CZML data source - GTLF model disappears a certain camera angles

Hi all

I am seeing my model disappears at certain camera angles when it is close to the ground. I’ve read related posts about similar problems with 3Dtiles


pointing the problem to be the bounding volume. Is it possible to change the bounding volume of a gltf file?

I also tried to set debugShowBoundingVolume: true in the model, but the boundingVolume does not show.

Here is a zip of a screen recording
model disappears.mp4.zip (2.5 MB)

My CZML

[

{
  id: "document",
  name: "CZML Path",
  version: "1.0",
  clock: {
    interval: `${begin}/${end}`,
    currentTime: begin,
    multiplier: 1,
  },
},
{
  id: "path",
  availability: `${begin}/${end}`,
  debugShowBoundingVolume: true,
  path: {
    material: {
      polygon: {
        color: {
          rgba: [255, 0, 255, 255],
        },
      },
    },
    width: 2,
    leadTime: 1,
    resolution: 1,
  },
  model: {
    id: "airplane",
    gltf: "./Cessna_172.gltf",
    debugWireframe: true,
    color: Cesium.Color.RED,
    debugShowBoundingVolume: true,
    nodeTransformations: {
      RootNode: {
        rotation: {
          unitQuaternion: [0, 0.7071, 0, 0.7071],
        },
      },
    },
  },
  viewFrom: {
    cartesian: [70, 20, 30], //
  },
  position: {
    interpolatitudeionAlgorithm: "LAGRANGE",
    interpolatitudeionDegree: 1,
    cartographicDegrees: [....],
  },
  orientation: {
    unitQuaternion: [....],
  },
},

];

Thanks in advance.

The bounding volume issue shouldn’t apply here if you’re loading your model directly as a glTF, and not as a 3D Tileset I believe.

Are you able to share a Cesium scene with this model? You can upload it (along with the CZML) to your Cesium ion account and then share a link here. See: https://cesium.com/docs/tutorials/import-3d-models/

Hi @omar, myself and @Emanuel_Herrmann have looked a bit deeper into this issue after the Christmas break and been able to reproduce this from the sandcastle code playground.

We were able to replicate the bug with both our own model and the model from the sandcastle. After this we tried hard coding the altitude to 0 in the datasource and found the issue was resolved, this lead us to log out the terrains metadata with sampleTerrainMostDetailed(terrainProvider, positions) and we think that the terrain tiles at in that area are rendering at a different hight that the metadata is reporting which is around 22 meters below sea level.

Sandcastle: https://tinyurl.com/y6t4onyd