Converting latitude and longitude to UTM using ProjNet

LLtoUTM.cs

/*
 * LL to UTM Converter
 * Copyright (C) 2016  Érycson Nóbrega <egdn2004@gmail.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

using System;

using GeoAPI.CoordinateSystems;
using GeoAPI.CoordinateSystems.Transformations;
using ProjNet.CoordinateSystems;
using ProjNet.CoordinateSystems.Transformations;

namespace LLtoUTM
{
    class WGS84Coordinate {
        public double Latitude;
        public double Longitude;
    }

    class UTMCoordinate {
        public double X;
        public double Y;
        public int Zone;
        public bool ZoneIsNorth;
    }

    class Program
    {
        static void Main(string[] args)
        {
            new Program();
        }

        public Program()
        {
            WGS84Coordinate ll = new WGS84Coordinate();
            ll.Latitude = -7.06965399;
            ll.Longitude = -34.84076309;

            UTMCoordinate _utm = LLtoUTM(ll);
            Console.WriteLine("{0}E {1}N", _utm.Y, _utm.X);

            WGS84Coordinate _ll = UTMtoLL(_utm);
            Console.WriteLine("Lat: {0} Lon: {1}", _ll.Latitude, _ll.Longitude);

            Console.ReadKey();
        }

        int GetZone(double latitude, double longitude)
        {
            if (latitude >= 56 && latitude < 64 && longitude >= 3 && longitude < 13)
                return 32;

            if (latitude >= 72 && latitude < 84)
            {
                if (longitude >= 0 && longitude < 9)
                    return 31;
                else if (longitude >= 9 && longitude < 21)
                    return 33;
                if (longitude >= 21 && longitude < 33)
                    return 35;
                if (longitude >= 33 && longitude < 42)
                    return 37;
            }

            return (int)Math.Ceiling((longitude + 180) / 6);
        }

        // http://romansk.blogspot.com.br/2013/09/converting-latitude-and-longitude-to.html
        UTMCoordinate LLtoUTM(WGS84Coordinate pos)
        {
            if (pos.Latitude < -80 || pos.Longitude > 84)
                throw new Exception();

            int zone = GetZone(pos.Latitude, pos.Longitude);

            CoordinateTransformationFactory ctfac = new CoordinateTransformationFactory();

            ICoordinateSystem wgs84 = ProjNet.CoordinateSystems.GeographicCoordinateSystem.WGS84;
            ICoordinateSystem utm = ProjNet.CoordinateSystems.ProjectedCoordinateSystem.WGS84_UTM(zone, pos.Latitude > 0);
            ICoordinateTransformation trans = ctfac.CreateFromCoordinateSystems(wgs84, utm);

            double[] result = trans.MathTransform.Transform(new double[] { pos.Longitude, pos.Latitude });
            return new UTMCoordinate {
                X = result[1], // N
                Y = result[0], // E
                Zone = zone,
                ZoneIsNorth = pos.Latitude > 0
            };
        }

        WGS84Coordinate UTMtoLL(UTMCoordinate pos) {
            CoordinateTransformationFactory ctfac = new CoordinateTransformationFactory();
            ICoordinateSystem wgs84 = ProjNet.CoordinateSystems.GeographicCoordinateSystem.WGS84;
            ICoordinateSystem utm = ProjNet.CoordinateSystems.ProjectedCoordinateSystem.WGS84_UTM(pos.Zone, pos.ZoneIsNorth);
            ICoordinateTransformation trans = ctfac.CreateFromCoordinateSystems(utm, wgs84);

            double[] result = trans.MathTransform.Transform(new double[] { pos.Y, pos.X });
            return new WGS84Coordinate
            {
                Latitude = result[1],
                Longitude = result[0]
            };
        }

    }
}