proj9-js

proj9-js

Experimental JavaScript/TypeScript port inspired by PROJ 9 semantics.

$3

- v0.1.1:
- EPSG:4326 ↔ EPSG:3857 transforms using a pipeline/step architecture
- transformMany() + EPSG aliases + 3D coord support
- EGM96 vertical conversion (ellipsoidal ↔ orthometric) with bundled data/egm96_15.gtx
- Bundles data/proj.db and exposes stable APIs to locate it (DB not used yet)

$3

``bash
npm i proj9-js
`

$3

`ts
import { createTransformer, getBundledProjDbPath, transform, transformMany } from "proj9-js";
import { setProjDataDir } from "proj9-js";

const xy = transform("EPSG:4326", "EPSG:3857", [180, 0]);
const ll = transform("EPSG:3857", "EPSG:4326", xy);

const t = createTransformer("EPSG:4326", "EPSG:3857");
const xy2 = t.forward([12, 34]);

// Batch transform (build once, apply many)
const batch = transformMany("EPSG:4326", "EPSG:3857", [
[0, 0],
[1, 2],
[180, 0],
]);

// EPSG aliases are accepted:
// - "4326" / "3857"
// - "epsg:4326"
// - "EPSG::4326"
// - "urn:ogc:def:crs:EPSG::4326"
// - "CRS:84"
// - "EPSG:4979"
const xyAlias = transform("4326", "3857", [180, 0]);

// 3D coords are accepted.
// For most ops today, z is passed through unchanged.
const xyz = transform("CRS:84", "EPSG:3857", [12.34, 56.78, 9]);
// => [x, y, 9]

console.log(getBundledProjDbPath());
`

$3

This package can convert ellipsoidal height ↔ EGM96 orthometric height using a geoid grid:

- Ellipsoidal height: EPSG:4979
- EGM96 height: EPSG:4326+EGM96 (shorthand: "EGM96")

proj9-js ships with the EGM96 grid bundled by default (data/egm96_15.gtx).
You can override it via setProjDataDir() (or PROJ_DATA / PROJ_LIB) if you want to use a different PROJ data directory.

`ts
import { setProjDataDir, transform } from "proj9-js";

setProjDataDir("/path/to/proj-data"); // optional override; otherwise bundled data is used

// h -> H (H = h - N)
const H = transform("EPSG:4979", "EPSG:4326+EGM96", [12.34, 56.78, 100]);

// H -> h (h = H + N)
const h = transform("EGM96", "EPSG:4979", H);
`

$3

- EGM96 grid is derived from the official PROJ-data dataset (cdn.proj.org): us_nga_egm96_15.tif.

$3

This package ships a data/proj.db asset and provides:

- getBundledProjDbPath(): string
- getBundledProjDbBuffer(): Buffer
- setProjDataDir(path: string): void

The DB is not read yet (planned for v0.2.0). You can refresh data/proj.db later via npm run download:projdb once you pick a specific PROJ release source.

$3

This repo is intended to follow standard npm package release automation:

- Releases are created from main via GitHub Actions + semantic-release.
- Version bumps and CHANGELOG.md` entries are generated from Conventional Commits.