Triangulation of three points and radii

triangulate.js

function distance(p1, p2) {
    // Find the distance between two points
    return Math.sqrt(Math.pow(p2.x - p1.x, 2) + Math.pow(p2.y - p1.y, 2));
};

function intersect(c1, r1, c2, r2) {
    // Find the points of intersection for two circles
    // Based on: http://stackoverflow.com/a/3349134
    var d = distance(c1, c2);
    if (d > r1 + r2) // Circles do not overlap
        return [];
    if (d < Math.abs(r1 - r2)) // One circle contains the other
        return [];
    if (d == 0 && r1 == r2) // These are the same circles
        return [];

    // Find distances of dimensions from the first point
    var a = (Math.pow(r1, 2) - Math.pow(r2, 2) + Math.pow(d, 2)) / (2 * d);
    var h = Math.sqrt(Math.pow(r1, 2) - Math.pow(a, 2));

    // Determine point on the line between centers perpendicular to intersects
    var p = point(
        c1.x + a * (c2.x - c1.x) / d,
        c1.y + a * (c2.y - c1.y) / d
    );

    // Calculate intersection points
    return [
        point(
            p.x + h * (c2.y - c1.y) / d,
            p.y - h * (c2.x - c1.x) / d
        ),
        point(
            p.x - h * (c2.y - c1.y) / d,
            p.y + h * (c2.x - c1.x) / d
        )
    ];
};