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An effective good practice to boost interoperable provision of (raster) INSPIRE Coverage data and services: Revision

What is a coverage?

A coverage is a unifyed paradigm for modelling and encoding raster data of all kind, from 1D sensor timeseries, over 2D raster images, up to spatio-temporal datacubes. 
It describes spatio-temporal regular and irregular grids (i.e., multi-dimensional datacubes), point clouds, and general meshes.

In plain words coverage are modelled like a function, composed by the following elements:

  • Domain set, answering “at what coordinates can I find values?” (the domain of the function). 
  • Range set, determining “what are the values?” (the image set of the function). 
  • Range type, informing "which are the basic characteristics of the values?". It is utilised to capture the full semantics of the values in the coverage. 
  • Optional metadata bucket, carrying any additional information that may be also relevant for users.

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The range type of a coverage is also an standardized description based on the SWE (Sensor Web Enablement) Common (http://www.opengeospatial.org/standards/swe) concepts.  

This allows sensor data to be transformed into coverages without information loss, thereby enabling seamless service chains from upstream data acquisition (e.g., through OGC SOS) to downstream analysis-ready user services (such as OGC WMS, WCS, and WCPS). 

Such coverages can be represented in a variety of shapes – including tilings, coordinate/value pair lists – and formats - such as GML, JSON, RDF, a variety of binary encodings, as well as “containers” with mixed encodings. Hence, tools can request coverages in their favourite format from a server.

Coverage standards

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

  • At abstract, conceptual level, in OGC Abstract Topic 6 which is identical to ISO 19123
  • At concrete, interoperable level in the OGC Coverage Implementation Schema (CIS), which is adopted by ISO as 19123–2.

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

CIS 1.0, formerly known as “GML 3.2.1 Application Schema – Coverages” (GMLCOV).

CIS 1.1, which provides a comprehensive, more consistent schema for grid coverages.

Find here more details on coverage standardisation.

Use of coverages in INSPIRE

Coverages are widely used in different thematic domains in the scope of the INSPIRE Directive:

  • Annex II: Elevation (EL), Land cover (LC), Orthoimagery (OI), Geology (GE);
  • Annex III: Soil (SO), Land use (LU), Natural risk zones (NZ), Environmental Monitoring Facilities (EF), Atmospheric conditions (AC), Meteorological geographical features (MF), Oceanographic geographical features (OF), Energy resources (ER), Species Distribution (SD);

However, two different approaches are used by INSPIRE themes to serve coverage data to the user:

1. WCS view: Coverages are considered as features (i.e. INSPIRE FeatureTypes in these themes are based on Coverage Classes).

Regular or irregular grids are used by the WCS view INSPIRE themes.

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2. SOS view: Coverages are considered as observation results.

Regular or irregular grids are used by the SOS view INSPIRE themes.

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Which is the main issue about INSPIRE coverages?

 

Good Practice: Proposal for an interoperable solution

A coverage service for various (raster data) INSPIRE themes has been setup to overcome these issues as a result of the related activities performed in the scope of the INSPIRE Community Forum (Thematic Clusters) during the last years, particularly based on the results from the Workshop “Feel the power of INSPIRE WCS / WCPS in your hands” organised in the INSPIRE Helsinki 2019 Technical Conference:

“INSPIRE Coverages Demystified”http://inspire.rasdaman.org/

The demo service allows the user to play with different service requests to get INSPIRE coverage data and metadata, analyse and combine different data layers (cross-theme fusion), download and present the final results. 

It is specially designed to demonstrate use of coverages and WCS/WCPS for several INSPIRE themes: Elevation, Orthoimagery and Land cover - The service is powered by the rasdaman WCS reference implementation and offers sample data from a regional data provider (Institut Cartogràfic i Geològic de Catalunya, ICGC).

The objectives are to:

  • Experience the potential of these technologies.
  • Fully-understand the main benefits of integrating them within their daily geospatial businesses and analytical tasks.

...but mainly:

  • Get feedback from the community on this functional good practice to align INSPIRE coverages to OGC standards, by amending in a simple, OGC compliant way the INSPIRE XSD coverage schemas (as INSPIRE coverage metadata).

Provide your feedback

A related discussion thread has been open in the Software & Tools group of the INSPIRE Community Forum for this purpose:

https://inspire.ec.europa.eu/forum/discussion/view/265095/inspire-coverages-demo-service

Find more details about preliminary analysis

  • Article “INSPIRE coverages: an analysis and some suggestions”:

https://link.springer.com/article/10.1186/s40965-019-0059-x

 

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