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<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta
      name="viewport"
      content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no"
    />
    <meta
      name="description"
      content="Use Viewer to start building new applications or easily embed Cesium into existing applications."
    />
    <meta name="cesium-sandcastle-labels" content="Beginner, Showcases" />
    <title>Cesium Demo</title>
    <script type="text/javascript" src="../Sandcastle-header.js"></script>
    <script
      type="text/javascript"
      src="../../../Build/CesiumUnminified/Cesium.js"
      nomodule
    ></script>
    <script type="module" src="../load-cesium-es6.js"></script>
  </head>
  <body
    class="sandcastle-loading"
    data-sandcastle-bucket="bucket-requirejs.html"
  >
    <style>
      @import url(../templates/bucket.css);
    </style>
    <div id="cesiumContainer" class="fullSize"></div>
    <div id="loadingOverlay"><h1>Loading...</h1></div>
    <div id="toolbar"></div>
    <script id="cesium_sandcastle_script">
      function startup(Cesium) {
        "use strict";
        //Sandcastle_Begin
        // This example illustrates a Callback Property, a property whose
        // value is lazily evaluated by a callback function.
        // Use a CallbackProperty when your data can't be pre-computed
        // or needs to be derived from other properties at runtime.
        var viewer = new Cesium.Viewer("cesiumContainer");
        viewer.clock.shouldAnimate = true;

        var startLatitude = 35;
        var startLongitude = -120;
        var endLongitude;
        var startTime = Cesium.JulianDate.now();

        // Add a polyline to the scene. Positions are dynamic.
        var isConstant = false;
        var redLine = viewer.entities.add({
          polyline: {
            // This callback updates positions each frame.
            positions: new Cesium.CallbackProperty(function (time, result) {
              endLongitude =
                startLongitude +
                0.001 * Cesium.JulianDate.secondsDifference(time, startTime);
              return Cesium.Cartesian3.fromDegreesArray(
                [startLongitude, startLatitude, endLongitude, startLatitude],
                Cesium.Ellipsoid.WGS84,
                result
              );
            }, isConstant),
            width: 5,
            material: Cesium.Color.RED,
          },
        });

        var startCartographic = Cesium.Cartographic.fromDegrees(
          startLongitude,
          startLatitude
        );

        // use scratch object to avoid new allocations per frame.
        var endCartographic = new Cesium.Cartographic();
        var scratch = new Cesium.Cartographic();
        var geodesic = new Cesium.EllipsoidGeodesic();

        // Calculate the length of the line
        function getLength(time, result) {
          // Get the end position from the polyLine's callback.
          var endPoint = redLine.polyline.positions.getValue(time, result)[1];
          endCartographic = Cesium.Cartographic.fromCartesian(endPoint);

          geodesic.setEndPoints(startCartographic, endCartographic);
          var lengthInMeters = Math.round(geodesic.surfaceDistance);
          return (lengthInMeters / 1000).toFixed(1) + " km";
        }

        function getMidpoint(time, result) {
          // Get the end position from the polyLine's callback.
          var endPoint = redLine.polyline.positions.getValue(time, result)[1];
          endCartographic = Cesium.Cartographic.fromCartesian(endPoint);

          geodesic.setEndPoints(startCartographic, endCartographic);
          var midpointCartographic = geodesic.interpolateUsingFraction(
            0.5,
            scratch
          );
          return Cesium.Cartesian3.fromRadians(
            midpointCartographic.longitude,
            midpointCartographic.latitude
          );
        }

        // Label the polyline with calculated length.
        var label = viewer.entities.add({
          position: new Cesium.CallbackProperty(getMidpoint, isConstant),
          label: {
            // This callback updates the length to print each frame.
            text: new Cesium.CallbackProperty(getLength, isConstant),
            font: "20px sans-serif",
            pixelOffset: new Cesium.Cartesian2(0.0, 20),
          },
        });

        // Keep the view centered.
        viewer.trackedEntity = label;
        //Sandcastle_End
        Sandcastle.finishedLoading();
      }
      if (typeof Cesium !== "undefined") {
        window.startupCalled = true;
        startup(Cesium);
      }
    </script>
  </body>
</html>

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