HeightLimited

Example:

var pnts = [
    new Cesium.Cartesian3(115.03481079096245, 27.007844388021834, 0.0),
    new Cesium.Cartesian3(115.03481079096245, 27.006646020977758, 0.0),
    new Cesium.Cartesian3(115.03610070479618, 27.006646020977758, 0.0),
    new Cesium.Cartesian3(115.03610070479618, 27.007844388021834, 0.0)
];

var heightLimited = new Cesium.HeightLimited(viewer,{
    height: 0.0,
    limitedColor: new Cesium.Color(1, 0, 0, 0.5),
    polygonColor: Color.WHITE.withAlpha(0.7),
    blendTransparency: 0.8,
    posArray: pnts
});
// 添加限高
heightLimited.add();
// 移除限高
heightLimited.remove();