function inertiaDrag(projection, render, started, moved, ended) {
    let v0, // Mouse position in Cartesian coordinates at start of drag gesture.
        r0, // Projection rotation as Euler angles at start.
        q0; // Projection rotation as versor at start.
    const limit = 1.0001;
    const A = 5000; // reference time in ms
    const B = -Math.log(1 - 1 / limit);
    const inertia = {
        start() {
            const position = d3.mouse(this);
            inertia.position = position;
            inertia.velocity = [0, 0];
            if (inertia.timer) {
                inertia.timer.stop();
            }
            // original start-drag
            v0 = versor.cartesian(projection.invert(position));
            r0 = projection.rotate();
            q0 = versor(r0);
            started && started.call(this, position);
        },
        move() {
            const position = d3.mouse(this);
            const time = performance.now();
            let timeGap = time - inertia.time;
            const decay = 1 - Math.exp(-timeGap / 1000);
            inertia.velocity = inertia.velocity.map(function(d, i) {
                const posGap = position[i] - inertia.position[i];
                const decay1 = 1 - decay;
                const decayD = d * decay;
                timeGap = time - inertia.time;
                return 1000 * decay1 * posGap / timeGap + decayD;
            });
            inertia.time = time;
            inertia.position = position;
            // original move-drag
            const inv = projection.rotate(r0).invert(position);
            if (isNaN(inv[0])) return;
            const v1 = versor.cartesian(inv),
                q1 = versor.multiply(q0, versor.delta(v0, v1)),
                r1 = versor.rotation(q1);
            render(r1);
            moved && moved.call(this, position);
        },
        end() {
            const v = inertia.velocity;
            if (v[0] * v[0] + v[1] * v[1] < 100) {
              	return;
            }  
            // versor velocity
            const p10 = inertia.position.map((d, i) => d - inertia.velocity[i] / 1000),
                v10 = versor.cartesian(projection.invert(p10)),
                r10 = projection.rotate(),
                q10 = versor(r10),
                p11 = inertia.position,
                v11 = versor.cartesian(projection.invert(p11));
            inertia.timer = d3.timer(function(e) {
                const t = inertia.t = limit * (1 - Math.exp(-B * e / A)),
                    q11 = versor.multiply(q10, versor.delta(v10, v11, t * 1000));
                r11 = versor.rotation(q11);
                render(r11);

                if (inertia.t > 1) {
                    inertia.timer.stop();
                    inertia.velocity = [0, 0];
                    inertia.t = 1;
                }
            });
            ended && ended.call(this, inertia.position);
        },
        position: [0, 0],
        velocity: [0, 0], // in pixels/s
        timer: null,
        time: 0,
    }
    return inertia;
};