材质控制：material
var redTube = viewer.entities.add({
name : 'Red tube with rounded corners',
polylineVolume : {
positions : Cesium.Cartesian3.fromDegreesArray([-85.0, 32.0,-85.0, 36.0,-89.0, 36.0]),
shape : computeCircle(6000.0),
//颜色回调
material : new Cesium.ColorMaterialProperty(new Cesium.CallbackProperty(function() {
return Cesium.Color.fromRandom({
minimumRed : 0.75,
minimumGreen : 0.75,
minimumBlue : 0.75,
alpha : 1.0
});
}, false))
}
});
