# Modeling Geometry and Reference Systems on the Web of Data

Raphaël Troncy, Ghislain Auguste Atemezing, Nathalie Abadie

► To cite this version:

Raphaël Troncy, Ghislain Auguste Atemezing, Nathalie Abadie. Modeling Geometry and Reference Systems on the Web of Data. Linking Geospatial Data Workshop, Dec 2014, Londres, United Kingdom. hal-02398638

HAL Id: hal-02398638

https://hal.science/hal-02398638

Submitted on 7 Dec 2019

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Modeling Geometry and Reference Systems on
the Web of Data

Raphaël Troncy<fnref n="1" />, Ghislain A. Atemezing<fnref n="1" /> and Nathalie Abadie<fnref n="2" />

**Abstract.** For many years now, the web of data has been dominated with the use of only one Coordinate System (CRS), namely WGS84, to represent the localization of geographic objects on Earth. Reasons for its adoption is the simplicity of the vocabulary (few core classes and properties) and the fact that the vocabulary is described in a W3C namespace. Nowadays, with the Open Data movement, more and more publishers including governments and local authorities are releasing legacy data that is often geolocalized in a different coordinate system. For example, IGN in France in releasing data that is geolocalized using Lambert93, a Lambert conformal conic projection (LCC) when objects are localized on the France metropolitan area. In this paper, we propose two vocabularies that take into account geometries defined in different coordinate systems. We provide as well mappings with existing vocabularies to ensure compatibilities with existing implementations. Finally, we provide a REST service that supports the conversion of coordinates between several CRS.

**Keywords:** Ontology modeling, Geographic data, Coordinate systems, Geometry vocabulary, Linked Data, REST service

## 1 Identification and Description of CRS

The EPSG registry<fnref n="3" /> identifies various coordinates systems. The Open Geospatial Consortium (OGC) recommends to use URI to identify coordinate reference systems under the uri http://www.opengis.net/def/crs/. For example, the WGS84 coordinate system is identified by OGC with http://www.opengis.net/def/crs/OGC/1.3/CRS84 while the authority EPSG will identify CRS under the uri http://www.opengis.net/def/crs/EPSG/0/4326.

In France, the National Geographic Institute (IGN) is also maintaining a registry of several coordinate systems (Figure 1). Each system is described within an XML file<fnref n="4" /> following the ISO 1911 standard. The URI scheme is defined as follows: http://registre.ign.fr/[authority]/[registry]/([version])?/[type_of_resource]/([parent_identifier])*/[resource_identifier]. For example: http://registre.ign.fr/ign/IGNF/crs/RGF93EQGPFR.

<footnote n="1">¹ EURECOM, Sophia Antipolis, France,
<raphael.troncy@eurecom.fr></footnote>

<footnote n="2">² COGIT-IGN, Paris, France, <nathalie-f.abadie@ign.fr></footnote>

<footnote n="3">³ http://www.epsg-registry.org/</footnote>

<footnote n="4">⁴ http://librairies.ign.fr/geoportail/resources/IGNF.xml</footnote>
We have developed a complete vocabulary for defining CRS. We will use the prefix ignf to refer to this vocabulary which is available at http://data.ign.fr/ontologies/ignf#<fnref n="5" />.

<table><caption>Fig. 1. Coordinate Reference System used in France. Source: http://geodesie.ign.fr/</caption><thead><tr><th>REGION</th><th>COORDINATE SYSTEM</th><th>ELLIPSOID</th><th>PROJECTION SYSTEM</th><th>ALTIMETRY SYSTEM</th></tr></thead><tbody><tr><td>FRANCE METROPOLITAN</td><td>RGF93</td><td>IAG GRS 1980</td><td>Lambert 93 and CC 9 Zones</td><td></td></tr><tr><td>MAYOTTE</td><td>RGM04 (ITRF2000)</td><td>IAG GRS 1980</td><td>UTM 38 South</td><td>SHOM 1953</td></tr><tr><td>GUYANE</td><td>RGFG95</td><td>IAG-GRS 1980</td><td>UTM 21 22 North</td><td></td></tr><tr><td>MARTINIQUE</td><td>WGS84</td><td>IAG-GRS 1980</td><td>UTM 20 North</td><td></td></tr><tr><td>GADELOUPE</td><td>WGS84</td><td>IAG-GRS 1980</td><td>UTM 20 North</td><td></td></tr><tr><td>LA RÉUNION</td><td>RGR92</td><td>IAG-GRS 1980</td><td>UTM 40 South</td><td>GGR 99</td></tr><tr><td>NOUVELLE-CALÉDONIE</td><td>ITRF90</td><td>IAG-GRS 1980</td><td></td><td></td></tr><tr><td>POLYNÉSIE</td><td>RGPF</td><td>IAG-GRS 1980</td><td>UTM 5, 6, 7 and 8 South</td><td>Tahiti IGN 1966</td></tr><tr><td>WALLIS ET FUTUNA</td><td>MOP87</td><td>International 1924</td><td></td><td></td></tr><tr><td>SAINT-PIERRE ET MIQUELON</td><td>RGM01 (ITRF2000)</td><td>IAG GRS 1980</td><td>UTM 21 North</td><td>Danger 1950</td></tr><tr><td>ILE CLIPPERTON</td><td>Marine 1967</td><td>International</td><td>UTM 12 South</td><td></td></tr></tbody></table>

## 2 A Vocabulary for Geometries

We have already surveyed in [1] numerous vocabularies for representing geographical features and their geometries, either using a literal à la WKT or a structured representation à la NeoGeo. We have developed a new vocabulary that re-uses and extends the existing vocabularies for representing geometries, namely:

- http://www.opengis.net/ont/geosparql# (prefix gsp<fnref n="6" />. This vocabulary provides the basic concepts to represent geographical data such as SpatialObject, Feature or Geometry. A Feature is linked to a Geometry via the relation gap:hasGeometry. The geometries are strings typed as gmlLiteral or

<footnote n="5">⁵ The vocabulary is temporary available at http://www.eurecom.fr/~atemezin/datalift/ign-onto/ignfV2.pdf</footnote>

<footnote n="6">⁶ All prefixes used in this paper are in line with the prefixes recommended by the Linked Open Vocabulary (LOV) initiative</footnote>
wktLiteral, corresponding respectively to the properties asGML and asWKT.
The vocabulary contains also spatial functions.

- http://www.opengis.net/ont/sf# (prefix sf): This vocabulary describes the standard Simple Features for SQL of OGC. The class sf:Geometry is a subclass of gsp:Geometry.

The extensions are the following:

- Links between geometries and instances of different type

- the representation of geometries in a more structured way

- the integration of coordinate reference systems

We will use the prefix `geom` to refer to the vocabulary we propose available at http://data.ign.fr/ontologies/geom#<fnref n="7" />. In the GeoSPARQL standard, the property `gsp:hasGeometry` links a resource of type `gsp:Feature` to a resource of type `gsp:Geometry`. In our case, we left the domain empty to accept any type of resource links to a geometry. We use the property `geom:geometry` to link a resource to a given Geometry.

The naming convention used for the `geom` vocabulary follows the terms used by the SimpleFeatures vocabulary, the glossary of multilingual terminology of ISO/TC 211, available at http://www.isotc211.org/Terminology.htm.

**Axiom 1** A resource of type `geom:Geometry` should be associated to only one resource of type `ignf:CoordinatesSystem` via the property `geom:crs`.

Alignments: `geom:Geometry` is a subclass of both `sf:Geometry` and `ngeo:Geometry`. It contains in addition the property `geom:crs`.

**Axiom 2** A POINT is a subclass of a GEOMETRY.

**Axiom 3** The instances of the class `geom:Point` are associated with the instance of only one `ignf:CoordinatesSystem` via the property `geom:crs`. An instance of a Point has only one coordinate X and coordinate Y. The coordinates are `xsd:double` and use respectively the following properties:

- `geom:coordX` which refers to, in a particular CRS, the longitude of a point and within a projection coordinate system (CS), the value of false easting of a point.

- `geom:coordY` which refers to, in a particular CRS, the latitude of a point and within a projection CS, the value of false northing point.

On the current usage of positioning on the web of data, it is assumed that the coordinates should be in WGS84, and hence the definition of the point. However, publishers might have data in different CRS according to the location. Thus, our proposal is to define a more generic class for a point with the benefit of choosing the CRS of the underlying data.

<footnote n="7">⁷ The vocabulary is temporary available at http://www.eurecom.fr/~atemezin/datalift/ign-onto/GeometryV8.ttl</footnote>
```json
geom: Point a: owl: Class;
rdfs: label "Point" @en, "Point" @fr;
rdfs: subClassOf geom: Geometry;
owl: equivalentClass
[a owl: Class ;
   owl: intersectionOf
      ([a owl: Restriction;
         owl: onDataRange xsd: double;
         owl: onProperty geom: coordY;
         owl: qualifiedCardinality "1"^^xsd: nonNegativeInteger])
      [a owl: Restriction;
         owl: onDataRange xsd: double;
         owl: onProperty geom: coordX;
         owl: qualifiedCardinality "1"^^xsd: nonNegativeInteger])
   ] ;
rdfs: subClassOf sf: Point.
```

<caption>**Listing 1.1.** Definition in Turtle of the axiom defining a POINT.</caption>

## 3 A REST Service for Converting Geo Data

As we have seen, geo data interpretation relies on a coordinate system, and while the WGS84 standard is the de-facto standard for GPS devices, many other co-ordinates systems are in use. For example LAMBERT 93, RGM 04 or RGR 92 are respectively used to locate points of interests in France continental, Mayotte or La Reunion. We have developed a REST service that is capable of transforming one dataset using a particular coordinates system into another one. The algorithms implemented are the ones described at http://geodesie.ign.fr/index.php?page=algorithms and available within the standalone Circé software<fnref n="8" />. The REST service is available at https://github.com/vienlam/Geo.

## Acknowledgments

This work has been partially supported by the French National Research Agency (ANR) within the Datalift Project, under grant number ANR-10-CORD-009.

## References

1. G. Atemezing and R. Troncy. Comparing Vocabularies for Representing Geographical Features and Their Geometry. In *Terra Cognita Workshop*, 2012.

2. S. Auer, J. Lehmann, and S. Hellmann. LinkedGeoData - Adding a Spatial Dimension to the Web of Data. In *International Semantic Web Conference (ISWC'09)*, 2009.

3. A. de León, L. M. Vilches, B. Villazón-Terrazas, F. Priyatna, and O. Corcho. Geographical linked data: a Spanish use case. In *International Conference on Semantic Systems (I-SEMANTICS'10)*, Graz, Austria, 2010.

<footnote n="8">⁸ http://fr.wikipedia.org/wiki/Circ_(logiciel)</footnote>
4. J. Goodwin, C. Dolbear, and G. Hart. Geographical Linked Data: The Administrative Geography of Great Britain on the Semantic Web. *Transactions in GIS*, 12:19–30, 2008.

5. K. Janowicz, S. Schade, A. Bröring, C. Kessler, C. Stasch, P. Maué, and T. Diekhof. A transparent semantic enablement layer for the geospatial web. In *Terra Cognita Workshop*, 2009.

6. M. Perry and J. Herring. OGC GeoSPARQL- A Geographic Query Language for RDF Data. In *OGC Implementation Standard, ref: OGC 11-052r4*, 2012.

7. J. Salas and A. Harth. Finding spatial equivalences accross multiple RDF datasets. In *Terra Cognita Workshop*, pages 114–126, Bonn, Germany, 2011.