Orienting Models

I have been trying to get a model into cesium using Model.fromGltf. I can get the model in but don’t understand how to orient it and haven’t been able to find any help. I don’t understand how modelMatrix works. How can I orient an object based off a position and direction in ECEF coordinates? I’ve tried Tranforms.rotationMatrixFromPositionVelocity like this:

const position = Cartesian3.fromDegrees(lon, lat, .altitude);
const velocity = new Cartesian3(velocity_x, velocity_y, velocity_z)


  url: 'model/scene.gltf',

  modelMatrix: Transforms.rotationMatrixFromPositionVelocity(position, velocity),

  scale: 5000.0,


I would expect that to place the model at the position and orient it according to the velocity but it stretches the object so it is essentially a line through Earth about 4x as long as earth’s diameter.

Any help would be appreciated. Thanks

This forum discussion might help:

Specifically the next to last post has an example of how to use rotationMatrixFromPositionVelocity.