XAML-Map-Control/MapControl/MapTransform.cs

// XAML Map Control - http://xamlmapcontrol.codeplex.com/
// Copyright © 2014 Clemens Fischer
// Licensed under the Microsoft Public License (Ms-PL)

#if NETFX_CORE
using Windows.Foundation;
#else
using System.Windows;
#endif

namespace MapControl
{
    /// <summary>
    /// Defines a normal cylindrical projection. Latitude and longitude values in degrees are
    /// transformed to cartesian coordinates with origin at latitude = 0 and longitude = 0.
    /// Longitude values are transformed identically to x values in the interval [-180 .. 180].
    /// Latitude values in the interval [-MaxLatitude .. MaxLatitude] are transformed to y values in
    /// the interval [-180 .. 180] according to the actual projection, e.g. the Mercator projection.
    /// </summary>
    public abstract class MapTransform
    {
        /// <summary>
        /// Gets the absolute value of the minimum and maximum latitude that can be transformed.
        /// </summary>
        public abstract double MaxLatitude { get; }

        /// <summary>
        /// Gets the scale factor of the map projection at the specified geographic location
        /// relative to the scale at latitude zero.
        /// </summary>
        public abstract double RelativeScale(Location location);

        /// <summary>
        /// Transforms a geographic location to a cartesian coordinate point.
        /// </summary>
        public abstract Point Transform(Location location);

        /// <summary>
        /// Transforms a cartesian coordinate point to a geographic location.
        /// </summary>
        public abstract Location Transform(Point point);

        /// <summary>
        /// Transforms a geographic location to a cartesian coordinate point
        /// with minumum distance to the specified reference longitude value.
        /// </summary>
        public Point Transform(Location location, double referenceLongitude)
        {
            var p = Transform(location);

            p.X = Location.NormalizeLongitude(p.X);

            if (p.X > referenceLongitude + 180d)
            {
                p.X -= 360d;
            }
            else if (p.X < referenceLongitude - 180d)
            {
                p.X += 360d;
            }

            return p;
        }
    }
}