Table of Contents: Coverages & Datacubes: the Big Picture Synopsis Coverage specifications (with adoption status) Abstract Models (conceptual level) Concrete Coverage Model (logical level) Coverage Data Model Coverage Service Model Coverage Data and Request Encodings (physical level) Coverage Format Encodings Coverage Service Protocol Bindings Non-Coverage documents Technical Coverage resources

Coverages & Datacubes:
the Big Picture

This page gives an overview of the coverage data and service model, in particular the WCS service suite. Datacubes form a special type of coverages which continues to receive particular attention.

Synopsis

Figure: Coverage data and service model overview

Coverage specifications (with adoption status)

All coverage-related adopted standards - in particular: the CIS and WCS suites - can be found on the OGC WCS page, except for the WCPS language definition which is maintained separately for historical reasons.

Standards are grouped along the common IT abstraction hierarchy:

• conceptual level: terminology and concepts
• logical level: interoperable data and service specifications
• physical level: specific encodings

Note: In the past, the distinction between these levels has not been made sufficiently clear in the standards. Often concepts were directly expressed in GML (more recently, in JSON) rather than separating them cleanly. In recent years, more attention has been paid at least in the WCS suite so the more recent standards split into separate documents (ex: ISO 19123-1 and 19123-2) or at least have separate conformance classes (ex: WCS service functionality vs request/response encoding).

Abstract Models (conceptual level)

Standards on this level of abstraction define concepts and terminology of coverage data and processing (not concrete data encodings and services). ISO 19123-1 replaces ISO 19123:2005.

• Abstract coverage data model:
  • ISO 19123-1:2023 Geographic information — Schema for coverage geometry and functions — Part 1: Fundamentals
  • = OGC Topic 6.1 - Schema for coverage geometry and functions - Part 1: Fundamentals

• Abstract coverage processing model:
  • ISO 19123-3:2023 Geographic information — Schema for coverage geometry and functions — Part 1: Processing Fundamentals
  • = OGC Topic 6.3 - Schema for coverage geometry and functions - Part 1: Processing Fundamentals (note: there is no 6.2, numbering has been chosen in sync with ISO 19123 numbering)

Concrete Coverage Model (logical level)

Coverage Data Model

• Coverage Implementation Schema (CIS), version 1.1 document and schemas for XML, JSON, RDF and examples: (adopted, backwards compatible next version of CIS 1.0); key features (see rationales):
  • ISO TC211 is currently preparing an integration of CIS 1.0 and 1.1 into a single specification, together with further improvements. Currently, the draft package is under submission for DIS ballot. An XML and JSON schema draft package is uploaded for preview with the caveat that this is not normative and may still change. OGC might re-adopt this as CIS 1.1.
  • CIS 1.1 is backwards compatible to CIS 1.0, and so does not require any change to WCS 2 (just a formal extension to allow WCS instances serve the new coverage types - accomplished by WCS 2.1).
    
  • CIS 1.1 adds class GeneralGridCoverage which is simplified and more powerful than the legacy CIS 1.0 grid distinction of Rectified / Referenceable Grid. Instead, grids are described through various axis types: non-referenced, regular, irregular, etc; these axis types can be combined arbitrarily in a coverage (eg, regular, rectified Lat and Long axes together with an irregular time axis).
  • support for alorithmically defined grids via integration of SensorML 2.0
  • coverages can be partitioned while still acting as one (eg, in a WCS GetCoverage request)
  • support for XML, JSON, and RDF
• Coverage Implementation Schema - ReferenceableGridCoverage Extension, OGC 16-083r2: adopted extension to CIS 1.0
  • This standard closes a gap of GML 3.2.1 inherited by CIS 1.0 which has left ReferenceableGridCoverage underspecified. While CIS 1.1 GeneralGridCoverage encompasses the concept of ReferenceableGridCoverages some stakeholders requested to specifically provide this coverage type. Therefore, this standard has been crafted as an extension to CIS 1.0.
• Coverage Implementation Schema (CIS), version 1.0.1 document and schema, OGC 09-146r2: adopted

Coverage Service Model

• Web Coverage Service (WCS):
  • WCS Core, version 2.1.0 document and schema and examples, OGC 17-089: adopted (no change/update of functionality over WCS Core 2.0.1 - only needed to allow CIS 1.1 coverages)
  • service extensions:
    • WCS Interface Standard - Range Subsetting Extension, version 1.0.0, OGC 12-040: adopted
    • WCS Interface Standard - Scaling Extension, version 1.0.0, OGC 12-039: adopted
    • WCS Interface Standard - CRS Extension, version 1.0.0, OGC 11-053: adopted
    • WCS Interface Standard - Interpolation Extension, version 1.0.0, OGC 12-049: adopted
    • WCS Interface Standard - Processing Extension, version 2.0.0, OGC 08-059r4: adopted
    • WCS Interface Standard - Transaction Extension, version 2.0.0, OGC 13-057: adopted
    • WCS Extension - Web Query Service, version 1.0.0, OGC 14-121: on hold as per OAB as it might go into OWS Common (which never happened as OWSCommon got abandoned)
  • WCS Application Profiles:
    • WCS 2.0 Interface Standard - Earth Observation Application Profile (EO-WCS), version 1.0, OGC 10-140: adopted
    • WCS 2.0 Interface Standard - Earth Observation Application Profile (EO-WCS), version 1.1, OGC 10-140r2: adopted
    • WCS Application Profile - MetOcean ("MetOcean-WCS") Part 0 - MetOcean Metadata (OGC 15-045r7) and Part 1 - MetOcean GetCorridor Extension (OGC 15-108r3) and Part 2 - MetOcean GetPolygon Extension (OGC 17-086r3) version 1.0.0: adopted
  • Coverage & Datacube Analytics:
    • Web Coverage Processing Service (WCPS) Language Interface Standard
      • version 1.1.0 OGC 08-068r3: adopted Interface Standard
      • version 1.0.0, OGC 08-068r2: adopted Interface Standard
  • Coverage data / metadata integration:
    • Web Query Service (WQS) 1.0, OGC 14-121 Best Practice
    • see also WCPS 1.1
• OAPI-Coverages: work in progress, based on WCS concepts
  • based on OGC CIS
  • basically duplicates WCS functionality but CAVEAT with slight deviations making it incompatible.
  • For details, see this overview on OAPI-Coverages and its relation to WCS
• GeoDataCubes: initial-stage

Coverage Data and Request Encodings (physical level)

On this level, concrete interoperable and conformance-testable data structures are defined, based on the conceptual and logical schemas.

Coverage Format Encodings

• GML Application Schema - Coverages - GeoTIFF Coverage Encoding Profile, version 1.0, OGC 12-100r1: adopted
• GML Application Schema - Coverages - JPEG2000 Coverage Encoding Profile, version 1.0, OGC 12-108: adopted
• CF-netCDF 3.0 encoding using GML Coverage Application Schema, version 2.0, OGC 14-100r2: adopted
• GRIB2 Encoding Profile: under adoption vote
• JPIP Coverage Encoding Profile: activities commenced, but stalled - looking for activists

Notes:

• as there are known bugs in OWS Common 2.0 which never got fixed, WCS inherits those. This can lead to known validation issues in responses such as from GetCapabilities requests.
• Due to limitations in GML, only numerical coordinates are allowed. This is insufficient, e.g., with temporal axes where common date notations as per ISO 8601 (like "2022-10-02T15:33") are required. While coverages commonly use such date formats for time coordinates this will lead to XML validation errors. GML has not signalled to enhance its coordinate representations. Therefore, CIS 1.1 departs from GML in some aspects, like coordinates, thereby avoiding these issues.

Coverage Service Protocol Bindings

• WCS Interface Standard - KVP Protocol Binding Extension, version 1.0.1, OGC 09-147r3: adopted
• WCS Interface Standard - POST/XML Protocol Binding Extension, version 1.0.0, OGC 09-148r1: adopted
• WCS Interface Standard - SOAP Protocol Binding Extension, version 1.0.0, OGC 09-149r1: adopted
• WCS Interface Standard - REST Protocol Binding Extension, version 1.0.0, OGC 12-174: under discussion

Non-Coverage documents

• CRS Name Type Specification, version 1.0.0, OGC 11-135r2: adopted
• WPS Application Profile - Coverages, version 2.0.0, OGC 09-045r1, adopted Discussion Paper

Technical Coverage resources

• OGC WCS schema location -- normative
• ISO EA UML model -- normative
• Testbed-11 Engineering Report motivating CIS 1.1, OGC 15-065r1