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# `cdshealpix-rust`
**[CDS](http://cdsweb.u-strasbg.fr) implementation of the HEALPix tesselation in Rust and modules to generate libraries in WebAssembly, Python, ...**
[](https://crates.io/crates/cdshealpix)
[](https://crates.io/crates/cdshealpix)
[](https://docs.rs/cdshealpix/)
About
-----
This library is an implementation in Rust of the HEALPix tesselation.
This implementation has been made by the Strasbourg astronomical Data Centre (*Centre de Données astronomique de Strasbourg*, [CDS](http://cdsweb.u-strasbg.fr)).
Initially, it is a port of a part of the CDS Java library available [here](https://github.com/cds-astro/cds-healpix-java),
but improvement have been added while porting the code.
For informations on HEALPix in general, see:
* The [official web site](https://healpix.jpl.nasa.gov/)
* The [Wikipedia page](https://en.wikipedia.org/wiki/HEALPix)
* The two main reference papers: [Gorski (2005)](http://adsabs.harvard.edu/abs/2005ApJ...622..759G) and [Calabretta (2007)](http://adsabs.harvard.edu/abs/2007MNRAS.381..865C)
Official implementations, are available [here](https://healpix.sourceforge.io/). It contains GPL v2 codes in Fortran, C++, Java, IDL, Python, ...
Other independant HEALPix implementations:
* [Astropy-healpix](https://github.com/astropy/astropy-healpix) python wrapper using a C code (C code by Dustin Lang, python wrapper by Thomas Robitaille and others)
* [Javascript/Typescript](https://github.com/michitaro/healpix) implementation by Koike Michitaro
* [Julia](https://github.com/ziotom78/Healpix.jl) implementation by Maurizio Tomasi
* [C](https://sourceforge.net/projects/healpix/files/healpix_bare_1.0/) "official" core functionalities implementation in BSD by Martin Reinecke
* ... (Help me to add links to other HEALPix resources and codes).
Warning
-------
Although the main part of the code uses standard Rust, the nightly version of the compiler is needed to run benches.
So you need to install and compile with Rust nightly:
```bash
# Install the nightly
rustup install nightly
# Either set the default to nightly
rustup default nightly
# Or compile explicitly with nightly
cargo build +nightly
```
Features
--------
* Supports the **HEALix Nested scheme**
+ Supports approximated `cone` and `elliptical cone` and **exact** `polygon` queries
+ Supports `BMOC` (MOC with a flag telling if a cell is fully or partially covered by a surface) as a result of `cone` and `polygon` queries
+ Supports logical operations on `BMOCs` and `BMOC` creation from a list of cell number at a given depth
* Supports the **HEALPix Nested scheme** with **any** NSIDE (i.e. not necessarilly powers of 2)
Missing Features
----------------
* Not supported
* Polygon and ellipse in the RING scheme
* Spherical Harmonics computations
* (Help me fill this)
* Not yet implemented
* Exact cone and ellipse solution (but using the `custom` approx methods, one can handle the rate of false positives)
* Cone query in the RING scheme
Examples
--------
Compute the cell number of a given position on the unit-sphere at a given HEALPix depth.
```rust
use cdshealpix::{nside};
use cdshealpix::nested::{get_or_create, Layer};
let depth = 12_u8;
let lon = 12.5_f64.to_radians();
let lat = 89.99999_f64.to_radians();
let nested_d12 = get_or_create(depth);
let nside = nside(depth) as u_64;
let expected_cell_number = nside * nside - 1
assert_eq!(expected_cell_number, nested_d12.hash(lon, lat));
```
Get the spherical coorinates of the 4 vertices of a given cell at a given depth:
```rust
use cdshealpix::nested::{get_or_create, Layer};
let depth = 12_u8;
let cell_number= 10_u64;
let nested_d12 = get_or_create(depth);
let [
(lon_south, lat_south),
(lon_east, lat_east),
(lon_north, lat_north),
(lon_west, lat_west)
] = nested_d12.vertices(cell_number);
```
Get a hierarchical view (a [MOC](http://www.ivoa.net/documents/MOC/)) on the cells overlapped by a given cone:
```rust
use cdshealpix::nested::{get_or_create, Layer};
let depth = 6_u8;
let nested_d6 = get_or_create(depth);
let lon = 13.158329_f64.to_radians();
let lat = -72.80028_f64.to_radians();
let radius = 5.64323_f64.to_radians();
let moc = nested_d6.cone_overlap_approx(lon, lat, radius);
for cell in moc.into_iter() {
println!("cell: {:?}", cell);
}
```
Standalone
----------
(Not on crates.io, but on github)
The code source of the very beginning of a standalone exec can be found in `cli/src/bin.rs`.
WebAssembly
-----------
(Not on crates.io, but on github)
To build and use the WebAssembly (and Javascript) files, the `libwasmbingen` directory.
We rely on [wasm-bingen](https://github.com/rustwasm/wasm-bindgen).
Python
------
(Not on crates.io, but on github)
See the `libpython` directory containing a very first integration in python using [CFFI](https://cffi.readthedocs.io/en/latest/).
For a clean Python wrapper and associated Wheels, see Matthieu Baumann's project [cds-healpix-python](https://github.com/cds-astro/cds-healpix-python/).
To use the library in python, install it through `pip` (examples are provided on github [cds-healpix-python](https://github.com/cds-astro/cds-healpix-python/)):
```bash
pip install cdshealpix
```
License
-------
Like most projects in Rust, this project is licensed under either of
* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or
http://opensource.org/licenses/MIT)
at your option.
Contribution
------------
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in this project by you, as defined in the Apache-2.0 license,
shall be dual licensed as above, without any additional terms or conditions.
Disclaimer
----------
It a first code in Rust, feel free to give some advice/feedback.