Crs

Crs

use qgis_render::crs::*;

A coordinate reference system: how coordinates map onto the earth. Every Project, Layer, and render has one, and mismatches between them are resolved by transforming.

Construction

let wgs84 = Crs::from_epsg(4326)?;         // WGS 84, geographic
let mercator = Crs::from_epsg(3857)?;      // Web Mercator, projected
let utm34 = Crs::from_proj4("+proj=utm +zone=34 +datum=WGS84")?;
let custom = Crs::from_wkt("GEOGCS[\"WGS 84\", ...]")?;

All constructors return Result<Crs, QgisError> and fail with QgisError::CrsError when PROJ cannot resolve the definition.

Properties

Method	Returns
is_geographic()	bool — lat/lon units
is_projected()	bool — metre units
epsg()	Option<u32>
to_wkt()	String
to_proj4()	String

Transforming coordinates

let transform = CoordTransform::new(&Crs::from_epsg(4326)?, &Crs::from_epsg(3857)?)?;

let (x, y) = transform.transform(14.0, 50.0)?;      // lon/lat → metres
let batch = transform.transform_batch(&[(14.0, 50.0), (15.0, 51.0)])?;

Build a CoordTransform once and reuse it — constructing one resolves a PROJ pipeline, which is far more expensive than a single transform call.

Transforming geometries

let reprojected = geom.transform(&wgs84, &mercator)?;

Common choices

EPSG	Name	Typical use
4326	WGS 84	Data exchange, GeoJSON, WFS output.
3857	Web Mercator	XYZ tiles and web maps.
25832–25835	ETRS89 / UTM	Metric work in Europe.
2180	PL-1992	National grid for Poland.

Note

Render output CRS and project CRS do not have to match — pass the CRS you want to RenderSettings and let the renderer reproject.

See also

• crs module — module-level helpers and CoordTransform
• Geometry — transform on geometries
• QGIS Integration — how QGIS models CRS