Coverage standards

Coverages are fully standardized by the OGC (Open Geospatial Consortium):

• Abstract, high-level definitions are laid down in OGC Abstract Topic 6 which is identical to ISO 19123 Geographic information — Schema for coverage geometry and functions. This standard is currently being reworked into 19123–1 Geographic information — Schema for coverage geometry and functions — Part 1: Fundamentals.
• Concrete, interoperable definitions are given in the OGC Coverage Implementation Schema (CIS), which is adopted by ISO as 19123–2 Geographic information — Schema for coverage geometry and functions — Part 2: Coverage implementation schema.

Several versions of the OGC Coverage Implementation Schema (CIS):

CIS 1.0, formerly known as “GML 3.2.1 Application Schema – Coverages”, and nicknamed GMLCOV; as this name caused considerable confusion in the community, OGC in 2015 decided to rename the standard to Coverage Implementation Schema (CIS) – hence, GMLCOV 1.0 and CIS 1.0 are synonymous.

CIS 1.0 introduces three different coverage types: 

• GridCoverage: historically the first approach to gridded coverages - Not recommended today because of limitations in the way coordinates can be expressed.
• RectifiedGridCoverage: historically the next approach, aiming at regular grids such as orthoimagery.
• ReferenceableGridCoverage: originally, it was meant to capture “all other sorts of grids”, but its definition was left blank in GML 3.2.1 and was never edited into the standard despite a corresponding change request adopted by OGC. Therefore, an extension specification to CIS 1.0 was established which provides an according definition for some irregular grid types.

CIS 1.1, which presents a more “tidy” and comprehensible schema providing consistency compared with its previous antecesors. It defines a model (GeneralGridCoverage type) generalizing the capabilities of GML 3.2.1 and 3.3, CIS 1.0, and SensorML 2.0 grid concepts as a result of a comprehensive study on grid coverages  undertaken as part of OGC Testbed-11. 

CIS 1.1 General Grid Coverage definition allows cases not addressed by any of the other mentioned approaches, ultimately allowing the description of any multi-dimensional grid, with space, time, or any other semantics (such as spectral bands). The main difference is that it does not differentiate grid types like the predecessor standards, but considers different axis types from which grids can be composed.