WMTS Layer From Capabilities

<!--
  示例：OpenLayers 从能力文档建 WMTS
  要点：optionsFromCapabilities 把能力文档转成 WMTS 构造参数，直接创建图层
  依赖：OpenLayers 10.3.1 · jsDelivr CDN
-->
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  <span id="info">解析能力文档…</span>
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<script>
(function () {
  'use strict';

  if (typeof ol === 'undefined') {
    document.getElementById('map').textContent = 'OpenLayers 加载失败，请检查能否访问 cdn.jsdelivr.net';
    return;
  }

  /* ---- 页面内合成的区县面，代替外部 WMS 服务返回的影像 ---- */
  var SYNTH_REGIONS = [
    {name: '海淀', color: '#a9c9ec', pts: [[116.14, 39.94], [116.34, 39.94], [116.34, 40.06], [116.14, 40.06]]},
    {name: '朝阳', color: '#b7dbb2', pts: [[116.44, 39.90], [116.62, 39.90], [116.62, 40.05], [116.44, 40.05]]},
    {name: '西城', color: '#efcf9f', pts: [[116.32, 39.88], [116.40, 39.88], [116.40, 39.96], [116.32, 39.96]]},
    {name: '东城', color: '#e8aabf', pts: [[116.40, 39.88], [116.48, 39.88], [116.48, 39.96], [116.40, 39.96]]},
    {name: '丰台', color: '#bdafd9', pts: [[116.18, 39.78], [116.40, 39.78], [116.40, 39.88], [116.18, 39.88]]},
    {name: '大兴', color: '#9ed0c9', pts: [[116.28, 39.62], [116.56, 39.62], [116.56, 39.78], [116.28, 39.78]]}
  ];

  var SYNTH_RIVER = [[116.10, 40.00], [116.22, 39.95], [116.34, 39.94], [116.45, 39.90], [116.58, 39.86]];

  function synthParam(src, name) {
    var m = new RegExp('[?&]' + name + '=([^&]*)').exec(src || '');
    return m ? decodeURIComponent(m[1].replace(/\+/g, ' ')) : '';
  }

  function synthDraw(ctx, w, h, bbox, opt) {
    opt = opt || {};
    var x0 = bbox[0], y0 = bbox[1], x1 = bbox[2], y1 = bbox[3];
    if (!isFinite(x0) || !(x1 > x0) || !(y1 > y0)) {
      return;
    }
    var project = opt.project || ol.proj.fromLonLat;
    function px(c) {
      return [(c[0] - x0) / (x1 - x0) * w, (y1 - c[1]) / (y1 - y0) * h];
    }
    ctx.fillStyle = opt.background || '#eef2f6';
    ctx.fillRect(0, 0, w, h);

    /* 河流 */
    var river = SYNTH_RIVER.map(function (p) { return px(project(p)); });
    ctx.beginPath();
    ctx.moveTo(river[0][0], river[0][1]);
    for (var r = 1; r < river.length; ++r) {
      ctx.lineTo(river[r][0], river[r][1]);
    }
    ctx.strokeStyle = '#7fb6d9';
    ctx.lineWidth = Math.max(2, w / 60);
    ctx.stroke();

    /* 区县面 */
    var palette = opt.palette;
    SYNTH_REGIONS.forEach(function (region, i) {
      var pts = region.pts.map(function (p) { return px(project(p)); });
      ctx.beginPath();
      ctx.moveTo(pts[0][0], pts[0][1]);
      for (var j = 1; j < pts.length; ++j) {
        ctx.lineTo(pts[j][0], pts[j][1]);
      }
      ctx.closePath();
      ctx.globalAlpha = 0.88;
      ctx.fillStyle = palette ? palette[i % palette.length] : region.color;
      ctx.fill();
      ctx.globalAlpha = 1;
      ctx.strokeStyle = '#5c6b7a';
      ctx.lineWidth = 1;
      ctx.stroke();

      if (w >= 200) {
        var cx = 0, cy = 0;
        pts.forEach(function (p) { cx += p[0]; cy += p[1]; });
        cx /= pts.length;
        cy /= pts.length;
        ctx.fillStyle = '#24313d';
        ctx.font = '500 ' + Math.max(9, Math.round(w / 22)) + 'px sans-serif';
        ctx.textAlign = 'center';
        ctx.textBaseline = 'middle';
        ctx.fillText(region.name, cx, cy);
      }
    });

    /* 时间动画用的降水色块 */
    if (opt.time) {
      var seed = 0;
      for (var k = 0; k < opt.time.length; ++k) {
        seed = (seed * 31 + opt.time.charCodeAt(k)) % 9973;
      }
      ctx.globalAlpha = 0.35;
      for (var n = 0; n < 5; ++n) {
        var fx = ((seed + n * 137) % 100) / 100;
        var fy = ((seed + n * 71) % 100) / 100;
        ctx.beginPath();
        ctx.ellipse(fx * w, fy * h, w / 12, h / 18, 0, 0, Math.PI * 2);
        ctx.fillStyle = n % 2 ? '#7cc4f2' : '#3f8fd2';
        ctx.fill();
      }
      ctx.globalAlpha = 1;
    }

    /* 维度参数演示用的淹没面 */
    if (typeof opt.threshold === 'number') {
      var levelY = y1 - (y1 - y0) * (0.15 + opt.threshold / 400);
      var flood = [[x0, y0], [x1, y0], [x1, levelY], [x0, levelY]].map(px);
      ctx.beginPath();
      ctx.moveTo(flood[0][0], flood[0][1]);
      for (var q = 1; q < flood.length; ++q) {
        ctx.lineTo(flood[q][0], flood[q][1]);
      }
      ctx.closePath();
      ctx.globalAlpha = 0.45;
      ctx.fillStyle = '#2f74c0';
      ctx.fill();
      ctx.globalAlpha = 1;
    }

    ctx.strokeStyle = 'rgba(90, 105, 120, 0.25)';
    ctx.lineWidth = 1;
    ctx.strokeRect(0.5, 0.5, w - 1, h - 1);
  }

  function synthToURL(w, h, bbox, opt) {
    var canvas = document.createElement('canvas');
    canvas.width = Math.max(1, Math.round(w));
    canvas.height = Math.max(1, Math.round(h));
    synthDraw(canvas.getContext('2d'), canvas.width, canvas.height, bbox, opt);
    return canvas.toDataURL('image/png');
  }

  function synthWmsTile(tile, src, opt) {
    var bbox = synthParam(src, 'BBOX').split(',').map(Number);
    var w = parseInt(synthParam(src, 'WIDTH'), 10) || 256;
    var h = parseInt(synthParam(src, 'HEIGHT'), 10) || 256;
    if (bbox.length === 4) {
      tile.getImage().src = synthToURL(w, h, bbox, opt);
    }
  }

  function synthWmsImage(image, src, opt) {
    var bbox = synthParam(src, 'BBOX').split(',').map(Number);
    var w = parseInt(synthParam(src, 'WIDTH'), 10) || 512;
    var h = parseInt(synthParam(src, 'HEIGHT'), 10) || 512;
    if (bbox.length === 4) {
      image.getImage().src = synthToURL(w, h, bbox, opt);
    }
  }

  function synthExtent(source, tile) {
    var coord = tile.getTileCoord();
    return coord && source.getTileGrid() ? source.getTileGrid().getTileCoordExtent(coord) : null;
  }


  function capabilitiesXml() {
    var head = '<Capabilities xmlns="http://www.opengis.net/wmts/1.0" ' +
      'xmlns:ows="http://www.opengis.net/ows/1.1" version="1.0.0">' +
      '<ows:ServiceIdentification><ows:Title>演示 WMTS 服务</ows:Title>' +
      '<ows:ServiceType>OGC WMTS</ows:ServiceType>' +
      '<ows:ServiceTypeVersion>1.0.0</ows:ServiceTypeVersion>' +
      '</ows:ServiceIdentification><Contents>' +
      '<Layer><ows:Title>演示区县</ows:Title>' +
      '<ows:Identifier>demo:districts</ows:Identifier>' +
      '<Style isDefault="true"><ows:Identifier>default</ows:Identifier></Style>' +
      '<Format>image/png</Format>' +
      '<TileMatrixSetLink><TileMatrixSet>EPSG:3857</TileMatrixSet></TileMatrixSetLink>' +
      '<ResourceURL format="image/png" resourceType="tile" ' +
      'template="https://demo.invalid/wmts/demo:districts/default/EPSG:3857/' +
      '{TileMatrix}/{TileRow}/{TileCol}.png"/>' +
      '</Layer><TileMatrixSet><ows:Identifier>EPSG:3857</ows:Identifier>' +
      '<ows:SupportedCRS>urn:ogc:def:crs:EPSG::3857</ows:SupportedCRS>';

    var matrices = '';
    for (var z = 0; z <= 12; ++z) {
      matrices += '<TileMatrix><ows:Identifier>' + z + '</ows:Identifier>' +
        '<ScaleDenominator>' + (559082264.0287178 / Math.pow(2, z)) +
        '</ScaleDenominator>' +
        '<TopLeftCorner>-20037508.3427892 20037508.3427892</TopLeftCorner>' +
        '<TileWidth>256</TileWidth><TileHeight>256</TileHeight>' +
        '<MatrixWidth>' + Math.pow(2, z) + '</MatrixWidth>' +
        '<MatrixHeight>' + Math.pow(2, z) + '</MatrixHeight></TileMatrix>';
    }

    return head + matrices + '</TileMatrixSet></Contents></Capabilities>';
  }

  var result = new ol.format.WMTSCapabilities().read(capabilitiesXml());
  var options = ol.source.WMTS.optionsFromCapabilities(result, {
    layer: 'demo:districts',
    matrixSet: 'EPSG:3857'
  });

  options.tileLoadFunction = function (tile) {
    var extent = options.tileGrid.getTileCoordExtent(tile.getTileCoord());
    tile.getImage().src = synthToURL(256, 256, extent, {
      palette: ['#a9c9ec', '#b7dbb2', '#efcf9f', '#e8aabf', '#bdafd9', '#9ed0c9']
    });
  };

  var wmtsSource = new ol.source.WMTS(options);

  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}),
      new ol.layer.Tile({source: wmtsSource, opacity: 0.85})
    ],
    view: new ol.View({
      center: ol.proj.fromLonLat([116.391, 39.907]),
      zoom: 9
    })
  });

  document.getElementById('info').textContent =
    '图层 demo:districts · 矩阵集 EPSG:3857 · 分辨率 ' +
    options.tileGrid.getResolutions().length + ' 级';

})();
</script>
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