# H3: A Hexagonal Hierarchical Geospatial Indexing System

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H3 is a geospatial indexing system using a hexagonal grid that can be (approximately) subdivided into finer and finer hexagonal grids, combining the benefits of a hexagonal grid with [S2](https://code.google.com/archive/p/s2-geometry-library/)'s hierarchical subdivisions.

Documentation is available at [https://uber.github.io/h3/](https://uber.github.io/h3/). Developer documentation in Markdown format is available under the [dev-docs](./dev-docs/) directory.

 * Post **bug reports or feature requests** to the [GitHub Issues page](https://github.com/uber/h3/issues)
 * Ask **questions** by posting to the [H3 tag on StackOverflow](https://stackoverflow.com/questions/tagged/h3)

## Installing

We recommend using prebuilt bindings if they are available for your programming language. Bindings for [Go](https://github.com/uber/h3-go), [Java](https://github.com/uber/h3-java), [JavaScript](https://github.com/uber/h3-js), [Python](https://github.com/uber/h3-py), and [others](https://uber.github.io/h3/#/documentation/community/bindings) are available.

On macOS, you can install H3 using brew:
```
brew install h3
```
Otherwise, to build H3 from source, please see the following instructions.

### Building from source

Still here? To build the H3 C library, you'll need a C compiler (tested with `gcc` and `clang`), [CMake](https://cmake.org/), and [Make](https://www.gnu.org/software/make/). If you intend to contribute to H3, you must have [clang-format](https://clang.llvm.org/docs/ClangFormat.html) installed and we recommend installing [ccmake](https://cmake.org/cmake/help/v3.0/manual/ccmake.1.html) and [LCOV](http://ltp.sourceforge.net/coverage/lcov.php) to configure the `cmake` arguments to build and run the tests and generate the code coverage report. We also recommend using `gcc` for the code coverage as some versions of `clang` generate annotations that aren't compatible with `lcov`. [Doxygen](http://www.stack.nl/~dimitri/doxygen/) is needed to build the API documentation.

#### Install build-time dependencies

* Alpine 
```
# Installing the bare build requirements
apk add cmake make gcc libtool musl-dev
```

* Debian/Ubuntu

```
# Installing the bare build requirements
sudo apt install cmake make gcc libtool
# Installing useful tools for development
sudo apt install clang-format cmake-curses-gui lcov doxygen
```

* macOS (using brew)

First make sure you [have the developer tools installed](http://osxdaily.com/2014/02/12/install-command-line-tools-mac-os-x/) and then

```
# Installing the bare build requirements
brew install cmake
# Installing useful tools for development
brew install clang-format lcov doxygen
```

* Windows (Visual Studio)

You will need to install CMake and Visual Studio, including the Visual C++ compiler. For building on Windows, please follow the [Windows build instructions](dev-docs/build_windows.md).

#### Compilation

From the repository you would then compile like so:

```
cmake .
make
```

You can install system-wide with:

```
sudo make install
```

#### Testing

After making the project, you can test with `make test`, and if `lcov` is installed you can `make coverage` to generate a code coverage report.

#### Documentation

You can build developer documentation with `make docs` if Doxygen was installed when CMake was run. Index of the documentation will be `dev-docs/_build/html/index.html`.

After making the project, you can build KML files to visualize the hexagon grid with `make kml`. The files will be placed in `KML`.

To build the documentation website, see the [website/](./website/) directory.

## Usage

### From the command line

To get the H3 index for some location:

```
./bin/geoToH3 10
40.689167 -74.044444
```

10 is the H3 resolution, between 0 (coarsest) and 15 (finest). The coordinates entered are the latitude and longitude, in degrees, you want the index for (these coordinates are the Statue of Liberty).  You should get an H3 index as output, like `8a2a1072b59ffff`.

You can then take this index and get some information about it, for example:

```
./bin/h3ToGeoBoundary
8a2a1072b59ffff
```

This will produce the vertices of the hexagon at this location:

```
8a2a1072b59ffff
{
   40.690058601 -74.044151762
   40.689907695 -74.045061792
   40.689270936 -74.045341418
   40.688785091 -74.044711031
   40.688935993 -74.043801021
   40.689572744 -74.043521377
}
```

You can get the center coordinate of the hexagon like so:

```
./bin/h3ToGeo
8a2a1072b59ffff
```

This will produce some coordinate:

```
40.6894218437 -74.0444313999
```

### From C

The above features of H3 can also be used from C. For example, you can compile and run [examples/index.c](./examples/index.c) like so:

```
cc -lh3 examples/index.c -o example
./example
```

You should get output like:

```
The index is: 8a2a1072b59ffff
Boundary vertex #0: 40.690059, -74.044152
Boundary vertex #1: 40.689908, -74.045062
Boundary vertex #2: 40.689271, -74.045341
Boundary vertex #3: 40.688785, -74.044711
Boundary vertex #4: 40.688936, -74.043801
Boundary vertex #5: 40.689573, -74.043521
Center coordinates: 40.689422, -74.044431
```

## Contributing

Pull requests and Github issues are welcome. Please see our [contributing guide](./CONTRIBUTING.md) for more information.

Before we can merge your changes, you must agree to the [Uber Contributor License Agreement](https://cla-assistant.io/uber/h3).

## Legal and Licensing

H3 is licensed under the [Apache 2.0 License](./LICENSE).

DGGRID
Copyright (c) 2015 Southern Oregon University