How to define property type in SampledProperty in Cesium

问题

I am using Cesiumjs to create a polygon which is moving around an area.

To show its movement I tried to create a sampledPropertyof PolygonHierarchy. Each sample is an array of Cartesian3 positions (three endpoints of my polygon at each time step).

I need to know the type of the property that I am using in sampledProperty as it is mentioned in Cesiumjs website: Cesiumjs.org/SampledProperty.

But I don't know how to define it and I couldn't find any explanation on the website on how to identify property type especially when each sample by itself is an array of properties.

回答1:

The SampledProperty doesn't work here, since it attempts to interpolate smoothly between the points you've given it, and it doesn't know how to interpolate a polygon hierarchy.

So instead, you can use a TimeIntervalCollectionProperty. The difference here is that this property animates by steps, not interpolation, so the property does not need to know how to construct the intermediate values between control points.

I made a small demo, to show how this works with a polygon hierarchy. Click Run Code Snippet at the bottom, or copy-and-paste just the JavaScript into Sandcastle.

var viewer = new Cesium.Viewer('cesiumContainer', {
    navigationInstructionsInitiallyVisible: false
});

// Set up a limited range of time for this demo.
var time = Cesium.JulianDate.fromIso8601('2016-04-08T12:00:00Z');
viewer.clock.clockRange = Cesium.ClockRange.LOOP_STOP;
viewer.clock.startTime = time;
viewer.clock.currentTime = time;
viewer.clock.stopTime = Cesium.JulianDate.addSeconds(time, 20, new Cesium.JulianDate());
viewer.clock.multiplier = 1;
viewer.timeline.updateFromClock();
viewer.timeline.zoomTo(time, viewer.clock.stopTime);

// Construct a TimeIntervalCollection showing the changes to the hierarchy over time.
var hierarchy = new Cesium.TimeIntervalCollectionProperty();

for (var i = 0; i < 40; ++i) {
    var nextTime = Cesium.JulianDate.addSeconds(time, 0.5, new Cesium.JulianDate());

    // Inside the loop, per iteration we add one window of time for this polygon.
    hierarchy.intervals.addInterval(new Cesium.TimeInterval({
        start: time,
        stop: nextTime,
        isStartIncluded : true,
        isStopIncluded : false,
        data : Cesium.Cartesian3.fromDegreesArrayHeights([-108.0+i/4, 35.0, 100000,
                                                          -100.0+i/4, 35.0, 100000,
                                                          -100.0+i/4, 40.0, 100000,
                                                          -108.0+i/4, 40.0, 100000])
    }));
    
    time = nextTime;
}

// Create the polygon, using the animated hierarchy.
var orangePolygon = viewer.entities.add({
    name : 'Orange polygon with time-varying position',
    polygon : {
        hierarchy : hierarchy,
        extrudedHeight: 0,
        perPositionHeight : true,
        material : Cesium.Color.ORANGE.withAlpha(0.5),
        outline : true,
        outlineColor : Cesium.Color.WHITE
    }
});

viewer.zoomTo(viewer.entities);

html, body, #cesiumContainer {
  width: 100%; height: 100%; margin: 0; padding: 0; overflow: hidden;
  font-family: sans-serif;
}

<link href="http://cesiumjs.org/releases/1.19/Build/Cesium/Widgets/widgets.css" 
      rel="stylesheet"/>
<script src="http://cesiumjs.org/releases/1.19/Build/Cesium/Cesium.js">
</script>
<div id="cesiumContainer"></div>

来源：https://stackoverflow.com/questions/36538973/how-to-define-property-type-in-sampledproperty-in-cesium

标签

javascript

polygon

cesium