So what is a coverage? Coverages are the worldwide accepted concept for representing raster data, used by OGC, ISO, and INSPIRE (they can also represent point clouds and general meshes, but typically focus is on raster).
The coverage data model: A coverage consists of a domain set ("where are the data located?"), a range set (the pixel payload), a range type ("what is the semantics of these data?)", and some arbitrary metadata ("what else should I know about these data?"). Both OGC and ISO agree on an interoperable coverage definition with broad format encoding support.
The coverage service model: The OGC Web Coverage Service (WCS) standards suite esablishes a structured, modular collection of service standards. WCS Core deins the basic functionality: coverage download, subsetting, and format encoding. Any implementation claiming to support WCS must support this - very basic - Core functionality. A set of optional WCS extensions enhances services with additional facets, up to the geo datacube analytics and fusion language, Web Coverage Processing Service (WCPS).
OGC OAPI-Coverage: Currently an effort is underway to unify OGC feature, coverage, map, and processing services based on the OpenAPI concepts. From a WCS perspective, this is an evolution, not a disruptive replacement: first, the new OAPI-Coverage specification is based on the OGC Coverage Implementation Schema (CIS) 1.1. Second, effort is devoted to maintain coherence - OAPI-Coverage from a WCS perspective should resemble just another "protocol binding" which can be used interchangeably with GET/KVP, POST, and SOAP.
The OGC/ISO Coverage ecosystem: The coverage data and service model, including OAPI-Coverage, form a powerful, versatile ecosystem of coverage functionality. The following diagram shows the complete WCS suite with its components and their relationships:
Conformance testing: OGC provides a rigorous conformance test suite validating implementations down to pixel level.
Coverage standards: The authoritative source for coverage data is the OGC Coverage Implementation Schema, which is also ISO standard (ISO 19123-2:2018). Further definitions, such as by W3C or definitions solely relying on the abstract model of ISO 19123, are not authoritative, not interoperability-proven, not as rigorously implementation-tested as OGC CIS is, and not with the multitude of implementations supporting it. OGC/ISO coverages can be served via OGC WCS/WCPS (which has the most dedicated coverage functionality), but also via OGC WMS, WPS, and SOS.
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