在geoserver中图像格式的数据说明，摘录的：
ImageMosaic = Stores more than one image - ImageMosaic data store allows the creation of a mosaic
WorldImage = Georeferencing file (plain text file with coordinates and pixel resolution)
ImagePyramid = image pyramid builds multiple mosaics of images, each one at a different zoom level, making it so that each tile is stored in a separate file. Can speed up image handling.
world file的详细介绍：http://en.wikipedia.org/wiki/World_file