PROJ in the Browser

Loading WASM module...

A browser-based interface to PROJ, powered by clj-proj. Web interface based on wasm-proj by Javier Jimenez Shaw.

Also targets Node.js and JVM (native FFI via dtype-next, GraalWasm fallback).

How it works

PROJ runs directly in your browser using WebAssembly. The entire library, including its CRS database, runs client-side with no server communication required.

Build:

PROJ is compiled to WASM using Emscripten
Clojure source is compiled to ES6 modules using Cherry
PROJ C function bindings are automatically extracted from fndefs.cljc and exported from WASM
Modules are bundled with esbuild

Runtime:

PROJ runs in Web Workers, keeping the main thread responsive
The same WASM binary is used in both modes; with Cross-Origin Isolation (COOP/COEP headers), SharedArrayBuffer enables Emscripten's internal pthreads within each worker; without it, the module runs single-threaded
Each PROJ context is pinned to a specific worker; the pool uses round-robin assignment
The proj.db and proj.ini files are fetched at startup and written to Emscripten's virtual filesystem in each worker
Grid shift files (NADCON, NTv2, etc.) are fetched on demand from cdn.proj.org when a transformation requires them
C-allocated objects are cleaned up using resource-tracker

Source CRS

Epoch:

Input Coordinates

Target CRS

Epoch:

Decimal Places Output Coordinates

Promote to 3D Use Network

Operation Summary