图片图层分两种，一种是动态图层，一种就是缓存图层。缓存图层就是已经切好图片，这种方式出图速度快，通常用作底图。关于图层相关概念请参考帮助文档《地图与图层》章节。

自定义缓存图层时，用户需要继承 TiledCachedLayer 类，Resolutions 和 Bounds 属性是必须设置的。如果是 SuperMap 切的图片，已知 Scales ，那么也要将 Scales 转成 Resolutions。最主要的是重写父类的 GetTileUrl 方法和 Initialize 方法，要在 Initialize 中获取必要的参数，在 GetTileUrl 中组织好对应缓存图片的 URL 。

下面是一个扩展 iServer2 缓存图片的例子。




  2. 代码实现：

C#

拷贝代码

public class CustomCachedLayer : TiledCachedLayer
{
    private string uriFormat;
    public CustomCachedLayer(string cachedUrl, Rectangle2D bounds, double[] scales, Rectangle2D referViewBounds, Rect referViewer, double referScale)
    {
        this.CachedUrl = cachedUrl;
        this.Bounds = bounds;
        this.Scales = scales;
        this.Dpi = ScaleHelper.GetSmDpi(referViewBounds, referViewer, referScale);
        double[] resolutions = new double[scales.Length];
        for (int i = 0; i < scales.Length; i++)
        {
            resolutions[i] = ScaleHelper.ScaleConversion(scales[i], this.Dpi);
        }
        this.Resolutions = resolutions;
    }
    public override string GetTileUrl(int indexX, int indexY, int level)
    {
        string uri = string.Empty;
        if (!string.IsNullOrEmpty(this.uriFormat))
        {
            double scale = 1 / Scales[level];
            uri = String.Format(this.uriFormat, scale, indexX, indexY);
        }
        return uri;
    }
    public override void Initialize()
    {
        StringBuilder builder = new StringBuilder();
        builder.Append(this.CachedUrl);
        builder.AppendFormat("/{0}_{1}x{1}", this.MapName, 512);
        builder.Append("/{0}/{1}/{2}.");
        builder.AppendFormat("{0}", ImageFormat);
        this.uriFormat = builder.ToString();
        base.Initialize();
    }
    public string CachedUrl { get; set; }
    public string MapName { get; set; }
    private double[] scales = null;
    public double[] Scales
    {
        get { return scales; }
        set
        {
            if (value[0] > 1)
            {
                for (int i = 0; i < value.Length; i++)
                {
                    value[i] = 1.0 / value[i];
                }
            }
            scales = value;
        }
    }
}




  2. 定义 CustomCachedLayer 类之后，下面介绍一下使用方法。以下数据必须已知，可以从 Deskpro 中或调用 GetMapStatus 获取：

C#

拷贝代码

string cachedurl="http://localhost:7080/output";
  Rectangle2D bounds = new Rectangle2D(-180, -90, 180, 90);
  double[] scales = new double[] { 500000, 5000000, 50000000, 500000000 };
  Rectangle2D  referViewBounds=new Rectangle2D(-66.6154069176247, -49.9740487003936,  66.6154069176247, 49.9740487003936);
  Rect referViewer = new Rect(-31984, -31976, 400, 300);
  double  referScale = 0.000000008987817752221122;
  CustomCachedLayer clayer = new CustomCachedLayer(cachedurl, bounds, scales, referViewBounds,  referViewer, referScale);
  clayer.Url = "http://localhost:7080/demo";
  clayer.MapName = "World";
  MyMap.Layers.Add(clayer);