Sky direction representation

For both the control system as well processing we need to ensure that we are able to represent entities such as sky directions in a way that ensures:

• Minimum likelihood that we will get inconsistencies in interpretation
• A good coverage of all possible use cases

The latter should cover not just what we need right now (i.e. see ADR-54), as for processing we need to make potentially wide-ranging decisions about what kind of processing we might possibly be able to do. So we need to also think about potential future use cases, possibly even involving SRCs.

Why now? Processing function library data models are starting to get locked down

Qualities: Modifiability, Extensibility, Flexibility, Performance?