csiroenvinf/geometry-data-service repository overview

⁠Geometry data service

The Geometry Data Service (GDS) is a lightweight API that has been developed for serving RESTful geometries over the web. In particular, these were the functions the GDS provides:

• minting URIs for geometries to enable Linked Data functionality
• content-negotiation for formats and representations of the geometry
• search by point for relevant geometries across the geometry store
• parameterise the profile of the geometry representation for a Loc-I Feature (geometry of a feature with a resolution in metres, bounding box, centroid, simplified vs. complex geom, projection/CRS)

The current Geometry Data Service uses the pyLDAPI⁠ to implement the Linked Data APIs.

⁠Quickstart

$ cd api
$ virtualenv venv
$ source venv/bin/activate
$ pip install -r requirements.txt
$ export FLASK_APP=app.py
$ export FLASK_ENV=development
$ flask run --port=3000 --host=0.0.0.0

Specify env variables for the db connection

$ export GSDB_DBNAME=gis
$ export GSDB_HOSTNAME=localhost
$ export GSDB_PORT=5432
$ export GSDB_USER=jon
$ export GSDB_PASS=jon

Once flask is running, go to http://localhost:3000⁠ and use links provided

⁠Deploy using docker

An alternative to the simple flask run is via docker.

You can use the Docker Hub image at https://hub.docker.com/r/csiroenvinf/geometry-data-service⁠.

$ docker pull csiroenvinf/geometry-data-service

$ docker run --name gservice -d -p 3000:3000 csiroenvinf/geometry-data-service 

Or with environment variables

$ docker run  -e GSDB_DBNAME=gis -e GSDB_HOSTNAME=localhost -e GSDB_PORT=5432 -e GSDB_USER=user -e GSDB_PASS=pass -p 3000:3000 --network host -it csiroenvinf/geometry-data-service 

⁠Scope

⁠Mint URIs for geometries and provide an API for it

• Only store (geo-referenced) geometries
• Scoped to Earth initially

Implies

• Ability to embed a URI Reference in a Loc-I feature instance
• Selecting a predicate to associate a feature with the geometry URI reference (GeoSPARQL or something else?)
• Returning the geometry representation from somewhere (from a remote service or local geodatabase cache)
• Content negotiation by profiles

⁠Out of scope

Performing extensive utility calculations on geometries (i.e. ArcGIS GeometryService⁠).

⁠Content negotiation interfaces

The Geometry Data Service implements and extends conneg arrangement proposed by (Regalia et al. 2017). Conneg interfaces the GDS implements are shown below:

GDS also implements some content profiles (refer to W3C Conneg by Profile⁠):

The combination of the two sets of interfaces allows users to query for the geometry resource to suit the needs of the application.

⁠Usage scenarios

⁠Linking from a description of a feature

Rather than embed a literal to the geometry in the Geosparql Feature instance, we can use the GDS to mint a URI for the geometry and bind it via a URI.

Example: ASGS 2016 Meshblock Feature

<http://linked.data.gov.au/dataset/asgs2016/meshblock/20663970000> a asgs:MeshBlock,
        geo:Feature ;
    geo:hasGeometry <http://gds.loci.cat/dataset/asgs16_mb/20663970000> ;
.

It is up to the client/user to resolve the URI ref to the Geometry via standard HTTP plus conneg (by profile and format).

⁠Find the respective feature(s) from the geometry

Given a geometry description, we can follow links back to respective geometry. An example of the RDF/Turtle format response for the Geometry URI http://gds.loci.cat/geometry/asgs16_mb/20663970000:

<http://gds.loci.cat/geometry/asgs16_mb/20663970000> a geo:Geometry,
        sf:MultiPolygon ;
    geox:isGeometryOf <http://linked.data.gov.au/dataset/asgs2016/meshblock/20663970000> .

We can then traverse back to the Feature via the value for the geox:isGeometryOf property.

⁠References and related work

• https://gnis-ld.org/⁠
• Regalia et al., Revisiting the Representation of and Need for Raw Geometries on the Linked Data Web, LDOW, 2017, http://ceur-ws.org/Vol-1809/article-04.pdf⁠