ISO 19162 restricts compound CRS to the following components in that order:
- A mandatory horizontal CRS (only one of two-dimensional GeographicCRS or ProjectedCRS or EngineeringCRS)
- Optionally followed by a VerticalCRS or a ParametricCRS (but not both).
- Optionally followed by a TemporalCRS.
SIS currently does not enforce those restrictions. In particular:
- Components may appear in different order.
- VerticalCRS + TemporalCRS (without horizontal component) is accepted.
- GeocentricCRS or three-dimensional GeographicCRS can be combined with TemporalCRS.
We should nevertheless perform a check and raise a flag if the CRS does not meet WKT restrictions, even if we still format it.