# rdf-geopackage
[](https://www.npmjs.com/package/@rdmr-eu/rdf-geopackage)
Generate RDF out of a GeoPackage file.
Outputs a Facade-X-like model, supports different CRSs (map projections), limited layers, and many GeoSPARQL features, like GeoJSON, bounding boxes, centroids, WKTs.
[Example RDF dataset](https://triplydb.com/RedmerKronemeijer/rdf-geopackage) and [query results on a map](https://triplydb.com/RedmerKronemeijer/-/queries/rdf-geopackage-PDOK-provinces/1).
## Usage
Install using NPM locally `npm install --global @rdmr-eu/rdf-geopackage` as a command line tool.
Check if it's installed correctly with `rdf-geopackage --help`.
That should return the following help info:
```man
Generate RDF from an OGC GeoPackage with rdf-geopackage
Options:
--help Show help [boolean]
--version Show version number [boolean]
-i, --input GeoPackage file [string]
-o, --output Output quads file [string]
--format Override output format (default: nquads)
[choices: "nq", "nquads", "trig", "nt", "ntriples", "ttl", "turtle"]
--bbox Limit features to bounding box [string]
--bbox-crs Coordinate Reference System code [string]
--only-layers Only output named feature layers and attribute ta
bles [array]
--include-binary-values Output binary values [boolean]
--base-iri Base IRI [string]
--model Data meta model [choices: "facade-x"]
--geosparql Output GeoSPARQL
[array] [choices: "wkt", "geojson", "bbox", "centroid", "length-area"] [defaul
t: ["wkt"]]
```
## Options
Basic input and output serializations can be set with the following options:
- `--input`: the path to the input GeoPackage file (required). With `-`, it reads the GeoPackage from stdin, e.g., piping a file with curl
- `--output`: path to the file output. By default, `rdf-geopackage` outputs _nquads_ to stdout. Its extension sets the serialization format, optionally with `.gz` to GZip the output. E.g., `--output myfile.ttl.gz`
- `--format`: set the output format explicitly. Provide a file extension with `.gz` to GZip the output.
Work with large GeoPackages by limiting the output features, output tables and binary values:
- `--bbox` limits the the output features to those in this area (default CRS: WGS84)
- `--bbox-crs` indicates the CRS for the aforementioned bounding box. Supply a EPSG code (web lookup with EPSG.io) or a projection WKT.
- `--only-layers` limits which feature layers (or attribute tables!) are output.
- `--include-binary-values` overrides the default of skipping binary values. These will be base64 encoded string values with a `^^xsd:base64Binary` data type. NULL values are never output.
Modify the model and types of the output triples or quads:
- `--base-iri`: set the relative base for the output RDF data. By default, this value is derived from the present working directory.
- `--model`: the GeoPackage tables are not natively RDF data, so a module is programmed to generating triples according to a data meta-model. Included modules:
- **default**: [`facade-x`](#model-facade-x)
- `--geosparql`: modify which GeoSPARQL geometries, serializations and properties are output. Only the WKT literal is in layer native CRS, all other are calculated and/or projected.
Multiple values (space separated) are allowed.
Included feature predicates are listed in the table below.
| Option | GeoSPARQL feature predicates | Note |
| ------------------- | ----------------------------------------- | --------------------------------------------------------------- |
| `wkt` (**default**) | `geo:hasGeometry/geo:asWKT` | Output the feature's geometry as a WKT string literal |
| `geojson` | `geo:hasGeometry/geo:asGeoJSON` | Output the feature's geometry as a WGS84 GeoJSON string literal |
| `bbox` | `geo:hasBoundingBox` | Output a feature's bounding box |
| `centroid` | `geo:hasCentroid` | Output a feature's centroid point |
| `length-area` | `geo:hasMetricLength` `geo:hasMetricArea` | Output the length (in m) and area (in m²) of the feature |
| _always on_ | `rdf:type geo:Feature` | Output the feature class |
## RDF output
#### Model: Facade-X
Facade-X is a data meta-model from the SPARQL-Anything project, that can easily represent tabular data.
Facade-X uses RDF containers and blank nodes to represent tables and rows.
Column metadata is currently very limited ([GH-24]) and many values are not typed properly.
[GH-24]: https://github.com/redmer/rdf-geopackage/issues/24
#### Features, geometries and CRS’s
Features and their geometries are represented using [GeoSPARQL][geosparql].
Only rows from feature tables are a `geo:Feature`.
A feature has zero or more geometries predicated with `geo:hasDefaultGeometry`.
There might be no geometry if the underlying library does not support the geometry type.
There may be multiple geometries if the feature is from a layer not in EPSG:4326.
That's because a GeoJSON serialization (`geo:asGeoJSON`) is always (reprojected) in EPSG:4326.
A `geo:Geometry` can be in only one CRS, meaning that when the feature is not originally in EPSG:4326, other serializations should also be reprojected.
That is undesirable, so in these cases, `rdf-geopackage` generates a second `geo:Geometry` for the WKT serialization (`geo:asWKT`).
[geosparql]: https://www.ogc.org/standard/geosparql/
#### Example RDF output
Example data abridged [from NGA][example.gpkg]:
the table `media` is a feature table, `nga_properties` is an attribute table.
[example.gpkg]: https://github.com/ngageoint/GeoPackage/blob/master/docs/examples/java/example.gpkg
```turtle
prefix fx:
prefix geo:
prefix rdf:
prefix xsd:
prefix xyz:
xyz:nga_properties { # representing a table
xyz:nga_properties a fx:root ; # representing a table
rdf:_1 [ # the first row
xyz:id 14;
xyz:property "subject";
xyz:value "Examples"
] .
}
xyz:media {
xyz:media a fx:root ;
rdf:_1 [
a geo:Feature ; # a row from a feature table
xyz:text "BIT Systems";
xyz:date "2023-01-23";
geo:hasDefaultGeometry [ # single geometry as CRS is EPSG:4326
a geo:Geometry ;
geo:asWKT "POINT (-104.801918 39.720014)"^^geo:wktLiteral ;
geo:asGeoJSON "{\"coordinates\":[-104.801918,39.720014],\"type\":\"Point\"}"^^geo:geoJSONLiteral
]
] .
}
```
# Acknowledgements
This tool was developed for a project funded by the [_City Deal Openbare ruimte_][cdor],
executed by [Stichting Kennisplatform CROW][crow].
[crow]: https://crow.nl/
[cdor]: https://www.citydealopenbareruimte.nl/