# erlang-h3
[](https://github.com/helium/erlang-h3/actions/workflows/ci.yml)
[](https://hex.pm/packages/h3)
The `erlang-h3` library provides an Erlang binding for [Uber's
H3](https://uber.github.io/h3) spatial coordinate library.
Install
------
Add `h3` to your `deps` section in `rebar.config`:
``` shell
{deps, [h3]}.
```
Building
--------
Fork the repo and simply use `make` to build the library. You will
need `cmake` installed to build the required h3 core package.
To run the tests run `make test`.
## Cross compilation
Cross-compilation requires the environment variable `ERTS_INCLUDE_DIR`
defined as the target directory containing `erl_nif.h`,
e.g. `ERTS_INCLUDE_DIR=target/usr/lib/erlang/erts-<VERSION>/include`.
Usage
-----
The `h3` module exports most of the functions from the core H3 library.
Like the JavaScript version the Erlang binding uses degrees instead of
radians when converting to and from geo-coordinates to h3 indexes.
Example using `./rebar3 shell` after cloning the repo:
```shell
$ ./rebar3 shell
...
1> Paris = h3:from_geo({48.8566, 2.3522}, 9).
617550903642685439
2> h3:to_string(Paris).
"891fb466257ffff"
3> h3:to_geo(Paris).
{48.857078058197295,2.3529900909549206}
```
