Compression of map images for real-time applications

Digital maps can be stored and distributed electronically using compressed raster image formats. We introduce a storage system for the map images that supports compact storage size, decompression of partial image, and smooth transitions between various scales. The main objective of the proposed storage system is to provide map images for real-time applications that use portable devices with low memory and computing resources. Compact storage size is achieved by dividing the maps into binary layers, which are compressed using context-based statistical modeling and arithmetic coding. Partial image decompression is supported by tiling the image into blocks and implementing direct access to the compressed blocks. In this paper, we give overview of the system architecture, describe the compression technique, and discuss implementation aspects. Experimental results are given both in terms of compression ratios and image retrieval timings. q 2004 Elsevier B.V. All rights reserved.