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:
- Abstract coverage processing model:
Concrete Coverage Model (logical level)
Coverage Data Model
- Coverage Implementation Schema (CIS), version 1.2 pending, identical to ISO IS and XML schema and JSON schema, both with ample examples. Key features:
- CIS 1.2 is an integration of CIS 1.0, CIS 1.1, and the Referenceable Grid Extension, hence backwards compatible (also with WCS 2)
- more tbd
- 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):
- 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:
- Coverage & Datacube Analytics:
- Web Coverage Processing Service (WCPS) Language Interface Standard
- Coverage data / metadata integration:
- OAPI-Coverages: work in progress, based on WCS concepts
- 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
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
Non-Coverage documents
Technical Coverage resources