How to define tileset position in cesium - cesiumjs

Question

I am trying to explore cesium 3d tileset. but I did not find a way to position tileset.
I tried transformation and bounding volumes in tileset.json but that wont work.
{
"asset": {
"version": "1.0"
},
"properties": {
"Height": {
"minimum": 20,
"maximum": 20
}
},
"geometricError": 70,
"root": {
"refine": "ADD",
"transform": [
1.0001,0,0,
0,1,0,0,
0,0,1,0,
0,0,0,1
],
"boundingVolume": {
"region": [
-1.3197004795898053,
0.6988582109,
-1.3196595204101946,
0.6988897891,
0,
30
]
},
"geometricError": 0,
"content": {
"uri": "instancedOrientation.i3dm"
}
}
}

Answer 1

I found how to position tileset in cesium.
Just change translation in transform matrix
tileset = cviewer.scene.primitives.add(new Cesium.Cesium3DTileset({
url : url
}));
//Original location of tileset
let pos = {
x: 1214939.1184933728,
y: -4736505.884059093,
z: 4081598.457967,
};
tileset._root.transform[12] = cviewer.camera.position.x - pos.x;
tileset._root.transform[13] = cviewer.camera.position.y - pos.y;
tileset._root.transform[14] = cviewer.camera.position.z - pos.z;

Answer 2

I recently had to do this but I also needed a rotation and a scale.
Here's a demo
And the code
It seems that today, the correct way to transform a tileset in cesium is through the tileset.modelMatrix
Here's the function that calculates the transformation matrix given lon/lat/height coordinates, a rotation and a scale with the correct matrix multiplication order:
function computeTransformationMatrix(lon, lat, height, rotation, scale) {
const location = Cesium.Cartesian3.fromDegrees(lon, lat, height);
const translationMatrix = Cesium.Transforms.eastNorthUpToFixedFrame(location);
const scaleMatrix = Cesium.Matrix4.fromScale(scale)
const rotationMatrixX = Cesium.Matrix3.fromRotationX(rotation.x);
const rotationMatrixY = Cesium.Matrix3.fromRotationY(rotation.y);
const rotationMatrixZ = Cesium.Matrix3.fromRotationZ(rotation.z);
const rotation3 = new Cesium.Matrix3();
Cesium.Matrix3.multiply(rotationMatrixZ, rotationMatrixY, rotation3);
Cesium.Matrix3.multiply(rotationMatrixX, rotation3, rotation3);
const rotationMatrix = Cesium.Matrix4.fromRotation(rotation3);
const matrix = new Cesium.Matrix4();
Cesium.Matrix4.multiply(translationMatrix, scaleMatrix, matrix);
Cesium.Matrix4.multiply(matrix, rotationMatrix, matrix);
return matrix;
}