Add MD_ReferenceSystemTypeCode or document its equivalence

[desruisseaux]

The MD_ReferenceSystemTypeCode code list defined by ISO 19115-1 is currently not transposed in GeoAPI. That code list has been excluded in current draft because the same functionality can be achieved in the Java language with instanceof statements. For example:

Equivalence for MD_ReferenceSystemTypeCode.projected:

crs instanceof ProjectedCRS

Equivalence for MD_ReferenceSystemTypeCode.geodeticGeographic2D:

crs instanceof GeographicCRS &&
crs.getCoordinateSystem().getDimension() == 2

Equivalence for MD_ReferenceSystemTypeCode.compoundProjectedTemporal:

crs instanceof CompoundCRS &&
crs.getComponents().size() == 2 &&
crs.getComponents().get(0) instanceof ProjectedCRS &&
crs.getComponents().get(1) instanceof TemporalCRS

etc. Admittedly those equivalences can become complicated. Despite that equivalences exist, we should probably not rely on them and introduce the missing MD_ReferenceSystemTypeCode. Descriptions of that code list can be seen there:

• CSIRO Linked Data Registry
• Earth Science Information Partners (ESIP)