WMS Time

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function threeHoursAgo() {
  return new Date(Math.round(Date.now() / 3600000) * 3600000 - 3600000 * 3);
}

var extent = ol.proj.transformExtent([-126, 24, -66, 50], 'EPSG:4326', 'EPSG:3857');
var startDate = threeHoursAgo();
var frameRate = 0.5; // frames per second
var animationId = null;

var layers = [
  new ol.layer.Tile({
    source: new ol.source.Stamen({
      layer: 'terrain'
    })
  }),
  new ol.layer.Tile({
    extent: extent,
    source: new ol.source.TileWMS({
      attributions: ['Iowa State University'],
      url: 'https://mesonet.agron.iastate.edu/cgi-bin/wms/nexrad/n0r-t.cgi',
      params: {'LAYERS': 'nexrad-n0r-wmst'}
    })
  })
];
var map = new ol.Map({
  layers: layers,
  target: 'map',
  view: new ol.View({
    center: ol.extent.getCenter(extent),
    zoom: 4
  })
});

function updateInfo() {
  var el = document.getElementById('info');
  el.innerHTML = startDate.toISOString();
}

var stop = function() {
  if (animationId !== null) {
    window.clearInterval(animationId);
    animationId = null;
  }
};

var play = function() {
  stop();
  animationId = window.setInterval(setTime, 1000 / frameRate);
};

var startButton = document.getElementById('play');
startButton.addEventListener('click', play, false);

var stopButton = document.getElementById('pause');
stopButton.addEventListener('click', stop, false);

updateInfo();

<!DOCTYPE html>
<html>
  <head>
    <title>WMS Time</title>
    <link rel="stylesheet" href="https://openlayers.org/en/v4.6.4/css/ol.css" type="text/css">
    <!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
    <script src=""></script>
    <script src="https://openlayers.org/en/v4.6.4/build/ol.js"></script>
  </head>
  <body>
    <div id="map" class="map"></div>
    <div role="group" aria-label="Animation controls">
      <button id="play" type="button">Play</button>
      <button id="pause" type="button">Pause</button>
      <span id="info"></span>
    </div>
    <script>
      function threeHoursAgo() {
        return new Date(Math.round(Date.now() / 3600000) * 3600000 - 3600000 * 3);
      }

      var extent = ol.proj.transformExtent([-126, 24, -66, 50], 'EPSG:4326', 'EPSG:3857');
      var startDate = threeHoursAgo();
      var frameRate = 0.5; // frames per second
      var animationId = null;

      var layers = [
        new ol.layer.Tile({
          source: new ol.source.Stamen({
            layer: 'terrain'
          })
        }),
        new ol.layer.Tile({
          extent: extent,
          source: new ol.source.TileWMS({
            attributions: ['Iowa State University'],
            url: 'https://mesonet.agron.iastate.edu/cgi-bin/wms/nexrad/n0r-t.cgi',
            params: {'LAYERS': 'nexrad-n0r-wmst'}
          })
        })
      ];
      var map = new ol.Map({
        layers: layers,
        target: 'map',
        view: new ol.View({
          center: ol.extent.getCenter(extent),
          zoom: 4
        })
      });

      function updateInfo() {
        var el = document.getElementById('info');
        el.innerHTML = startDate.toISOString();
      }

      function setTime() {
        startDate.setMinutes(startDate.getMinutes() + 15);
        if (startDate > Date.now()) {
          startDate = threeHoursAgo();
        }
        layers[1].getSource().updateParams({'TIME': startDate.toISOString()});
        updateInfo();
      }
      setTime();

      var stop = function() {
        if (animationId !== null) {
          window.clearInterval(animationId);
          animationId = null;
        }
      };

      var play = function() {
        stop();
        animationId = window.setInterval(setTime, 1000 / frameRate);
      };

      var startButton = document.getElementById('play');
      startButton.addEventListener('click', play, false);

      var stopButton = document.getElementById('pause');
      stopButton.addEventListener('click', stop, false);

      updateInfo();
    </script>
  </body>
</html>