Map tile reader hierarchy

RasterMap has a reference to MapTileDownloadManager, which manages all map tile reader work threads.

Most map servers like Google, Microsoft, Yahoo uses follow map tiles system, these map server divides the whole map into 256X256 map tiles.

• MapTileAbstractReader is the common base class for all map tile readers, from the RasterMap prospective, there’s no difference for online map, stored map or vector map, they have each MapTileAbstractReader subclass to handle the differences for online map, stored map and vector map.
• VectorMapRender renders map image tiles from MapInfo compatible vector map data file.
• MapTileStreamReader reads map image tiles from an input stream (mostly from a local stored file).
• MapTileDownloader downloads map image tiles from map servers like Google Map, Microsoft Live Map, and Yahoo Map etc.
• MapDirectionRenderer renders routing direction map tile, Guidebee Map API internally use and is not exposed as public API.