XAML-Map-Control/MapProjections/Shared/AutoUtmProjection.cs

// XAML Map Control - https://github.com/ClemensFischer/XAML-Map-Control
// © 2022 Clemens Fischer
// Licensed under the Microsoft Public License (Ms-PL)

using ProjNet.CoordinateSystems;
using System;
using System.Windows;

namespace MapControl.Projections
{
    public class AutoUtmProjection : GeoApiProjection
    {
        public const string DefaultCrsId = "AUTO2:42001";

        public int ZoneNumber { get; private set; }
        public bool ZoneIsNorth { get; private set; }

        public AutoUtmProjection()
        {
            UpdateZone();
        }

        public bool UseZoneCrsId { get; set; }

        public override Point? LocationToMap(Location location)
        {
            UpdateZone();

            return base.LocationToMap(location);
        }

        public override Location MapToLocation(Point point)
        {
            UpdateZone();

            return base.MapToLocation(point);
        }

        private void UpdateZone()
        {
            var north = Center.Latitude >= 0d;
            var lon = Location.NormalizeLongitude(Center.Longitude);
            var zone = (int)Math.Floor(lon / 6d) + 31;

            if (ZoneNumber != zone || ZoneIsNorth != north)
            {
                ZoneNumber = zone;
                ZoneIsNorth = north;

                CoordinateSystem = ProjectedCoordinateSystem.WGS84_UTM(ZoneNumber, ZoneIsNorth);

                if (!UseZoneCrsId)
                {
                    CrsId = DefaultCrsId;
                }
            }
        }
    }
}