Sentinel Hub Date Picker

<!--
  示例：按日期取影像
  要点：日期控件改变成像季节参数，ImageCanvas 随即重绘
  依赖：OpenLayers 10.3.1 · jsDelivr CDN（底图 OSM，无 Key）
  替代：官方按日期向 Sentinel Hub 请求影像，这里用日期换算季节因子生成影像
-->
<!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>按日期取影像</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 input{font-size:12px;padding:2px 4px}
  .bar b{color:#16181d;font-weight:600}
  #map{flex:1 1 auto;min-height:0;background:#eef0f3}
</style>
</head>
<body>
<div class="bar">
  <label>成像日期 <input type="date" id="d" value="2026-04-15" min="2026-01-01" max="2026-12-31"></label>
  <span>季节相位 <b id="ph">—</b></span>
  <span>云量 <b id="cl">—</b></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 phase = 0.25;

  function dayOfYear(str) {
    var d = new Date(str + 'T00:00:00');
    if (isNaN(d.getTime())) return 105;
    var start = new Date(d.getFullYear(), 0, 0);
    return Math.floor((d - start) / 86400000);
  }

  function renderPixel(lon, lat) {
    /* 植被随季节相位在绿与褐之间摆动 */
    var green = 0.5 + 0.32 * Math.sin(phase * Math.PI * 2);
    var r = 0.30 + 0.12 * Math.sin(lon * 2.2) + (1 - green) * 0.12;
    var g = 0.22 + green * 0.34 + 0.08 * Math.cos(lat * 2.4);
    var b = 0.22 + 0.10 * Math.cos(lon * 3.1 + lat);
    return [
      Math.round(Math.min(255, r * 255)),
      Math.round(Math.min(255, g * 255)),
      Math.round(Math.min(255, b * 255))
    ];
  }

  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;
      for (var x = 0; x < w; x++) {
        var lon = (extent[0] + (x + 0.5) * sx) / R * DEG;
        var c = renderPixel(lon, lat);
        var i = (y * w + x) * 4;
        img.data[i] = c[0];
        img.data[i + 1] = c[1];
        img.data[i + 2] = c[2];
        img.data[i + 3] = 255;
      }
    }
    ctx.putImageData(img, 0, 0);
    return canvas;
  };

  var source = new ol.source.ImageCanvas({ canvasFunction: canvasFunction });

  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'}) }),
      new ol.layer.Image({ source: source, opacity: 0.8 })
    ],
    view: new ol.View({ center: ol.proj.fromLonLat([113.5, 34.5]), zoom: 7 }),
    controls: ol.control.defaults.defaults({ attribution: false, rotate: false })
  });

  function update() {
    var doy = dayOfYear(document.getElementById('d').value);
    phase = (doy - 80) / 365;
    document.getElementById('ph').textContent = phase.toFixed(2);
    /* 云量随相位取个稳定值，仅作信息展示 */
    var cloud = 18 + Math.round(Math.abs(Math.sin(phase * Math.PI * 3)) * 46);
    document.getElementById('cl').textContent = cloud + '%';
    source.changed();
  }

  document.getElementById('d').addEventListener('change', update);
  update();
})();
</script>
</body>
</html>