gy++) {
    for (var gx = 0; gx < GW; gx++) {
      var lon = LON0 + (gx + 0.5) / GW * (LON1 - LON0);
      var lat = LAT0 + (gy + 0.5) / GH * (LAT1 - LAT0);
      grid[gy * GW + gx] = valueAt(lon, lat);
    }
  }

  var tolerance = 0.06;

  var canvasFunction = function (extent, resolution, pixelRatio, size) {
    var w = Math.max(1, Math.round(size[0]));
    var h = Math.max(1, Math.round(size[1]));
    var canvas = document.createElement('canvas');
    canvas.width = w;
    canvas.height = h;
    var ctx = canvas.getContext('2d');
    var img = ctx.createImageData(w, h);
    var sx = (extent[2] - extent[0]) / w;
    var sy = (extent[3] - extent[1]) / h;

    for (var y = 0; y < h; y++) {
      var my = extent[3] - (y + 0.5) * sy;
      var lat = (2 * Math.atan(Math.exp(my / R)) - Math.PI / 2) * DEG;
      var fy = (lat - LAT0) / (LAT1 - LAT0);
      for (var x = 0; x < w; x++) {
        var lon = (extent[0] + (x + 0.5) * sx) / R * DEG;
        var fx = (lon - LON0) / (LON1 - LON0);
        var i = (y * w + x) * 4;
        if (fx < 0 || fx >= 1 || fy < 0 || fy >= 1) {
          img.data[i + 3] = 0;
          continue;
        }
        var gxi = Math.floor(fx * GW);
        var gyi = Math.floor(fy * GH);
        var v = grid[gyi * GW + gxi];
        var isMask = mask[gyi * GW + gxi];
        img.data[i] = isMask ? 226 : 60 + v * 120;
        img.data[i + 1] = isMask ? 78 : 130 + v * 90;
        img.data[i + 2] = isMask ? 60 : 90 + v * 70;
        img.data[i + 3] = 220;
      }
    }
    ctx.putImageData(img, 0, 0);
    return canvas;
  };

  var source = new ol.source.ImageCanvas({ canvasFunction: canvasFunction });
  var layer = new ol.layer.Image({ source: source, opacity: 0.85 });

  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: ol.proj.fromLonLat([(LON0 + LON1) / 2, (LAT0 + LAT1) / 2]),
      zoom: 8
    }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  /* 4 邻域广度优先，值差不超过容差才并入 */
  function grow(startX, startY) {
    mask.fill(0);
    var seed = grid[startY * GW + startX];
    var queue = [startY * GW + startX];
    var seen = new Uint8Array(GW * GH);
    seen[startY * GW + startX] = 1;
    var total = 0;

    while (queue.length) {
      var idx = queue.pop();
      mask[idx] = 1;
      total++;
      var cx = idx % GW;
      var cy = (idx - cx) / GW;
      var nb = [[cx - 1, cy], [cx + 1, cy], [cx, cy - 1], [cx, cy + 1]];
      for (var k = 0; k < 4; k++) {
        var nx = nb[k][0], ny = nb[k][1];
        if (nx < 0 || ny < 0 || nx >= GW || ny >= GH) continue;
        var nIdx = ny * GW + nx;
        if (seen[nIdx]) continue;
        seen[nIdx] = 1;
        if (Math.abs(grid[nIdx] - seed) <= tolerance) queue.push(nIdx);
      }
    }
    document.getElementById('cnt').textContent = total;
    source.changed();
  }

  map.on('singleclick', function (evt) {
    var ll = ol.proj.toLonLat(evt.coordinate);
    var fx = (ll[0] - LON0) / (LON1 - LON0);
    var fy = (ll[1] - LAT0) / (LAT1 - LAT0);
    if (fx < 0 || fx >= 1 || fy < 0 || fy >= 1) return;
    grow(Math.floor(fx * GW), Math.floor(fy * GH));
  });

  document.getElementById('tol').addEventListener('input', function () {
    tolerance = Number(this.value) / 100;
    document.getElementById('tolv').textContent = tolerance.toFixed(2);
    mask.fill(0);
    document.getElementById('cnt').textContent = 0;
    source.changed();
  });
})();
</script>
</body>
</html>