LeapSample / HandRotationLeap

AppModel.cs

using System;
using System.Windows.Media.Media3D;

namespace HandRotationLeap
{
    public static class Leap3DHelper
    {
        public static Vector3D ToVector3D(this Leap.Vector v) => new Vector3D(v.x, v.y, v.z);

        // Wrong values.
        public static EulerAngles GetEulerAngles_org(this Leap.Hand h) => new EulerAngles
        {
            Yaw = h.Direction.Yaw,
            Pitch = h.Direction.Pitch,
            Roll = h.PalmNormal.Roll,
        };

        // Improved values.
        public static EulerAngles GetEulerAngles(this Leap.Hand h) =>
            Rotation3DHelper.ToEulerAngles(-h.Direction.ToVector3D(), -h.PalmNormal.ToVector3D());
    }
}

The whole source code is HandRotationLeap (GitHub).