XAML-Map-Control/MapControl/MapTransform.cs

// XAML Map Control - http://xamlmapcontrol.codeplex.com/
// © 2016 Clemens Fischer
// Licensed under the Microsoft Public License (Ms-PL)

#if NETFX_CORE
using System;
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 by the specified translation in viewport coordinates.
        /// </summary>
        public Location Transform(Location origin, Point mapOrigin, Point translation)
        {
#if NETFX_CORE
            var latitudeTranslation = translation.Y / RelativeScale(origin);

            if (Math.Abs(latitudeTranslation) < 1e-3) // avoid rounding errors
            {
                return new Location(origin.Latitude + latitudeTranslation, origin.Longitude + translation.X);
            }
#endif
            return Transform(new Point(mapOrigin.X + translation.X, mapOrigin.Y + translation.Y));
        }
    }

}