/Branches/02/Source/Extensions/geoCache.Caches.Disk/VirtualEarthTileSystem.cs

//------------------------------------------------------------------------------

// <copyright file="VirtualEarthTileSystem.cs" company="Microsoft">

//     Copyright (c) 2006 Microsoft Corporation.  All rights reserved.

// </copyright>

//

// Source from http://msdn.microsoft.com/en-us/library/bb259689.aspx 

//------------------------------------------------------------------------------



using System;

using System.Text;



namespace Microsoft.MapPoint

{

    public static class VirtualEarthTileSystem

    {

        private const double EarthRadius = 6378137;

        private const double MinLatitude = -85.05112878;

        private const double MaxLatitude = 85.05112878;

        private const double MinLongitude = -180;

        private const double MaxLongitude = 180;





        /// <summary>

        /// Clips a number to the specified minimum and maximum values.

        /// </summary>

        /// <param name="n">The number to clip.</param>

        /// <param name="minValue">Minimum allowable value.</param>

        /// <param name="maxValue">Maximum allowable value.</param>

        /// <returns>The clipped value.</returns>

        private static double Clip(double n, double minValue, double maxValue)

        {

            return Math.Min(Math.Max(n, minValue), maxValue);

        }

        

        



        /// <summary>

        /// Determines the map width and height (in pixels) at a specified level

        /// of detail.

        /// </summary>

        /// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)

        /// to 23 (highest detail).</param>

        /// <returns>The map width and height in pixels.</returns>

        public static uint MapSize(int levelOfDetail)

        {

            return (uint) 256 << levelOfDetail;

        }







        /// <summary>

        /// Determines the ground resolution (in meters per pixel) at a specified

        /// latitude and level of detail.

        /// </summary>

        /// <param name="latitude">Latitude (in degrees) at which to measure the

        /// ground resolution.</param>

        /// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)

        /// to 23 (highest detail).</param>

        /// <returns>The ground resolution, in meters per pixel.</returns>

        public static double GroundResolution(double latitude, int levelOfDetail)

        {

            latitude = Clip(latitude, MinLatitude, MaxLatitude);

            return Math.Cos(latitude * Math.PI / 180) * 2 * Math.PI * EarthRadius /

                MapSize(levelOfDetail);

        }







        /// <summary>

        /// Determines the map scale at a specified latitude, level of detail,

        /// and screen resolution.

        /// </summary>

        /// <param name="latitude">Latitude (in degrees) at which to measure the

        /// map scale.</param>

        /// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)

        /// to 23 (highest detail).</param>

        /// <param name="screenDpi">Resolution of the screen, in dots per inch.</param>

        /// <returns>The map scale, expressed as the denominator N of the ratio 1 : N.</returns>

        public static double MapScale(double latitude, int levelOfDetail, int screenDpi)

        {

            return GroundResolution(latitude, levelOfDetail) * screenDpi / 0.0254;

        }







        /// <summary>

        /// Converts a point from latitude/longitude WGS-84 coordinates (in degrees)

        /// into pixel XY coordinates at a specified level of detail.

        /// </summary>

        /// <param name="latitude">Latitude of the point, in degrees.</param>

        /// <param name="longitude">Longitude of the point, in degrees.</param>

        /// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)

        /// to 23 (highest detail).</param>

        /// <param name="pixelX">Output parameter receiving the X coordinate in pixels.</param>

        /// <param name="pixelY">Output parameter receiving the Y coordinate in pixels.</param>

        public static void LatLongToPixelXY(double latitude, double longitude, int levelOfDetail,

            out int pixelX, out int pixelY)

        {

            latitude = Clip(latitude, MinLatitude, MaxLatitude);

            longitude = Clip(longitude, MinLongitude, MaxLongitude);



            double x = (longitude + 180) / 360; 

            double sinLatitude = Math.Sin(latitude * Math.PI / 180);

            double y = 0.5 - Math.Log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * Math.PI);



            uint mapSize = MapSize(levelOfDetail);

            pixelX = (int) Clip(x * mapSize + 0.5, 0, mapSize - 1);

            pixelY = (int) Clip(y * mapSize + 0.5, 0, mapSize - 1);

        }







        /// <summary>

        /// Converts pixel XY coordinates into tile XY coordinates.

        /// </summary>

        /// <param name="pixelX">Pixel X coordinate.</param>

        /// <param name="pixelY">Pixel Y coordinate.</param>

        /// <param name="tileX">Output parameter receiving the tile X coordinate.</param>

        /// <param name="tileY">Output parameter receiving the tile Y coordinate.</param>

        public static void PixelXYToTileXY(int pixelX, int pixelY, out int tileX, out int tileY)

        {

            tileX = pixelX / 256;

            tileY = pixelY / 256;

        }







        /// <summary>

        /// Converts tile XY coordinates into a QuadKey at a specified level of detail.

        /// </summary>

        /// <param name="tileX">Tile X coordinate.</param>

        /// <param name="tileY">Tile Y coordinate.</param>

        /// <param name="levelOfDetail">Level of detail, from 1 (lowest detail)

        /// to 23 (highest detail).</param>

        /// <returns>A string containing the QuadKey.</returns>

        public static string TileXYToQuadKey(int tileX, int tileY, int levelOfDetail)

        {

            var quadKey = new StringBuilder();

            for (int i = levelOfDetail; i > 0; i--)

            {

                char digit = '0';

                int mask = 1 << (i - 1);

                if ((tileX & mask) != 0)

                {

                    digit++;

                }

                if ((tileY & mask) != 0)

                {

                    digit++;

                    digit++;

                }

                quadKey.Append(digit);

            }

            return quadKey.ToString();

        }

    }

}