Computes isorings and contour polygons by applying marching squares to a rectangular array of numeric values.
Outputs ring coordinates or polygons contours (represented using geo-types MultiPolygons).
For each threshold value, the contour polygon are representing the area where the input values are greater than or equal to the threshold value.
The generated contours can also easily be serialised to GeoJSON.
Note : This is a port of d3-contour.
Add this to your Cargo.toml:
toml
[dependencies]
contour = "0.9.0"
and this to your crate root:
rust
extern crate contour;
The API exposes:
- a ContourBuilder struct, which computes isorings coordinates for a Vec of threshold values and transform them either :
- in Contours (a type containing the threshold value and the geometry as a MultiPolygon, easily serializable to GeoJSON), or,
- in Lines (a type containing the threshold value and the geometry as a MultiLineString, easily serializable to GeoJSON).
contour_rings function, which computes isorings coordinates for a single threshold value (returns a Vec of rings coordinates - this is what is used internally by the ContourBuilder).ContourBuilder is the recommended way to use this crate, as it is more flexible and easier to use (it enables to specify the origin and the step of the grid, and to smooth the contours, while contour_rings only speak in grid coordinates and doesn't smooth the resulting rings).
Without defining origin and step:
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
With origin and step
```rust let c = ContourBuilder::new(10, 10, true) // x dim., y dim., smoothing .xstep(2) // The horizontal coordinate for the origin of the grid. .ystep(2) // The vertical coordinate for the origin of the grid. .xorigin(100) // The horizontal step for the grid .yorigin(200); // The vertical step for the grid
let res = c.contours(&[ 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., 0., 1., 0., 0., 0., 0., 0., 0., 1., 1., 0., 1., 0., 0., 0., 0., 0., 0., 1., 1., 0., 1., 0., 0., 0., 0., 0., 0., 1., 1., 0., 1., 0., 0., 0., 0., 0., 0., 1., 1., 0., 1., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0. ], &[0.5]).unwrap(); // values, thresholds
```
Using the geojson feature
The geojson feature is not enabled by default, so you need to specify it in your Cargo.toml:
toml
[dependencies]
contour = { version = "0.8.0", features = ["geojson"] }
```rust let c = ContourBuilder::new(10, 10, true) // x dim., y dim., smoothing .xstep(2) // The horizontal coordinate for the origin of the grid. .ystep(2) // The vertical coordinate for the origin of the grid. .xorigin(100) // The horizontal step for the grid .yorigin(200); // The vertical step for the grid
let res = c.contours(&[ 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., 0., 1., 0., 0., 0., 0., 0., 0., 1., 1., 0., 1., 0., 0., 0., 0., 0., 0., 1., 1., 0., 1., 0., 0., 0., 0., 0., 0., 1., 1., 0., 1., 0., 0., 0., 0., 0., 0., 1., 1., 0., 1., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0. ], &[0.5]).unwrap(); // values, thresholds println!("{:?}", res[0].to_geojson()); // prints the GeoJSON representation of the first contour ```
Output:
rust
Feature {
bbox: None,
geometry: Some(Geometry {
bbox: None,
value: MultiPolygon([
[[
[110.0, 215.0], [110.0, 213.0], [110.0, 211.0], [110.0, 209.0],
[110.0, 207.0], [109.0, 206.0], [107.0, 206.0], [106.0, 207.0],
[106.0, 209.0], [106.0, 211.0], [106.0, 213.0], [106.0, 215.0],
[107.0, 216.0], [109.0, 216.0], [110.0, 215.0]
]],
[[
[114.0, 215.0], [114.0, 213.0], [114.0, 211.0], [114.0, 209.0],
[114.0, 207.0], [113.0, 206.0], [112.0, 207.0], [112.0, 209.0],
[112.0, 211.0], [112.0, 213.0], [112.0, 215.0], [113.0, 216.0],
[114.0, 215.0]
]]
]),
foreign_members: None
}),
id: None,
properties: Some({"threshold": Number(0.5)}),
foreign_members: None
}
Demo of this crate compiled to WebAssembly and used from JavaScript : wasmdemocontour.
While this 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, the contour-isobands crate may be more suitable than this contour crate.
Licensed under either of
at your option.
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.