OGC API – Features Part 3 handles enhanced filtering: a fundamental operation performed on a collection of features in order to obtain the subset of the data that’s relevant to your workflow.

The Open Geospatial Consortium (OGC) seeks public comment on the candidate OGC API – Features – Part 3: Filtering and the Common Query Language (CQL) standard, which extends the Core Part of OGC API – Features to support data filtering. Comments are due by April 19, 2021.

OGC API – Features provides API building blocks to create, modify, and query features on the Web. The spatial data community uses the term “feature” for things in the real world that are of interest. For more information on what a ‘feature’ is, see the explanations on Spatial Things, Features, and Geometry in the W3C/OGC Spatial Data on the Web Best Practice document.

OGC API Features is comprised of multiple parts, each a separate standard. Part 1: Core specifies the core capabilities and is restricted to fetching features where geometries are represented in the coordinate reference system WGS 84 with axis order longitude/latitude. Part 2: Coordinate Reference Systems by Reference extends the Core with the ability to use coordinate reference system identifiers other than the defaults defined in the core.

This standard, part 3, handles enhanced filtering: a fundamental operation performed on a collection of features in order to obtain the subset of the data that’s relevant to your workflow. 

As such, part 3 of the OGC API – Features Standard defines:

• Query parameters (filter, filter-lang, filter-crs) to specify filter criteria in a request to an API;
• A filter grammar called Common Query Language (CQL) for specifying enhanced filtering criteria beyond what is supported in the Core;
• Two encodings for CQL – a text and a JSON encoding.

In a geospatial data processing workflow, OGC API – Features – Part 3 allows a web call to define a subset of data hosted in the cloud to be used by, say, a processing API (such as OGC API – Processes), or a web or desktop application for analysis or display. Other OGC API standards like OGC API – Records or OGC API – Tiles will reuse the filtering building blocks to allow filtering on records in a catalog or features in vector tiles.

The candidate OGC API – Features – Part 3: Filtering and the Common Query Language (CQL) standard is available for review and comment on the OGC Portal. Comments are due by April 19, 2021, and should be submitted via the method outlined on the OGC API – Features – Part 3 Standard’s public comment request page.

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