Rotate Camera Around Transform At Fixed Angle

CesiumJS
1

Hi,
I would like to fix the angle that the camera looks at a certain spot so that the user can only rotate left and right around the point without any up or down movement of the camera.

var transform = Cesium.Transforms.eastNorthUpToFixedFrame(Cesium.Cartesian3.fromDegrees(-122.22, 46.12));

var heading = Cesium.Math.toRadians(180.0);

var pitch = Cesium.Math.toRadians(-35.0);

var range = 50000.0;

viewer.camera.lookAtTransform(transform, new Cesium.HeadingPitchRange(heading, pitch, range));

This is my code right now, so I would like to keep the camera at the 35-degree angle.

Thank you.