Need help! Clipping 3Dtileset with real world coordinates clipping plane failed

I have an entity called this box, and I want to use it to clip geometry of a model. It works fine when I have not defined modelMatrix. I looked up the clipping plane example and there it says can use real-world coordinates to define the clipping extent with modelMatrix. But in my case when its defined with this_box, the building Tile just disappears.


I want to apply this and make a part of a larger 3Dtileset disappear - eg. knowing the coordinates of a building / site area and make it disappear . Many Thanks!

Code below…

const position = Cartesian3.fromDegrees(114.20870458148214, 22.319308777310678, 10)
// an entity called this box to clip the 3d tile with clipping plane
const this_box = viewer.entities.add({
position: position,
box: {
dimensions: new Cartesian3(70.0, 70.0, 100.0), material: Color.WHITE.withAlpha(0.3),
outline: true,
outlineColor: Color.WHITE,
var clippingPlanes1 = [
new ClippingPlane(new Cartesian3(0.0, -1.0, 0), -10)

//add building tileset
const newBuildingTileset = await Cesium3DTileset.fromIonAssetId(2359136);

newBuildingTileset.clippingPlanes = new ClippingPlaneCollection({
modelMatrix: this_box.computeModelMatrix(,
planes : clippingPlanes1,
edgeWidth :5,
edgeColor: Color.RED,
enabled: true,