1. Linking Big Data from Space to Apps on Earth
Location Powers: Big Linked Geodata workshop
Colocated with the 102nd OGC Technical Committee
Delft, The Netherlands
Uwe Voges (con terra GmbH,
22 March 2017
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Problems
Start summarizing problems of end-user / app- developer less experienced with Geo services wanting to find and use EO data
Finding EO data (ideally as online service) via Google & Co not easy:
Result: general info, news, pictures (NASA),…
Needs to search specific EO portals
EO data often not online -> stored in archives
user has to regis- ter -> try to find, order, download the data
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Problems
Data delivered as huge datasets, requiring preprocessing,…
If online services exist (e.g. OGC based view, download, MD) …
client has to deal with different URI´s, offering different service interfaces
need to construct specific service calls
client cannot just “follow links” (-> HATEOAS)
Data / services described by specific metadata models (ISO, O&M..)
not providing common encodings, not using common vocabularies
objects often re-modeled instead of linking to existing representations
prevents (meta)data being part of a wider network
cannot be indexed by Google & Co or Open Data Portals
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Targets
Reliable, performant and easy web accessible EO data services
Easy REST-based data-access and visualization services
Download of Online Data in different formats (incl metadata)
ideally cloud based
Example going in this direction: AGOL providing REST-based ArcGIS Image Services (also providing WMS/WCS)
Finding EO data services via Google & Co or Open Data Portals
To become indexed: need for commonly understood metadata
Based on Resource Description Framework (RDF) – using common vocabularies / ontologies
E.g provided as annotated (schema.org) HTML pages
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5. Metadata Approach: LOD/RDF
Linked Open Data (LOD) is based on RDF
Elements identified by URLs, can directly be looked up
Links to other URLs by using concepts of common vocabularies which provide their semantic
(Geo)DCAT-AP, schema.org, FOAF, EUROVoc, OGC (EOP)..
Links allow navigation to related things and minimize replications
RDF Encoding e.g. in XML or JSON-LD (optimized for client consumption)
Can be stored in RDF-store for which standard query language exists: (Geo)SparQL
Open Data Portals often provide both and allow harvesting of RDF
JSON-LD can provide RDF data (e.g. datasets, OpenSearch results or semantic annotations of HTML pages)
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6. REST-API for data / metadata access
web developer friendly REST API would be important
download, map view, annotated HTML, metadata (RDF/JSON) etc of EO resource -> just from one single base URL
Example: EOP Resource (URI): <root>/Collections/{Coll-ID}/Products/{Product-ID}
Div representations available using different mimeTypes / format parameters:
Download: application/octet-stream
Metadata: application/ld+json -> provides JSON-LD EOP metadata (OGC ) incl links to collection etc
HTML: text/html -> describing EOP incl preview, download URL, URL to collection (HATEOS). Annotated with schema.org
WMS: application/vnd.ogc.wms_xml, link to Capabilities / getMap
Some resources e.g. <root>/Collections/{Coll-ID} provide query support -> OSDD for conformant search ->JSON-LD
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7. Limited Example: Online Data Provision
Simple Use Case:
weather conditions during forest fire in Portugal based on three EUMETSAT SEVIRI products :00
High Rate SEVIRI Level 1.5 Image Data-MSG
Multi-Sensor Precipitation Estimate (GRIB)
Active Fire Monitoring (GRIB) - MSG (presence of fire within a pixel)
Derived buffer surrounding fires
Data loaded into ArcGIS mosaic datasets and published with ArcMap as ArcGIS Image REST Service and OGC WMS/WCS)
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8. Limited Example: Metadata Indexing & Search
Services (not data) described with RDF metadata (using GeoDCAT-AP, EuroVoc, INSPIRE and FOAF)
Harvested into test version of new EU Data Portal (EDP), running RDF store
During ingestion every RDF description gets assigned a URL
Via this URL the metadata can be accessed in RDF, or annotated HTML
Annotated HTML indexed by Google
targeted searches using vocabularies spatio-temporal filters, etc not possible
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9. Limited Example: Metadata Indexing & Search
In EDP the services can be searched and discovered via UI and GeoSparQL.
much more targeted searches (facetted) possible
based on categories, tags, key- words, boundingBox, format, etc.
EDP is based on Virtuoso RDF store, allowing SparQL queries
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10. Limited Example: Online Data Access
From search results it´s possible to open the EDP map client which loads the associated WMS
Client is based on conterra map.apps: able to interpret GeoDCAT-AP and to identify the WMS access point
Result entries pointing to ArcGIS Image Services can be used by a proper client (e.g. ArcMap) for visualization, applying on the fly processing, or downloading image parts
a: SEVIRI
b: a+Fire
c: a+b+ Precipitation estimation -> incl. download options
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11. Questions to be answered
RESTful Service Interfaces needed
Which vocabularies to use
Not suitable for EO data, currently no standard for EO Data -> OGC under development -> (Geo)JSON-LD
Flexible enough (!) descriptions of service bindings:
In a perfect REST world it is much easier
But we have different service interfaces, protocol bindings, fileCompression, service description, parameter definitions, formats,…
owc:offerings -> used in EO metadata (17-003) -> limited to some use cases
Defined already ideas for a description of service access in DCAT
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