How to set the camera using the orientation

CesiumJS
1

I add a frustum ,it has an orientation property.I use the orientation to get headingpitchroll,I set
the camera

scene.camera.flyTo({
destination:positionOnEllipsoid,
orientation:Cesium.HeadingPitchRoll.fromQuaternion(orientation)
})

but I find the camera is wrong