GeoServer基于Silverlight技术的地图客户端实现

一、DeepZoom简介

DeepZoom技术以MultiScaleImage控件为核心，其内部有一个 MultiScaleTileSource类型的源属性，主要用于设置MultiScaleImage 控件所要呈现的数据源。基于Silverlight的Web GIS客户端实现也是 通MultiScaleImage控件来实现，核心就在于通过MultiScaleTileSource 属性针对不同的Web GIS地图瓦片数据（Image Tiles）提供商为 MultiScaleImage控件实现一个数据源。这里做的工作就是针对WMS 服务为MultiScaleImage控件实现一套加载数据源的算法。

二、WMS服务加载实现

实现WMS服务加载的算法其实非常简单，只需要了解WMS发布的方式、 WMS地址的参数组成结构以及地图瓦片的投影原理就可以了，首先 需要定义一个盒子对象作为访问WMS的边界参数对象。

public class BBox
{
    public int X { get; set; }
    public int Y { get; set; }
    public int Width { get; set; }
    public int Height { get; set; }

    public BBox(int x, int y, int w, int h)
    {
        this.X = x;
        this.Y = y;
        this.Width = w;
        this.Height = h;
    }
}

关于WMS服务加载的详细算法需要一些GIS理论基础才能够知道具体的 实现原理，这里我就不逐一介绍，直接贴代码：

public class WMSTileSource : MultiScaleTileSource 
{
    public WMSTileSource()
        : base(int.MaxValue, int.MaxValue, 0x100, 0x100, 0)
    { }

    public const int TILE_SIZE = 256;
    /// 

    /// 地球半径
    /// 
    public const double EARTH_RADIUS = 6378137;
    /// 

    /// 地球周长
    /// 
    public const double EARTH_CIRCUMFERENCE = EARTH_RADIUS * 2 * Math.PI;
    public const double HALF_EARTH_CIRCUMFERENCE = EARTH_CIRCUMFERENCE / 2;

    /// 

    /// WMS服务地址
    /// 
    private const string TilePath = @"http://localhost:8080/geoserver/wms?service=WMS&version=1.1.0&request=GetMap&layers=cq:CQ_County_region,cq:CQ_County_region_level&styles=&bbox={0},{1},{2},{3}&width=512&height=421&srs=EPSG:4326&&Format=image/png";

    public string GetQuadKey(string url)
    {
        var regex = new Regex(".*tiles/(.+)[.].*");
        Match match = regex.Match(url);

        return match.Groups[1].ToString();
    }

    public BBox QuadKeyToBBox(string quadKey, int x, int y, int zoomLevel)
    {
        char c = quadKey[0];

        int tileSize = 2 << (18 - zoomLevel - 1);

        if (c == '0')
        {
            y = y - tileSize;
        }

        else if (c == '1')
        {
            y = y - tileSize;
            x = x + tileSize;
        }

        else if (c == '3')
        {
            x = x + tileSize;
        }

        if (quadKey.Length > 1)
        {
            return QuadKeyToBBox(quadKey.Substring(1), x, y, zoomLevel + 1);
        }
        return new BBox(x, y, tileSize, tileSize);
    }

    public BBox QuadKeyToBBox(string quadKey)
    {
        const int x = 0;
        const int y = 262144;
        return QuadKeyToBBox(quadKey, x, y, 1);
    }

    public double XToLongitudeAtZoom(int x, int zoom)
    {
        double arc = EARTH_CIRCUMFERENCE / ((1 << zoom) * TILE_SIZE);
        double metersX = (x * arc) - HALF_EARTH_CIRCUMFERENCE;
        double result = RadToDeg(metersX / EARTH_RADIUS);
        return result;
    }

    public double YToLatitudeAtZoom(int y, int zoom)
    {
        double arc = EARTH_CIRCUMFERENCE / ((1 << zoom) * TILE_SIZE);
        double metersY = HALF_EARTH_CIRCUMFERENCE - (y * arc);
        double a = Math.Exp(metersY * 2 / EARTH_RADIUS);
        double result = RadToDeg(Math.Asin((a - 1) / (a + 1)));
        return result;
    }

    public double RadToDeg(double d)
    {
        return d / Math.PI * 180.0;
    }

    private 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();
    }

    protected override void GetTileLayers(int tileLevel, int tilePositionX, int tilePositionY, System.Collections.Generic.IList