# d3-polygon

# d3-polygon

This module provides a few basic geometric operations for two-dimensional polygons. Each polygon is represented as an array of two-element arrays [[*x1*, *y1*], [*x2*, *y2*], …], and may either be closed (wherein the first and last point are the same) or open (wherein they are not). Typically polygons are in counterclockwise order, assuming a coordinate system where the origin ⟨0,0⟩ is in the top-left corner.

## Installing

If you use NPM, `npm install d3-polygon`

. Otherwise, download the latest release. You can also load directly from d3js.org, either as a standalone library or as part of D3 4.0. AMD, CommonJS, and vanilla environments are supported. In vanilla, a `d3`

global is exported:

```
<script src="https://d3js.org/d3-polygon.v1.min.js"></script>
<script>
var hull = d3.polygonHull(points);
</script>
```

Try d3-polygon in your browser.

## API Reference

Returns the signed area of the specified *polygon*. If the vertices of the polygon are in counterclockwise order (assuming a coordinate system where the origin ⟨0,0⟩ is in the top-left corner), the returned area is positive; otherwise it is negative, or zero.

# d3.**polygonCentroid**(*polygon*) <>

Returns the centroid of the specified *polygon*.

Returns the convex hull of the specified *points* using Andrew’s monotone chain algorithm. The returned hull is represented as an array containing a subset of the input *points* arranged in counterclockwise order. Returns null if *points* has fewer than three elements.

# d3.**polygonContains**(*polygon*, *point*) <>

Returns true if and only if the specified *point* is inside the specified *polygon*.

# d3.**polygonLength**(*polygon*) <>

Returns the length of the perimeter of the specified *polygon*.