Demystifying OGC APIs with GeoServer: introduction and status of implementation Ing. Andrea Aime GeoSolutions 

GeoSolutions Enterprise Support Services Deployment Subscription Professional Training Customized Solutions GeoNode • Offices in Italy & US, Global Clients/Team • 40+ collaborators, 30+ Engineers • Our products • Our Offer 

Affiliations We strongly support Open Source, it Is in our core We actively participate in OGC working groups and get funded to advance new open standards We support standards critical to GEOINT 

A bit of history 

At the beginning, there was WFS3 • First commit July 31st 2017 • Developed in the repo for a bunch of months, then various public events shaped it into OGC API - Features WFS3 Hackaton Testbed 14 Vector Tiles Pilot Testbed 15 API Hackaton London 

API Hackaton, London 2018 • The same Web API approach as WFS3 is extended to other APIs, as well as having a shared core API Commons Features Coverages Maps & Tiles Processes Catalogs Styles More! 

Periodic OGC API Sprints • Since then OGC organized periodic code sprints • Each sprint focuses on 2-3 specs and: ○ Push forward specification drafts ○ Implement and gather feedback ○ Test interoperability • GeoSolutions participates to push GeoServer API implementations forwards 

Up to 2022: releases and drafts • Released: ○ OGC API - Features ■ Core (Sept 2019) ■ CRS by Reference (Oct 2020) ○ OGC API - Environmental Data Retrieval (March 2021) ○ OGC API - Processes (August 2021) • Most APIs and extensions are still in draft stage and changing 

OGC API - Common elements 

OGC APIs - OpenAPI • Fresh take on spatial data interoperability • Based on OpenAPI/RESTful concepts • Resource/representation • HTTP verbs • Small core, a basic service can be implemented in a matter of days • Extensions for every other functionality 

OGC API (OAPI) Common • Can be found at: https://github.com/opengeospatial/oapi_common • Resources: • / (landing page) • /conformance (conformance classes implemented) • For services exposing data: • /collections • /collection/{collectionId} • OpenAPI definition linked from landing page with rel service-desc 

Links, links everywhere! • All resources are linked to the others, in the various encodings: /collections /collections/{collectionId} Backlinks to self and alternative representations (different formats/encodings) Links to each collection in each of its formats { "href":"http://data.example.org/collections.json", "rel":"self", "type":"application/json", "title":"this document" } 

Resource representations • OAPI Commons recommends: ○ HTML for humans and crawlers ○ JSON for machine to machine • Choose: ○ Accept header ○ Custom query param (“f” is a common choice) 

Extensions and conformance • Tiny core, bare minimum for a working service • Modular extensions for everything else • Find what is supported using conformance declaration 

Features API Core 

Features API Core • In addition to OAPI core: • /collection/{collectionId}/items (features) • /collection/{collectionId}/items/{itemId} • Only supported CRS are • CRS84 (WGS84 lon/lat) • CRS84h (WGS84 lon/lat/height) • Schema not required, features can be anything: • Simple • Complex • Heterogeneous • “describeBy” can link to schema (optional) 

OpenAPI definition 

/collection/{collectionId}/items • Lists the contents of a collection • Can be a GeoJSON document, GML, anything • Filtering • bbox in CRS84 or CRS84h • datetime (instant or range of times) • extra parameters declared in the API document (only by equality, not supported by GS) …/collections/buildings/items? bbox=41,54,42,55 &datetime=2018-02-12T23%3A20%3A52Z &buildingState=good 

Paging • limit query parameter • A limit is always present (like in WFS 1.x and 2.x) but can be high • Paging works through links, "prev" and "next" rel values • Links can be implemented the way you want • GeoServer uses offset as an extra paging parameter [ { "href":"http://example.org/collections/buildings/items.json?limit:50", "rel":"prev", "type":"application/geo+json" }, { "href":"http://example.org/collections/buildings/items.json?limit:50&offset:50", "rel":"self", "type":"application/geo+json" }, { "href":"http://example.org/collections/buildings/items.json?limit:50&offset:100", "rel":"next", "type":"application/geo+json" } ] 

CORE: that’s all folks! • Yes ladies and gentlemen, this is everything OGC API - Features - CORE covers 

Wait wait wait…. • Look that's nice, but what about…. 

Part 2 - CRS by Reference • Support CRS other than CRS84 • Discover: ○ Storage (native) CRS ○ Supported target CRS • Parameters: ○ bbox-crs (query) ○ crs (reproject) ● Finalized! ● GeoServer currently implements older draft 

Part 3 - Filtering (draft) ● Queryables: properties that can be used for filtering ○ May be a sub-set of the actual attributes ○ May not even match the attributes (e..g, like “anyText” in CSW) ● filter: the filter specification ● filter-lang: the language used ● filter-crs: the CRS for the geometries used in the filter ● cql2-text, cql2-json ● GeoServer supports also ecql-text (classic GeoServer extended CQL) 

CQL2 encodings (draft) eo:cloud_cover BETWEEN 0.1 AND 0.2 AND landsat:wrs_row=28 AND landsat:wrs_path=203 { "and": [ { "between": [ {"property": "eo:cloud_cover"}, 0.1, 0.2 ] }, { "=": [{"property": "landsat:wrs_row"},28] }, { "=": [{"property": "landsat:wrs_path"},203] } ] } &filter-lang=cql2-text &filter-lang=cql2-json 

CQL2 encodings support in GeoServer ● Initially it was slightly modified CQL, quite similar to ECQL. Supported! ● First round of CQL-JSON in Sept 2020 ● In Sept 2021, CQL2, with significant changes ○ cql2-text support landed Feb 2021 ○ cql2-json parsing March 2022 ○ cql2-json encoding June 2022 ● CQL2 is still changing (last change, Aug 2nd 2022) 

Sorting ● Not part (yet) of OGC API - Features ● Part of “proposals” not yet turned into draft extensions ● Borrowed from OGC API - Records ● Available in GS 2.22 and 2.21 /items?sortby=name,-dateOfBirth 

Property selection ● Not part (yet) of OGC API - Features ● Not implemented in GeoServer ● Part of “proposals” not yet turned into draft extensions ● returnables, parallel to queryables, list properties that can be selected ● properties to enumerate wanted properties ● skip-geometry to avoid geometry field ● STAC API has a different take: fields ● Use “-” to remove a property, e.g. fields=geometry,-links,-assets&f=json 

Part 4 - CRUD transactions in draft ● Create/Replace/Update/Delete for single feature ● Currently in draft ● Not currently supported by GeoServer .../collections/topp:states/items/states.1 POST PUT DELETE PATCH 

OGC Features API GeoServer HTML representations 

Features API landing page DEFAULT TEMPLATES FULLY CUSTOMIZABLE 

Features API /api 

Collections /collections 

Collection /collections/{collectionId} 

Items /collections/{collectionId}/items 

Coverages 

OGC APIs - Coverages • The simplest WCS ever? • Collection as a single coverage • GeoServer implementation is currently incomplete 

Coverage and its components • DomainSet: spatial and temporal domain description • RangeType: data structure (bands and types) • RangeSet: the actual pixels • Metadata: any other info about the coverage DomainSet + RangeType + RangeSet + Metadata = ----------- Coverage Coverage Implementation Schema (JSON encoding) 

Coverage extraction • Core allows to extract data from a coverage by: • bbox • datetime ...collections/nurc:Img_Sample/coverage? f=image%2Fpng& bbox=-130,20,-100,40 

Missing bits • The GeoServer implementation lacks the following: • RangeSet resource → describes bands • Range subsetting → band selection • Scaling scale-size/scale-factor/scale-axes • Coverage tiles 

Maps 

Maps API • Draft available at https://github.com/opengeospatial/ogcapi-maps • Building block to produce maps, can be attached to collections, but in general, to any resource that can be mapped • Adds a notion of a “style”, listed in collection metadata • Adds a “maps” resource • GetFeatureInfo not in core! 

“map” resource • Fetches a map in the requested format • Params: width, height, bbox, crs, …. • Unlike WMS GetMap, all params are optional → similar to the GeoServer WMS reflector .../ogc/maps/collections/topp:states/styles/population/map?f=image/png 

“info” resource (GS specific) • Not part of the standard (used to be in a previous draft) • Still useful (considers scale deps, filters, symbology) • Feature info at given location • Params: “i/j” mandatory, others same as “map” .../ogc/maps/collections/topp:states/styles/population/map/info? f=text/plain&i=50&j=10 Results for FeatureType 'http://www.openplans.org/topp:states': -------------------------------------------- the_geom = [GEOMETRY (MultiPolygon) with 276 points] STATE_NAME = Washington STATE_FIPS = 53 SUB_REGION = Pacific STATE_ABBR = WA LAND_KM = 172447.205 WATER_KM = 12226.63 PERSONS = 4866692.0 FAMILIES = 1264934.0 HOUSHOLD = 1872431.0 MALE = 2413747.0 FEMALE = 2452945.0 WORKERS = 1830031.0 DRVALONE = 1700872.0 CARPOOL = 282240.0 PUBTRANS = 104403.0 EMPLOYED = 2293961.0 UNEMPLOY = 139216.0 -------------------------------------------- 

Tiles 

Tiles API • Available at https://github.com/opengeospatial/ogcapi-tiles • Still evolving, GeoServer not up to date • Adds resources for tiles, tile matrix sets, eventually styles • Tiles can be styled or not (e.g. tiling maps or tiling data) 

Building block, can tile “anything” ● /collections/{collectionId} 🡪 data tiles from single collection ● /collections/{collectionId}/maps 🡪 rendered tiles from single map ● /collections 🡪 raw tiles from multiple collections (list of collections as query param) ● /map 🡪 tiles from multi-layer map (list of collections as query param) ● /add/your/own/here 🡪 if it can be sliced, we'll tile it 

Tiles resource, URL templates ogc/tiles/collections/topp%3Astates/styles/population/map/tiles/ WebMercatorQuad/{tileMatrix}/{tileRow}/{tileCol}?f=image%2Fpng 

Tiles “metadata” resource ● Extension provided by some implementations ● Describes the tiles contents ● Can return TileJSON (GeoServer does) { "tilejson": "2.2.0", "name": "topp:states" , "description" : "This is some census data on the states." , "scheme": "xyz", "tiles": [ ".../ogc/tiles/collections/topp%3Astates/tiles/WebMercatorQuad/{z}/{y}/{x}?f=mvt ], "center": [ -89.99999997494392 , 42.525564403512014 , 1.0 ], "bounds": [-124.731422 , 24.955967, -66.969849, 49.371735 ], "format": "application/vnd.mapbox-vector-tile" , "minzoom": 0, "maxzoom": 24, "vector_layers" : [ { "id": "states", "description" : "This is some census data on the states." , "fields": { "STATE_NAME" : "string", "STATE_FIPS" : "string", "HOUSHOLD": "number" ... 

Styles 

Styles API • Building block to describe styles for a resource • In GeoServer a stand-alone API 

Style transformation • If the server supports it, fetch a style in various encodings (GeoServer can do CSS 🡪 SLD, MBStyle 🡪 SLD, YSLD 🡪🡪 SLD) A stylesheet can be marked as “native” SLD 1.0 core SLD 1.1 core YSLD extension MBStyles community GeoCSS extension SLD 1.0 inspired object model, with extensions 

Style metadata Basic metadata info (yeah, I did not fill it yet, no love lost for metadata!) Access to style source, native (CSS) and converted (SLD) when possible List of layers involved in the style (could have many) and attributes used in each (style editor can use them to check compatibility with available data) The style identifier 

Styles API client • "Visual style editor" as developed by GeoSolutions in Testbed 15 

And more 

More of APIS! • More APIS supported by GeoServer: • STAC API • DGGS/DAPA (Data Access and Processing API) • Images (mosaic management) • More APIs NOT supported by GeoServer yet: • Records (CSW) • Processes (WPS) • Routes (WPS specific for routing) • Environmental Data Retrieval 

That’s all folks! Questions? [email protected] 

That’s all folks! Questions? [email protected]