DistanceTo.cs

        /// <summary>
        /// Obtains the distance between two points.
        /// </summary>
        /// <param name="u">Vector3.</param>
        /// <param name="v">Vector3.</param>
        /// <returns>Distance.</returns>
        public static double Distance(this XYZ u, XYZ v)
        {
            return u.DistanceTo(v);
        }

DistanceTo2.cs

        
        /// <summary>
        /// Obtains the distance between two points.
        /// </summary>
        /// <param name="u">Vector3.</param>
        /// <param name="v">Vector3.</param>
        /// <returns>Distance.</returns>
        public static double Distance(this XYZ u, XYZ v)
        {
            return Math.Sqrt(SquareDistance(u, v));
        }

        /// <summary>
        /// Obtains the square distance between two points.
        /// </summary>
        /// <param name="u">Vector3.</param>
        /// <param name="v">Vector3.</param>
        /// <returns>Square distance.</returns>
        public static double SquareDistance(this XYZ u, XYZ v)
        {
            return (u.X - v.X) * (u.X - v.X) + (u.Y - v.Y) * (u.Y - v.Y) + (u.Z - v.Z) * (u.Z - v.Z);
        }