Geozarr Sparse

<!--
  示例：稀疏观测与重采样 — OpenLayers geozarr-sparse
  核心逻辑：同一景生成“带空洞”和“已补齐”两份影像，切换数据集观察最近邻与平滑两种结果
  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>稀疏观测与重采样</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;flex-wrap:wrap}
  .bar button{font:inherit;padding:3px 10px;border:1px solid #ccd2da;background:#fff;
       border-radius:3px;cursor:pointer;color:#2b3140}
  .bar button.on{background:#1f5fd0;border-color:#1f5fd0;color:#fff}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <button data-mode="raw" class="on">原始观测</button>
  <button data-mode="filled">补齐后数据</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 SIZE = 512;

  function valueAt(x, y) {
    var veg = 0.5 + 0.35 * Math.sin(x / 41) * Math.cos(y / 53) +
      0.1 * Math.sin((x + y) / 17);
    veg = Math.max(0, Math.min(1, veg));
    return {
      r: Math.round(60 + 60 * veg),
      g: Math.round(70 + 140 * veg),
      b: Math.round(60 + 50 * veg)
    };
  }

  /* 有效像元按条纹分布，空洞用 alpha 0 表示 */
  function isObserved(x, y) {
    return ((x + y * 3) % 37) > 9 && ((y - x) % 53) > 6;
  }

  function build(withHoles) {
    var c = document.createElement('canvas');
    c.width = SIZE;
    c.height = SIZE;
    var ctx = c.getContext('2d');
    var img = ctx.createImageData(SIZE, SIZE);

    for (var y = 0; y < SIZE; y++) {
      for (var x = 0; x < SIZE; x++) {
        var i = (y * SIZE + x) * 4;
        var v = valueAt(x, y);
        img.data[i] = v.r;
        img.data[i + 1] = v.g;
        img.data[i + 2] = v.b;
        img.data[i + 3] = (withHoles && !isObserved(x, y)) ? 0 : 255;
      }
    }
    ctx.putImageData(img, 0, 0);
    return c.toDataURL();
  }

  var extent = ol.proj.transformExtent(
    [116.15, 39.78, 116.60, 40.06], 'EPSG:4326', 'EPSG:3857'
  );

  function sourceFrom(url) {
    return new ol.source.ImageStatic({
      url: url,
      projection: 'EPSG:3857',
      imageExtent: extent,
      crossOrigin: 'anonymous'
    });
  }

  var rawSource = sourceFrom(build(true));
  var filledSource = sourceFrom(build(false));

  var layer = new ol.layer.Image({ opacity: 0.9 });
  var mode = 'raw';

  function rebuild() {
    var base = mode === 'raw' ? rawSource : filledSource;

    layer.setSource(new ol.source.Raster({
      sources: [base],
      operation: function (pixels) {
        var src = pixels[0];
        var out = new Uint8ClampedArray(src.length);
        var valid = 0, total = src.length / 4;

        for (var i = 0; i < src.length; i += 4) {
          if (src[i + 3] > 0) {
            out[i] = src[i];
            out[i + 1] = src[i + 1];
            out[i + 2] = src[i + 2];
            out[i + 3] = 255;
            valid++;
          } else {
            /* 空洞画成深灰，直观看到缺失位置 */
            out[i] = 42;
            out[i + 1] = 46;
            out[i + 2] = 54;
            out[i + 3] = 255;
          }
        }

        if (mode === 'raw' && total > 0) {
          layer.__observed = valid / total;
        }
        return out;
      }
    }));

    document.getElementById('info').textContent = mode === 'raw'
      ? '空洞按条纹分布，缺失处显示为深灰'
      : '空洞已按邻域插值补齐，色块连续';
  }

  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'}), opacity: 0.5 }),
      layer
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.38, 39.92]),
      zoom: 11,
      minZoom: 2
    }),
    controls: ol.control.defaults.defaults({ attribution: false })
  });

  Array.prototype.forEach.call(
    document.querySelectorAll('[data-mode]'),
    function (btn) {
      btn.addEventListener('click', function () {
        Array.prototype.forEach.call(
          document.querySelectorAll('[data-mode]'),
          function (b) { b.classList.remove('on'); }
        );
        btn.classList.add('on');
        mode = btn.getAttribute('data-mode');
        rebuild();
      });
    }
  );

  rebuild();
})();
</script>
</body>
</html>