There are standards to represent geospatial data in the context of linked data, such as GeoSPARQL. However, I could not find a way to represent the coordinates that are not on Earth - such as, for example, coordinates of Moon objects. I.e., I need somehow to express the fact that the coordinate is not on Earth and provide a reference to what the coordinate refers to. Is there any standard that deals with that?
According to this paper, you can specify the crs using a url like http://www.opengis.net/def/crs/EPSG/0/4326 , where the last bit is the EPSG code. You can also look for OGC crs codes using a similar URL.
I don't know SPARQL, but you might be able to query all the available EPSG and OGC codes from that.
EPSG coordinate systems were originally developed for oil and gas exploration, and as far as I know we don't much of that off-world ;)
There are coordinate reference systems for a number of planetary bodies, under IAU2000 (e.g. 30100 for the Moon) and you can find their definitions here. The proj4 string for the Moon, for example, is
+proj=longlat +a=1737400 +b=1737400 +no_defs
You might want to look at Virtuoso, they appear to have some proj4 extensions to geosparql, which might allow you to assign a custom crs using a custom proj4 string.
The declaration in RDF Triples of such an idea may be like :
PREFIX geo:<http://www.opengis.net/ont/geosparql#> <object_URI> geo:hasGeometry <object_geometry_URI> <object_geometry_URI> geo:asWKT "<http://www.opengis.net/def/crs/OGC/1.3/CRS84> POINT (1.0 2.0)"^^xsd:wktLiteral
object_URI is your actual object and
object_geometry_URI represents the geometry object defining the geometry of the
There is absolutely not problem to change the CRS (Be aware to reproject your data if you do so).