# 
[](https://www.npmjs.com/package/@thi.ng/geom-isoline)
[](https://mastodon.thi.ng/@toxi)
> [!NOTE]
> This is one of 205 standalone projects, maintained as part
> of the [@thi.ng/umbrella](https://github.com/thi-ng/umbrella/) monorepo
> and anti-framework.
>
> 🚀 Please help me to work full-time on these projects by [sponsoring me on
> GitHub](https://github.com/sponsors/postspectacular). Thank you! ❤️
- [About](#about)
- [Status](#status)
- [Installation](#installation)
- [Dependencies](#dependencies)
- [Usage examples](#usage-examples)
- [API](#api)
- [Authors](#authors)
- [License](#license)
## About
2D isoline / contour extraction, using [Marching
squares](https://en.wikipedia.org/wiki/Marching_squares). Ported from
the Clojure version of
[thi.ng/ndarray](https://github.com/thi-ng/ndarray/blob/develop/src/contours.org).
## Status
**STABLE** - used in production
[Search or submit any issues for this package](https://github.com/thi-ng/umbrella/issues?q=%5Bgeom-isoline%5D+in%3Atitle)
## Installation
```bash
yarn add @thi.ng/geom-isoline
```
ESM import:
```ts
import * as iso from "@thi.ng/geom-isoline";
```
Browser ESM import:
```html
```
[JSDelivr documentation](https://www.jsdelivr.com/)
For Node.js REPL:
```js
const iso = await import("@thi.ng/geom-isoline");
```
Package sizes (brotli'd, pre-treeshake): ESM: 716 bytes
## Dependencies
- [@thi.ng/api](https://github.com/thi-ng/umbrella/tree/develop/packages/api)
- [@thi.ng/transducers](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers)
- [@thi.ng/vectors](https://github.com/thi-ng/umbrella/tree/develop/packages/vectors)
Note: @thi.ng/api is in _most_ cases a type-only import (not used at runtime)
## Usage examples
One project in this repo's
[/examples](https://github.com/thi-ng/umbrella/tree/develop/examples)
directory is using this package:
| Screenshot | Description | Live demo | Source |
|:----------------------------------------------------------------------------------------------------------------|:-----------------------------------------------------------|:-------------------------------------------------|:------------------------------------------------------------------------------|
| 
| Animated sine plasma effect visualized using contour lines | [Demo](https://demo.thi.ng/umbrella/iso-plasma/) | [Source](https://github.com/thi-ng/umbrella/tree/develop/examples/iso-plasma) |
## API
[Generated API docs](https://docs.thi.ng/umbrella/geom-isoline/)
```ts
import * as g from "@thi.ng/geom";
import * as iso from "@thi.ng/geom-isoline";
import * as tx from "@thi.ng/transducers";
import * as fs "node:fs";
// evaluate fn for each [x,y], create array
const makeField = (fn, width, height) =>
iso.setBorder(
[...tx.map(fn, tx.range2d(width, height))],
width,
height,
1000
);
// precompute field with given fn
const src = makeField(
([x, y]) => Math.sin(x * 0.1) * Math.cos(y * 0.1),
100,
100
);
// contour iterator
const contours = tx.iterator(
tx.comp(
// iso value => RGB color from
tx.mapIndexed((i, x) => [x, [i / 20, 1 - i / 40, 1 - i / 20]]),
// contour & color tuples
tx.mapcat(([i, col]) => tx.map((pts)=> [pts, col], iso.isolines(src, 100, 100, i))),
// wrap as polygon for svg
tx.map(([pts, col]) => g.polygon(pts, { stroke: col}))
),
// iso value range
tx.range(-1, 1, 0.05)
);
// svg document wrapper
const doc = g.svgDoc(
{
width: 600,
height: 600,
fill: "none",
"stroke-width": 0.1
},
...contours
);
// output
fs.writeFileSync("contours.svg", g.asSvg(doc));
```
## Authors
- [Karsten Schmidt](https://thi.ng)
If this project contributes to an academic publication, please cite it as:
```bibtex
@misc{thing-geom-isoline,
title = "@thi.ng/geom-isoline",
author = "Karsten Schmidt",
note = "https://thi.ng/geom-isoline",
year = 2015
}
```
## License
© 2015 - 2025 Karsten Schmidt // Apache License 2.0