contour 0.5.0

Compute isorings and contour polygons (using marching squares algorithm).
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# contour-rs

[![Build Status Travis](https://travis-ci.org/mthh/contour-rs.svg?branch=master)](https://travis-ci.org/mthh/contour-rs)
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Computes *isorings* and __*contour polygons*__ by applying [marching squares](https://en.wikipedia.org/wiki/Marching_squares) to a rectangular array of numeric values.  
Outputs ring coordinates or polygons contours as a `Vec` of [GeoJSON](https://github.com/georust/rust-geojson) [Feature](https://docs.rs/geojson/0.13.0/geojson/struct.Feature.html)s.  
*Note : This is a port of [d3-contour](https://github.com/d3/d3-contour).*  

<div style="text-align:center"><a href="https://mthh.github.io/wasm_demo_contour/"><img src ="https://raw.githubusercontent.com/mthh/contour-rs/master/illustration.png" /></a></div><br>

### Usage

Add this to your `Cargo.toml`:

```toml
[dependencies]
contour = "0.4.0"
```

and this to your crate root:

```rust
extern crate contour;
```

The API exposes:
- a `contour_rings` function, which computes isorings coordinates for one threshold value (*returns a `Vec` of rings coordinates*).
- a `ContourBuilder` struct, which computes isorings coordinates for a `Vec` of threshold values and transform them in `MultiPolygon`s (*returns a `Vec` of GeoJSON Features*).


### Example:

```rust
let c = ContourBuilder::new(10, 10, false); // x dim., y dim., smoothing
let res = c.contours(&vec![
    0., 0., 0., 0., 0., 0., 0., 0., 0., 0.,
    0., 0., 0., 0., 0., 0., 0., 0., 0., 0.,
    0., 0., 0., 0., 0., 0., 0., 0., 0., 0.,
    0., 0., 0., 1., 1., 1., 0., 0., 0., 0.,
    0., 0., 0., 1., 1., 1., 0., 0., 0., 0.,
    0., 0., 0., 1., 1., 1., 0., 0., 0., 0.,
    0., 0., 0., 1., 1., 1., 0., 0., 0., 0.,
    0., 0., 0., 1., 1., 1., 0., 0., 0., 0.,
    0., 0., 0., 0., 0., 0., 0., 0., 0., 0.,
    0., 0., 0., 0., 0., 0., 0., 0., 0., 0.
], &[0.5])?; // values, thresholds
```
__*Output:*__
```rust
[Feature {
  bbox: None,
  geometry: Some(Geometry {
    bbox: None,
    value: MultiPolygon([[[
      [6., 7.5], [6., 6.5], [6., 5.5], [6., 4.5],
      [6., 3.5], [5.5, 3.], [4.5, 3.], [3.5, 3.],
      [3., 3.5], [3., 4.5], [3., 5.5], [3., 6.5],
      [3., 7.5], [3.5, 8.], [4.5, 8.], [5.5, 8.],
      [6., 7.5]]]]),
    foreign_members: None
    }),
   id: None,
   properties: Some({"value": Number(0.5)}),
   foreign_members: None
   }]
```

### Demo

Demo of this crate compiled to WebAssembly and used from JavaScript : [wasm_demo_contour](https://mthh.github.io/wasm_demo_contour/).

## License

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 the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any
additional terms or conditions.