geometry-io-geojson

Part of the boost_geometry workspace — a Rust port of Boost.Geometry. Most users should depend on the facade crate, which re-exports this one; depend on this crate directly only for a slimmer build.

RFC 7946 GeoJSON reader and writer.

Not part of Boost.Geometry; follows RFC 7946. The parser emits a [geometry_model::DynGeometry] (a GeoJSON GeometryCollection is heterogeneous); the writer serialises concrete model geometries with [to_geojson] and any user-defined polygon implementing the geometry traits with [to_geojson_polygon]. Feature objects and property bags are out of scope — only the geometry member's OGC-equivalent kinds.

Serialize a user-defined polygon

Application types can implement the lightweight [geometry_trait] traits directly; they do not need to be converted to a geometry_model polygon.

use geometry_cs::Cartesian;
use geometry_io_geojson::{from_geojson, to_geojson_polygon};
use geometry_tag::{PointTag, PolygonTag, RingTag};
use geometry_trait::{Geometry, Point, Polygon, Ring};

struct Coordinate(f64, f64);

impl Geometry for Coordinate {
    type Kind = PointTag;
    type Point = Self;
}

impl Point for Coordinate {
    type Scalar = f64;
    type Cs = Cartesian;
    const DIM: usize = 2;

    fn get<const D: usize>(&self) -> f64 {
        match D {
            0 => self.0,
            1 => self.1,
            _ => unreachable!("a Coordinate has two dimensions"),
        }
    }
}

struct Boundary(Vec<Coordinate>);

impl Geometry for Boundary {
    type Kind = RingTag;
    type Point = Coordinate;
}

impl Ring for Boundary {
    fn points(&self) -> impl ExactSizeIterator<Item = &Coordinate> + Clone {
        self.0.iter()
    }
}

struct Parcel {
    exterior: Boundary,
    holes: Vec<Boundary>,
}

impl Geometry for Parcel {
    type Kind = PolygonTag;
    type Point = Coordinate;
}

impl Polygon for Parcel {
    type Ring = Boundary;

    fn exterior(&self) -> &Boundary {
        &self.exterior
    }

    fn interiors(&self) -> impl ExactSizeIterator<Item = &Boundary> {
        self.holes.iter()
    }
}

let parcel = Parcel {
    exterior: Boundary(vec![
        Coordinate(0.0, 0.0),
        Coordinate(0.0, 2.0),
        Coordinate(2.0, 2.0),
        Coordinate(2.0, 0.0),
        Coordinate(0.0, 0.0),
    ]),
    holes: vec![],
};

let geojson = to_geojson_polygon(&parcel);
assert_eq!(
    geojson,
    r#"{"type":"Polygon","coordinates":[[[0,0],[0,2],[2,2],[2,0],[0,0]]]}"#
);
assert!(from_geojson(&geojson).is_ok());

License

BSL-1.0 — see LICENSE.