maptiles.cs

在windows mobile 5上的地图查看器

// Copyright (c) Jason Fuller. 
//
// Use of this source code is subject to the terms of the license found in the
// file License.txt.  If you did not accept the terms of that license, you are
// not authorized to use this source code.

#region Using directives

using System;
using System.Collections;
using System.Drawing;
using System.IO;
#endregion

namespace PocketEarth
{
    /// <summary>
    /// Summary description for MapTiles.
    /// </summary>
    public class MapTiles
    {
        /// <summary>
        /// MSN VirtualEarth version
        /// </summary>
        private const int tileVersion = 1;

        /// <summary>
        /// The width or height of one tile.
        /// </summary>
        public const int TileSize = 256;


        private static TileCache tileCache = new TileCache();

        private MapTiles()
        {
        }

        /// <summary>
        /// Remove any bitmaps from the cache that are not good.
        /// Good is defined as having been retrieved from the server.
        /// </summary>
        public static void PurgeBadBitmaps()
        {
            tileCache.PurgeBadBitmaps();
        }

        public static void PurgeAllBitmaps()
        {
            tileCache.PurgeAllBitmaps();
        }


        /// <summary>
        /// Gets a bitmap (possibly cached) for a map tile from 
        /// the VirtualEarth server.
        /// </summary>
        /// <param name="tx">tile X</param>
        /// <param name="ty">tile Y</param>
        /// <param name="zoomLevel">zoom level</param>
        /// <param name="mapStyle">map style</param>
        public static Bitmap GetMapTile(
            int tx,
            int ty,
            int zoomLevel,
            MapStyle mapStyle)
        {
            Bitmap tileBitmap = null;

            // Parameter checking
            int max = 1 << zoomLevel;
            if (tx < 0 || ty < 0 || tx >= max || ty >= max)
            {
                return null;
            }

            string url = BuildUrl(tx, ty, zoomLevel, mapStyle);

            // Look in the cache.
            tileBitmap = tileCache.LookupUrl(url);
            if (tileBitmap != null)
            {
                return tileBitmap;
            }


            return tileBitmap;
        }

        
        /// <summary>
        /// Convert a tile's xy coordinates to a quad key.
        /// A quad key is a string of base 4 digits.  The leftmost digit is
        /// which quadrant the tile is in at zoom level 1.  A quadrant has 4 
        /// cells laid out like this:
        /// 0 1
        /// 2 3
        /// The second digit is which quadrant within the first quadrant the 
        /// tile is.  And so on.
        /// The longer the string of digits, the more zoomed in the tile is.
        /// </summary>
        /// <param name="zoomLevel">zoom level</param>
        /// <param name="ty">tile Y</param>
        /// <param name="ty">tile Y</param>
        /// <returns>The quad key</returns>
        private static string TileToQuadKey(
            int tx, 
            int ty, 
            int zl)
        {
            string quad = "";
            for (int i = zl; i > 0; i--)
            {
                int mask = 1 << (i - 1);
                int cell = 0;
                if ((tx & mask) != 0)
                {
                    cell++;
                }
                if ((ty & mask) != 0)
                {
                    cell += 2;
                }
                quad += cell;
            }
            return quad;
        }


        /// <summary>
        /// Builds the URL for the image of the tile at (tx,ty)
        /// </summary>
        /// <param name="tx">tile X</param>
        /// <param name="ty">tileY</param>
        /// <param name="zoomLevel">zoom level</param>
        /// <param name="ms">map style</param>
        /// <returns>The URL</returns>
        private static string BuildUrl(
            int tx,
            int ty,
            int zoomLevel,
            MapStyle ms)
        {
            string[] tileUrlPrefixes = new string[4];
            // Simple load balancing
            tileUrlPrefixes[0] = "http://tiles0.virtualearth.msn.com/tiles/";
            tileUrlPrefixes[1] = "http://tiles1.virtualearth.msn.com/tiles/";
            tileUrlPrefixes[2] = "http://tiles2.virtualearth.msn.com/tiles/";
            tileUrlPrefixes[3] = "http://tiles3.virtualearth.msn.com/tiles/";
            int server = ((tx & 1) + ((ty & 1) << 1)) % tileUrlPrefixes.Length;

            return tileUrlPrefixes[server]
                    + (ms == MapStyle.Road ? 'r' :
                       ms == MapStyle.Aerial ? 'a' : 'h')
                    + TileToQuadKey(tx, ty, zoomLevel)
                    + (ms == MapStyle.Road ? ".png" : ".jpeg")
                    + "?g=" + MapTiles.tileVersion;
        }


    }
}