Rust library for transforming geographic point coordinates from one coordinate system to another. This is a pure Rust implementation of the PROJ.4 project.

The documentation is available on docs.rs and the demo on docs.3liz.org.

Features and Limitations

• The aim of Proj4rs is to provide the same functionality as the proj4js library.
• This port implements the PROJ.4 API, which means there's no 3D/4D/orthometric transformation ATM.
• The goal of Proj4rs is not to be a replacement of PROJ, but instead being a lightweight implementation of transformations from CRS to CRS that could be used in Rust and WASM environments.
• This crate does not provide support for WKT. Instead, there is a dedicated crate for transforming WKT strings to proj string.
• It aims to be WASM compatible for the wasm32-unknown-unknown target.
• No installation of external C libraries such as libproj or sqlite3 is needed.

Basic usage in Rust

Define the coordinate system with proj strings and use the transform function. You can easily get the projection string of any coordinate system from EPSG.io.

Note: Proj4rs use radians as natural angular unit (as does the original proj library)

Example:

use proj4rs;
use proj4rs::proj::Proj;

// EPSG:5174 - Example
let from = Proj::from_proj_string(concat!(
    "+proj=tmerc +lat_0=38 +lon_0=127.002890277778",
    " +k=1 +x_0=200000 +y_0=500000 +ellps=bessel",
    " +towgs84=-145.907,505.034,685.756,-1.162,2.347,1.592,6.342",
    " +units=m +no_defs +type=crs"
))
.unwrap();

// EPSG:4326 - WGS84, known to us as basic longitude and latitude.
let to = Proj::from_proj_string(concat!(
    "+proj=longlat +ellps=WGS84",
    " +datum=WGS84 +no_defs"
))
.unwrap();

let mut point_3d = (198236.3200000003, 453407.8560000006, 0.0);
proj4rs::transform::transform(&from, &to, &mut point_3d).unwrap();

// Note that WGS84 output from this library is in radians, not degrees.
point_3d.0 = point_3d.0.to_degrees();
point_3d.1 = point_3d.1.to_degrees();

// Output in longitude, latitude, and height.
println!("{} {}",point_3d.0, point_3d.1); // 126.98069676435814, 37.58308534678718

WKT support

If you need full support for WKT, please rely on proj which provides a great implementation of the standards.

If you want WKT support in WASM, please have a look at:

• https://github.com/3liz/proj4wkt-rs
• https://github.com/frewsxcv/crs-definitions

Grid shift supports

Nadgrid support is still experimental. Currently, only Ntv2 multi grids are supported for native build and WASM.

JavaScript API

When compiled for WASM, the library exposes JavaScript API that is very similar to that of proj4js. A thin JavaScript layer provides full compatibility with proj4js and thus can be used as a proj4js replacement.

Example:

let from = new Proj.Projection("+proj=latlong +ellps=GRS80");
let to = new Proj.Projection("+proj=etmerc +ellps=GRS80");
let point = new Proj.Point(2.0, 1.0, 0.0);

// Point is transformed in place
Proj.transform(from, to, point);

Compiling for WASM

Install wasm-pack

wasm-pack build --target web --no-default-features

Or if you have installed cargo-make, use the following command:

cargo make wasm

Running the WASM example

There is a index.html file for testing the WASM module in a navigator.

For security reasons, you need to run it from a server. You can start a Python server with the following command:

python3 -m http.server

The server will automatically serve the index.html file in the current directory.

Build for npm

cargo make wasm_bundle

This will create a npm bundler package in pkg-bundler