This library computes contour polygons by applying meandering triangles to an array of points with arbitrary 2D coordinates (x, y) holding numeric values z. To compute contours on gridded coordinates, see d3-contour instead. To compute contours on geographic data, see d3.geoContour.

For examples, see the tricontours collection on Observable.

If you use npm, npm install d3-tricontour. You can also download the latest release on GitHub. For vanilla HTML in modern browsers, import d3-tricontour from Skypack:

<script type="module">
import {tricontour} from "https://cdn.skypack.dev/d3-tricontour@1";
</script>

For legacy environments, you can load d3-tricontour’s UMD bundle from an npm-based CDN such as jsDelivr; a d3 global is exported:

<script src="https://cdn.jsdelivr.net/npm/d3-scale@4"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-delaunay@6"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-tricontour@1"></script>
<script>

const tric = d3.tricontour();
const contours = tric([[0, 0, 1], [1, 1, 0], [2, 0, 1]]);
> Array(11) [ {type: "MultiPolygon", coordinates: Array(1), value: 0} … ]
  
</script>

The API of tricontour is similar to that of d3-contour:

# d3.tricontour() · Source, Examples

Constructs a new tricontour generator with the default settings.

# tricontour(data) · Examples

Returns an array of contours, one for each threshold. The contours are MultiPolygons in GeoJSON format, that contain all the points with a value larger than the threshold. The value is indicated as geometry.value.

The data is passed as an array of points, by default with the format [x, y, value].

# tricontour.contour(data[, threshold])

Returns a contour, as a MultiPolygon in GeoJSON format, containing all points with a value larger or equal to threshold. The threshold is indicated as geometry.value

# tricontour.contours(data)

Returns an iterable over the contours.

# tricontour.isobands(data)

Returns an iterable over the isobands: contours between pairs of consecutive threshold values v0 (inclusive) and v1 (exclusive). geometry.value is equal to v0, geometry.valueMax to v1.

# tricontour.x([x])

Sets the x accessor. Defaults to `d => d[0]`. If x is not given, returns the current x accessor.

# tricontour.y([y])

Sets the y accessor. Defaults to `d => d[1]`. If y is not given, returns the current y accessor.

# tricontour.value([value])

Sets the value accessor. Defaults to `d => d[2]`. Values must be defined and finite. If value is not given, returns the current value accessor.

# tricontour.thresholds([thresholds])

Sets the thresholds, either explicitly as an array of values, or as a count that will be passed to d3.ticks. If empty, returns the current thresholds.

The following are experimental

These methods are used in d3-geo-voronoi’s geoContour.

# tricontour.triangulate([triangulate])

Sets the triangulate function. Defaults to d3.Delaunay.from. See Reusing a tricontour triangulation and UK tricontour for detailed examples.

# tricontour.pointInterpolate([pointInterpolate])

Sets the pointInterpolate function. Arguments: i, j, 0≤a<1. Defaults to linear interpolation between the coordinates of points i and j.

# tricontour.ringsort([ringsort])

Sets the ringsort function.