Coordinate Reference System (CRS) definitions as coordinate systems related to the earth through datum. An explanation for this package is provided in the OpenGIS® javadoc. The remaining discussion on this page is specific to the SIS implementation.

The root class for this package is Abstract­CRS. Coordinate Reference System (CRS) can have various number of dimensions, but some restrictions apply depending on the CRS type:

Common Coordinate Reference System types
Dimension CRS type examples Remarks
3 Geographic, Geocentric ISO 19111 uses the same class, Geodetic­CRS, for those two cases.
2 Geographic, Projected GeographicCRS can also be 3D.
1 Vertical, Temporal.
Any Compound Often used for adding a time axis to the above CRS.

Apache SIS extensions

Some SIS implementations provide additional methods that are not part of OGC/ISO specifications: In addition Apache SIS provides two distinct classes for geographic and geocentric CRS where OGC/ISO defines a single Geodetic­CRS type. OGC/ISO distinguishes the geographic/geocentric cases according the type of the coordinate system associated to that CRS: SIS keeps the geographic and geocentric CRS as distinct types since such distinction is in wide use.