While there are some circumstances in which altitude is required (e.g., Operation volumes), they are should not always be required (e.g., when querying for Subscriptions). So, the component definition of Volume3D should not make these fields required, and instead the usage of the encompassing Volume4D should specify in its description when these fields are required or not.
While there are some circumstances in which altitude is required (e.g., Operation volumes), they are should not always be required (e.g., when querying for Subscriptions). So, the component definition of Volume3D should not make these fields required, and instead the usage of the encompassing Volume4D should specify in its description when these fields are required or not.