proj-rust

Pure-Rust coordinate transformation library. No C libraries, no build scripts, no unsafe code.

This workspace currently contains:

• proj-core: transform engine, CRS registry, projection math, and datum shifts
• proj-wkt: parsing and compatibility helpers for EPSG codes, WKT, PROJ strings, and PROJJSON

Release Scope

proj-rust is intended for production use within its supported CRS and projection set. It is not a full implementation of all PROJ capabilities.

Current non-goals for the 0.2 release line include:

• grid-shift based datum transforms
• vertical or time-dependent CRS operations
• full PROJ pipeline semantics and operation selection by area of use
• complete axis-order coverage and full arbitrary angular/unit-model coverage across all CRS definitions

Usage

use proj_core::{Bounds, Transform};

// WGS84 geographic (degrees) -> Web Mercator (meters)
let t = Transform::new("EPSG:4326", "EPSG:3857").unwrap();
let (x, y) = t.convert((-74.006, 40.7128)).unwrap();

// Inverse: Web Mercator -> WGS84
let inv = t.inverse().unwrap();
let (lon, lat) = inv.convert((x, y)).unwrap();

// Works with geo_types::Coord<f64> (with `geo-types` feature)
let coord = geo_types::Coord { x: -74.006, y: 40.7128 };
let projected: geo_types::Coord<f64> = t.convert(coord).unwrap();

// Batch transforms
let coords: Vec<(f64, f64)> = vec![(-74.006, 40.7128); 1000];
let results = t.convert_batch(&coords).unwrap();

// 3D transforms preserve the third ordinate unchanged
let (x, y, h) = t.convert_3d((-74.006, 40.7128, 15.0)).unwrap();
assert_eq!(h, 15.0);

// Reproject an extent by densifying its perimeter
let bounds = Bounds::new(-74.3, 40.45, -73.65, 40.95);
let projected_bounds = t.transform_bounds(bounds, 8).unwrap();
assert!(projected_bounds.max_x > projected_bounds.min_x);

Coordinates use the CRS's native units: degrees for geographic CRS, and the CRS's declared linear unit for projected CRS (for example meters or US survey feet). For convert_3d(), the z component is preserved unchanged because the current CRS model is horizontal-only.

Supported Input Formats

With proj-core, transforms can be created from registry-backed EPSG codes such as "EPSG:4326" and "EPSG:3857".

With proj-wkt, the following CRS definition formats are supported:

• EPSG authority codes and bare EPSG numbers
• OGC CRS:84 aliases and EPSG URNs
• common PROJ strings for the implemented projection families, including legacy +init=epsg:XXXX
• WKT1 and the supported WKT2 projected/geographic CRS forms, including top-level EPSG ID[...]
• basic PROJJSON geographic and projected CRS definitions for the implemented methods

Custom WKT, PROJJSON, and PROJ string definitions are only accepted when they map cleanly onto this workspace's native CRS model: 2D longitude/latitude geographic coordinates in degrees with a Greenwich prime meridian, and projected coordinates in native linear units with easting/northing axis order. Definitions that require unsupported axis-order, prime-meridian, or geographic angular-unit semantics are rejected instead of being silently degraded.

Supported CRS

Custom CRS definitions can be constructed and passed to Transform::from_crs_defs(). The companion proj-wkt crate parses EPSG codes, a subset of WKT/PROJ strings, and basic PROJJSON inputs into CrsDef values.

Compatibility Surface

proj-wkt also exposes a lightweight Proj compatibility facade for downstream code that currently uses the common new_known_crs / new / create_crs_to_crs_from_pj / convert flow. It is intentionally narrow and only covers the supported CRS semantics in this workspace.

proj-core::Transform and proj-wkt::Proj also expose inverse-transform construction and sampled bounds reprojection via inverse() and transform_bounds().

Feature Flags

Testing

cargo test                        # all tests
cargo test -p proj-core --no-default-features  # core crate without rayon/geo-types
./scripts/run-reference-parity.sh
./scripts/verify-release-packaging.sh
cargo clippy --all-targets -- -D warnings

Prefer convert_batch() for small and medium batch sizes. convert_batch_parallel() uses Rayon for larger batches and falls back to the sequential path when that is likely to be faster.

For reference comparisons and current benchmark results against bundled C PROJ, see docs/benchmark-report.md.

Publishing

Release this workspace as a 0.x line with scoped claims: production-ready for the supported projection families and CRS formats above, but not a claim of full PROJ parity.

Publish order matters because proj-wkt depends on proj-core as a separately published crate:

./scripts/verify-release-packaging.sh
cargo publish -p proj-core

# wait for crates.io to index the new proj-core version

cargo package -p proj-wkt --allow-dirty
cargo publish -p proj-wkt

proj-core packages and verifies independently. proj-wkt will not package for upload until the matching proj-core version is available in the crates.io index.

License

MIT OR Apache-2.0