GeoSPARQL

PurRDF evaluates spatial predicates, geographic metrics, buffers and explicit coordinate operations in process, over the dataset a query already holds. purrdf-geo is the Rust facade: it reexports the geometry and geographic types from purrdf-geo-kernel and the native evaluator’s scalar and property-function adapters. The computational kernel depends on no SPARQL evaluator, GEOS, PROJ or external geographic runtime. The same kernel serves Rust, Python, C, WebAssembly and the CLI.

References are explicit

The standard geographic profile assigns unprefixed WKT, OGC CRS84 and GeoJSON to WGS84 longitude followed by latitude. Original decimal coordinates remain exact rationals. Longitude outside [-180, 180] and latitude outside [-90, 90] refuse before conversion; valid inputs are never wrapped or clamped.

EPSG:4326 requires an explicit WGS84 latitude/longitude registration. Other references, units and operation chains require caller registrations. An ellipsoid does not establish a datum transformation, and the engine does not guess zones, height, epoch, control points or regional transformation parameters. Standard OGC terms have their published meanings; application namespaces and custom registrations remain caller supplied.

Geographic profiles and requests specifies the versioned JSON records, reference axes, operation parameters, limits, identity rules and every host entry.

Scalar functions in the native query engine

The default NativeSparqlEngine installs the immutable standard geof: functions. Registering a conflicting standard function is a hard error before execution. A query selects additional bindings and independent numerical limits with QueryOptions::with_geo:

use purrdf::geo::GeoProfile;
use purrdf::sparql::{NativeSparqlEngine, QueryOptions};
use purrdf::SparqlRequest;

let profile = GeoProfile::standard();
let result = NativeSparqlEngine::new().query_with_options_view(
    &dataset,
    SparqlRequest {
        query: r#"PREFIX geof: <http://www.opengis.net/def/function/geosparql/>
                  PREFIX geo: <http://www.opengis.net/ont/geosparql#>
                  SELECT (geof:metricDistance(
                    "POINT(0 0)"^^geo:wktLiteral,
                    "POINT(1 0)"^^geo:wktLiteral) AS ?metres)
                  WHERE {}"#,
        base_iri: None,
        substitutions: &[],
    },
    QueryOptions::new().with_geo(&profile),
)?;

Geographic metricDistance, metricLength, metricPerimeter, metricArea and metricBuffer, and their explicit-unit counterparts, use the declared ellipsoid. Projected metre systems retain their planar law. Length includes polygon boundaries and preserves the declared mixed-dimension rule; area subtracts holes and squares unit factors. Z and M are retained without inventing an elevation.

Malformed arguments and geometric domain errors retain SPARQL expression-error behavior. Operational precision, work, memory, convergence, cancellation and floating-environment failures remain fatal through FILTER and BIND. Governed evaluation retains its original incomplete-outcome and work evidence. The direct geographic request API preserves the same typed causes instead of turning a refused invocation into an empty result.

Geometry and geographic laws

WKT and GeoJSON retain their original coordinate-linear edges, including a written long route across longitude. Explicit shortest-geodesic and azimuth/length arcs retain their selected branches; ambiguous endpoint-only arcs refuse. Prepared regions represent holes, complements and the whole surface. Metrics, topology, continuous coordinate-operation images, buffers and covers use those same prepared curves and regions.

Point distance is the correctly rounded shortest ellipsoidal distance at six decimal metre places, using half-even rounding. A complete certified enclosure must select one rounded answer; acceptable approximation error alone does not authorize a result. Direct coordinates use the declared angular grid. Geometric distance, length, perimeter, area and outward buffers carry their own declared certificates and rounding laws. The numerical primitives have one home in purrdf-xsd; no platform libm or reassociated reduction selects an answer.

Explicit coordinate chains cover projections, geographic/geocentric conversion, the named GCJ/BD equations, and caller-parameter Helmert, similarity, polynomial and in-memory grid models. Bounded inverses isolate all admissible roots and refuse ambiguity. These mathematical laws do not claim surveying accuracy or official provider certification.

Spatial relations and cells

The property-function adapter projects caller-selected geometry predicates into a reusable GeoIndex and registers the selected Simple Features, Egenhofer or RCC8 relations. Asserted relation triples retain their RDF meaning; calculated relations add the entailed matches. The actual query’s selected geographic context and original allocation owners remain live through the cursor. An empty relation-family registration refuses.

The native cubed-sphere hierarchy assigns profile-qualified cell IDs at levels 0–30. Parent/child operations, big-endian keys and ordered ranges share that definition. Closed disk, box and prepared-region covers are conservative; caller limits refuse a complete cover rather than truncate or silently coarsen it. Reusable point indexes keep original coordinates and refine candidates with the requested physical or reported-distance law. h3 v4.0 compatibility is an architecture document, not an implemented family.

Host ownership and qualification

GeoSession and GeoPointIndex expose the same versioned requests on every host. Python query and update entries accept geo=. WebAssembly engines snapshot the selected profile for suspended operations. C provides opaque create/call/free handles and context-taking query entries. The CLI accepts --geo-profile for geographic requests, queries and updates.

A semantic refusal has a complete response record. An operational refusal keeps its original failure channel and creates no unadmitted response under the failed invocation. Prepared data is immutable and shareable; live numerical contexts stay thread bound. Native storage is admitted before birth and retained until its actual payload is destroyed.

Frozen numerical, geometry and hierarchy transcripts compare completed native and WebAssembly answers. The public GeodTest collector checks the complete 500,000-row source by digest, while allocator, backend and host fixtures check their separate contracts. Mathematical derivations and exactness boundaries are recorded in Geodesic numerics and Geometry exactness.