Contour-isobands-rs

Compute isobands (i.e. contour polygons which enclose all the points of a grid included between two given values) by applying marching squares to an array of values.

Usage

Add the following to your Cargo.toml:

toml [dependencies] contour-isobands-rs = "0.2.0"

Then, you can use the ContourBuilder to compute isobands:

```rust use contourisobandsrs::{ContourBuilder, Band};

let values = vec![ 1., 1., 1., 1., 1., 1., 1., 1., 5., 5., 5., 5., 5., 1., 1., 5., 15., 15., 15., 5., 1., 1., 5., 10., 10., 10., 5., 1., 1., 5., 5., 5., 5., 5., 1., 1., 1., 1., 1., 1., 1., 1., ];

// These intervals will compute 3 bands: // - the first one will contain all points between 1 (included) and 5 (excluded) // - the second one will contain all points between 5 (included) and 7 (excluded) // - the third one will contain all points between 7 (included) and 15 (included) let intervals = vec![1, 5, 7, 15];

let result: Vec = ContourBuilder::new(7, 6) .use_quadtree(true) .contours(&values, &intervals)?;

assert_eq!(result.len(), 3); ```

Each Band struct contains a geometry (MultiPolygon<f64>) and the minimum and maximum values of the band. It can be serialized to geojson using the geojson feature:

toml [dependencies] contour-isobands-rs = { "0.2.0", features = ["geojson"] }

```rust use contourisobandsrs::{ContourBuilder, Band}; use geojson::{Feature, FeatureCollection};

let values = vec![ 1., 1., 1., 1., 1., 1., 1., 1., 5., 5., 5., 5., 5., 1., 1., 5., 15., 15., 15., 5., 1., 1., 5., 10., 10., 10., 5., 1., 1., 5., 5., 5., 5., 5., 1., 1., 1., 1., 1., 1., 1., 1., ];

let intervals = vec![1, 5, 7, 15];

let result = ContourBuilder::new(7, 6) .use_quadtree(true) .contours(&values, &intervals)?;

let features = result.iter() .map(|band| band.to_geojson()) .collect::>();

let geojsonstring = GeoJson::from( FeatureCollection { bbox: None, features, foreignmembers: None, }).to_string(); ```

Note that you can specify the coordinates of the grid and the distance between points (on x- and y-axis) using the x_origin, y_origin, x_step and y_step parameters of the ContourBuilder constructor :

rust let result: Vec<Band> = ContourBuilder::new(7, 6) .x_origin(-6.141583932015321) .y_origin(51.7591540368963) .x_step(-0.119) .y_step(0.09) .use_quadtree(true) .contours(&values, &intervals)?;

WASM demo

A demo of this crate, compiled to WebAssembly, is available on https://mthh.github.io/contour-isobands-wasm/.

Difference with the contour crate (from mthh/contour-rs repository)

While the contour crate computes isolines (cf. wikipedia:Marchingsquares) and their corresponding polygons *(i.e. polygons that contain all points above the threshold defined for a given isoline)*, contour-isobands-rs computes *isobands* (cf. wikipedia:Marchingsquares#Isobands) and their corresponding polygons (i.e. contour polygons that contain all points between a minimum and a maximum bound).

Depending on the desired use of the result, this contour-isobands crate may be more suitable than the contour crate (for example to visualize results with an opacity lower than 100%).

Licence

Since this is mostly a port of https://github.com/RaumZeit/MarchingSquares.js which is licenced under the Affero General Public License v3.0, this project is also licenced under the Affero General Public License v3.0. See the LICENSE file for details.