use GeoSPARQL instead of osgeo

[VladimirAlexiev]

https://github.com/isawnyu/pleiades-rdf#user-content-ordnance-survey-ontology states " extents of spatial objects are expressed using osgeo:AsGeoJSON, and osgeo:AsWKT" where osgeo is http://data.ordnancesurvey.co.uk/ontology/geometry/. This is confirmed by http://atlantides.org/capgrids/2.ttl that uses props osgeo:asGeoJSON, osgeo:asWKT.
There are 2 flaws with this approach:

• http://data.ordnancesurvey.co.uk/ontology/geometry/ (specifically http://www.ordnancesurvey.co.uk/ontology/geometry.owl) doesn't include such properties. It has only osgeo:asGML
• to my knowledge no semantic repositories implement indexing of such osgeo properties.

Please use the GeoSPARQL standard that is implemented by at least 4-5 repositories (GraphDB, Virtuoso, uSeekM, Strabon...). Eg

@prefix geo: <http://www.opengis.net/ont/geosparql#> .
<http://example.org/1/geometry>
        geo:asWKT "<http://www.opengis.net/def/crs/OGC/1.3/CRS84>POLYGON ((-3.70 40.42, ...))"^^geos:wktLiteral.
<http://example.org/2/geometry>
        geo:asWKT "<http://www.opengis.net/def/crs/EPSG/0/23030> POLYGON ((439930.8579 4475096.6375, ...))"^^geo:wktLiteral.

(examples from openlink/virtuoso-opensource#455).

Note:

• You must tag the literals with datatype ^^geo:wktLiteral
• You must indicate the CRS in the literal, unless it's http://www.opengis.net/def/crs/OGC/1.3/CRS84, which is the default. You can find more OGC-defined CRS starting at http://www.opengis.net/def/crs/OGC

Unfortunately GeoSPARQL doesn't define a property asGeoJSON. I don't know of an ontology to define such property officially. But just using osgeo:asGeoJSON that is not defined is not good. As @ewg118 wrote in https://groups.google.com/forum/#!topic/pelagios-project/QAyZw__8pDg 4 years ago: "Is asGeoJSON a proposed property that doesn't exist in the stable ontology yet? If not, can the property be incorporated into the pleiades ontology? As it is, our data are floating out in semantic purgatory."

So define it in pleiades.

[ewg118]

There are still one or two examples of GeoJSON polygons encoded into the osgeo:asGeoJSON property in Nomisma. This has come up recently on the linked.art slack channel. The asGeoJSON property is still not in the Ordnance Survey ontology, which does not even appear to be actively maintained anymore. It would be extremely useful to have some sort of property for encoding the GeoJSON as a literal, as GeoJSON support is more broad than WKT at this point.

[ewg118]

What about adding a property into the GeoJSON-LD ontology itself, @sgillies? Such as geojson:featuresLiteral

[sgillies]

@ewg118 it's a good idea, but I can't reopen GeoJSON-LD for revision any time soon.

[ewg118]

Is there anything to do other than updating the RDF ontology and the documentation pages?

[sgillies]

Two more things at least, @ewg118:

• update PURL records
• write to relevant lists for comments and 👍 or 👎

[VladimirAlexiev]

Adding an opaque geojson literal would be great since structured geojson-ld doesn't capture lists properly