XAML-Map-Control/MapControl/Shared/MapProjection.cs

// XAML Map Control - https://github.com/ClemensFischer/XAML-Map-Control
// © 2019 Clemens Fischer
// Licensed under the Microsoft Public License (Ms-PL)

using System;
#if WINDOWS_UWP
using Windows.Foundation;
using Windows.UI.Xaml.Media;
#else
using System.Windows;
using System.Windows.Media;
#endif

namespace MapControl
{
    /// <summary>
    /// Defines a map projection between geographic coordinates, cartesian map coordinates and viewport coordinates.
    /// </summary>
    public abstract class MapProjection
    {
        public const int TileSize = 256;
        public const double PixelPerDegree = TileSize / 360d;

        public const double Wgs84EquatorialRadius = 6378137d;
        public const double Wgs84Flattening = 1d / 298.257223563;
        public static readonly double Wgs84Eccentricity = Math.Sqrt((2d - Wgs84Flattening) * Wgs84Flattening);

        public const double Wgs84MetersPerDegree = Wgs84EquatorialRadius * Math.PI / 180d;

        /// <summary>
        /// Gets or sets the WMS 1.3.0 CRS Identifier.
        /// </summary>
        public string CrsId { get; set; }

        /// <summary>
        /// Indicates if this is a normal cylindrical projection.
        /// </summary>
        public bool IsNormalCylindrical { get; protected set; } = false;

        /// <summary>
        /// Indicates if this is a web mercator projection, i.e. compatible with MapTileLayer.
        /// </summary>
        public bool IsWebMercator { get; protected set; } = false;

        /// <summary>
        /// Gets the scale factor from geographic to cartesian coordinates, on the line of true scale of a
        /// cylindrical projection (usually the equator), or at the projection center of an azimuthal projection.
        /// </summary>
        public double TrueScale { get; protected set; } = Wgs84MetersPerDegree;

        /// <summary>
        /// Gets the absolute value of the minimum and maximum latitude that can be transformed.
        /// </summary>
        public double MaxLatitude { get; protected set; } = 90d;

        /// <summary>
        /// Gets the projection center. Only relevant for azimuthal pprojections.
        /// </summary>
        public Location ProjectionCenter { get; private set; } = new Location();

        /// <summary>
        /// Gets the transform matrix from cartesian map coordinates to viewport coordinates (pixels).
        /// </summary>
        public Matrix ViewportTransform { get; private set; }

        /// <summary>
        /// Gets the transform matrix from viewport coordinates (pixels) to cartesian map coordinates.
        /// </summary>
        public Matrix InverseViewportTransform { get; private set; }

        /// <summary>
        /// Gets the scaling factor from cartesian map coordinates to viewport coordinates (pixels)
        /// at the projection's point of true scale.
        /// </summary>
        public double ViewportScale { get; private set; }

        /// <summary>
        /// Gets the map scale at the specified Location as viewport coordinate units per meter (px/m).
        /// </summary>
        public virtual Vector GetMapScale(Location location)
        {
            return new Vector(ViewportScale, ViewportScale);
        }

        /// <summary>
        /// Transforms a Location in geographic coordinates to a Point in cartesian map coordinates.
        /// </summary>
        public abstract Point LocationToPoint(Location location);

        /// <summary>
        /// Transforms a Point in cartesian map coordinates to a Location in geographic coordinates.
        /// </summary>
        public abstract Location PointToLocation(Point point);

        /// <summary>
        /// Transforms a BoundingBox in geographic coordinates to a Rect in cartesian map coordinates.
        /// </summary>
        public virtual Rect BoundingBoxToRect(BoundingBox boundingBox)
        {
            return new Rect(
                LocationToPoint(new Location(boundingBox.South, boundingBox.West)),
                LocationToPoint(new Location(boundingBox.North, boundingBox.East)));
        }

        /// <summary>
        /// Transforms a Rect in cartesian map coordinates to a BoundingBox in geographic coordinates.
        /// </summary>
        public virtual BoundingBox RectToBoundingBox(Rect rect)
        {
            var sw = PointToLocation(new Point(rect.X, rect.Y));
            var ne = PointToLocation(new Point(rect.X + rect.Width, rect.Y + rect.Height));

            return new BoundingBox(sw.Latitude, sw.Longitude, ne.Latitude, ne.Longitude);
        }

        /// <summary>
        /// Transforms a Location in geographic coordinates to a Point in viewport coordinates.
        /// </summary>
        public Point LocationToViewportPoint(Location location)
        {
            return ViewportTransform.Transform(LocationToPoint(location));
        }

        /// <summary>
        /// Transforms a Point in viewport coordinates to a Location in geographic coordinates.
        /// </summary>
        public Location ViewportPointToLocation(Point point)
        {
            return PointToLocation(InverseViewportTransform.Transform(point));
        }

        /// <summary>
        /// Transforms a Rect in viewport coordinates to a BoundingBox in geographic coordinates.
        /// </summary>
        public BoundingBox ViewportRectToBoundingBox(Rect rect)
        {
            var transform = new MatrixTransform { Matrix = InverseViewportTransform };

            return RectToBoundingBox(transform.TransformBounds(rect));
        }

        /// <summary>
        /// Sets ProjectionCenter, ViewportScale, ViewportTransform and InverseViewportTransform.
        /// </summary>
        public void SetViewportTransform(Location projectionCenter, Location mapCenter, Point viewportCenter, double zoomLevel, double heading)
        {
            ProjectionCenter = projectionCenter;
            ViewportScale = Math.Pow(2d, zoomLevel) * PixelPerDegree / TrueScale;

            var center = LocationToPoint(mapCenter);
            var matrix = CreateTransformMatrix(center, ViewportScale, -ViewportScale, heading, viewportCenter);

            ViewportTransform = matrix;
            matrix.Invert();
            InverseViewportTransform = matrix;
        }

        internal static Matrix CreateTransformMatrix(
            Point translation1, double scale, double rotation, Point translation2)
        {
            return CreateTransformMatrix(translation1, scale, scale, rotation, translation2);
        }

        internal static Matrix CreateTransformMatrix(
            Point translation1, double scaleX, double scaleY, double rotation, Point translation2)
        {
            var matrix = new Matrix(scaleX, 0d, 0d, scaleY, -translation1.X * scaleX, -translation1.Y * scaleY);
            matrix.Rotate(rotation);
            matrix.Translate(translation2.X, translation2.Y);
            return matrix;
        }
    }
}