Problems in display of 3D-Points

1. A concise explanation of the problem you're experiencing.

My Poincloud is moved to sky when choose a DTM or vice versa.

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

Display of 3DTiles according the sandcastle - maybe no Problem with Software but with data ?

tileset.json:
{
  "asset": {
    "version" : "0.0"
  },
  "geometricError": 5,
  "root" : {
    "refine" : "ADD",
    "boundingVolume": {
      "sphere": [
      4105618.592310839,
      824370.9880344045,
      4795516.828308291,
      100
      ]
    },
    "geometricError": 0,
    "content": {
      "url": "points.pnts"
    }
  }
}

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

Display 3D-Pointcloud with/without Terrain Information ?

4. The Cesium version you're using, your operating system and browser.
1.40, Windows, chrome

Cesium doesn’t clamp tilesets to terrain so the point cloud will stay fixed in space while different terrain providers may appear above or below it. But you can adjust a tileset’s height by editing its modelMatrix. See http://localhost:8080/Apps/Sandcastle/?src=3D%20Tiles%20Adjust%20Height.html&label=3D%20Tiles.