I initially removed the RectangularPyramidSensorVolume because rectangular sensors can be directly rendered with CustomSensorVolume. SensorVolumeCollection was removed because sensor volumes are primitives that can be added directly to the scene’s primitive collection.
I’ve updated the cesium-sensors repository with changes that re-add the RectangularPyramidSensorVolume class for convenience, and I added another example that demonstrates creating the sensor primitives directly via the API, rather than simply using CZML.