D3.js Delaunay.hullPolygon() Method

Last Updated : 07 Mar, 2024

The Delaunay.hullPolygon() Method returns the closed polygon [[x0, y0], [x1, y1], …, [x0, y0]] representing the convex hull.

Syntax:

Delaunay.hullPolygon()

Parameters:

This method takes no parameters.

Return Value:

This method returns an Array of polygons that represents a convex hull.

Example 1: The below code example shows the use of the d3.Delaunay.hullPolygon() method.

HTML

<!DOCTYPE html>
<html>
 
<head>
    <meta charset="utf-8">
    <script src="https://d3js.org/d3.v5.min.js"></script>
</head>
 
<body style="text-align: center;">
    <h1 style="text-align: center; color: green;">
        GeeksforGeeks
    </h1>
    <h3 style="text-align: center;">
        D3.js | d3.hullPolygon() Method
    </h3>
 
    <div id="app" style=
        "text-align: center; 
        margin-top: 20px; 
        font-size: 18px;">
    </div>
 
    <script type="module">
        import * as d3 from "https://cdn.skypack.dev/d3@7";
 
        const canvasWidth = 400;
        const canvasHeight = 300;
        const canvas = 
            document.createElement("canvas");
        const context = canvas.getContext("2d");
 
        canvas.width = canvasWidth;
        canvas.height = canvasHeight;
 
        const data = Array(50).fill()
            .map((_, i) => ({
                x: (i * canvasWidth) / 50,
                y: Math.random() * canvasHeight
            }));
 
        const voronoi = d3.Delaunay.from(data,
            (d) => d.x,
            (d) => d.y
        ).voronoi([0, 0, canvasWidth, canvasHeight]);
 
        context.clearRect(0, 0, canvasWidth, canvasHeight);
 
        context.fillStyle = "black";
        context.beginPath();
        voronoi.delaunay.renderPoints(context, 1);
        context.fill();
 
        context.lineWidth = 1.5;
        const segments = 
            voronoi.render().split(/M/).slice(1);
        for (const e of segments) {
            context.beginPath();
            context.strokeStyle = 
                d3.hsl(360 * Math.random(), 0.7, 0.5);
            context.stroke(new Path2D("M" + e));
        }
 
        const hull = voronoi.delaunay.hullPolygon();
 
        document.querySelector("#app").innerHTML =
            `Convex Hull: ${JSON.stringify(hull)}`;
 
        document.querySelector("#app").
            appendChild(canvas);
    </script>
</body>
 
</html>

Output:

Screenshot-2024-03-03-184851-(1)

Example 2: The below code demonstrates the use of D3.js HullPloygon() method to calculate the convex hull of a set of points.

HTML

<!DOCTYPE html>
<html>
 
<head>
    <meta charset="utf-8">
    <script src="https://d3js.org/d3.v7.min.js"></script>
</head>
 
<body style="text-align: center;">
    <h1 style="text-align: center; color: green;">
        GeeksforGeeks
    </h1>
    <h3 style="text-align: center;">
        D3.js | hullPolygon() Method
    </h3>
 
    <div id="app" style=
        "text-align: center; 
        margin-top: 20px;">
    </div>
 
    <script type="module">
        import * as d3 from "https://cdn.skypack.dev/d3@7";
 
        const width = 600;
        const height = 400;
 
        const points = Array.from({ length: 50 }, 
            () => [Math.random() * width, 
                Math.random() * height]);
 
        const delaunay = d3.Delaunay.from(points);
 
        const hull = delaunay.hullPolygon();
 
        const canvas = d3.select("#app")
            .append("canvas")
            .attr("width", width)
            .attr("height", height);
 
        const context = 
            canvas.node().getContext("2d");
 
        context.beginPath();
        delaunay.renderPoints(context);
        context.fillStyle = "black";
        context.fill();
 
        context.beginPath();
        context.strokeStyle = "blue";
        context.lineWidth = 2;
        context.moveTo(hull[0][0], hull[0][1]);
        for (const point of hull) {
            context.lineTo(point[0], point[1]);
        }
        context.closePath();
        context.stroke();
    </script>
</body>
 
</html>