Imagery makes up a large percentage of geospatial data in use today. One feature of this imagery is that it tends to be large, often hundreds or thousands of megabytes. As a result JPEG compression is often used to make geospatial imagery manageable by reducing the file size without greatly reducing the quality of the image. However, the benefits of compression are absent when the image must be viewed. Viewing a large JPEG image requires decompressing and holding the uncompressed version in memory. Holding the entirety of a large image in memory is a burden on many systems and sometimes impossible. However, the entire image is rarely needed at full resolution. Usually only a small area of interest is viewed or processed. This paper describes a method of removing a small area of interest from a large JPEG without decompressing the entire image. JPEG compressed images are streams which cannot be randomly accessed. Viewing a particular area requires that all preceding areas be partially decompressed. This process is more efficient than fully decompressing the whole JPEG, but depending on the area requested the entire image may need to be partially decompressed. To circumvent this problem an index file is created on first decompression which records markers for the sections of the JPEG. The index file allows random access to the JPEG file so that areas may be decompressed without reading the preceding portions of the JPEG. This method of decompressing a JPEG requires a limited amount of memory and with an index file is fast enough to be performed in real time.
The Naval Research Laboratory’s Geospatial Information Database (GIDB<sup>TM</sup>) Portal System has been extended to now include an extensive geospatial search functionality. The GIDB Portal System interconnects over 600 distributed geospatial data sources via the Internet with a thick client, thin client and a PDA client. As the GIDB Portal System has rapidly grown over the last two years (adding hundreds of geospatial sources), the obvious requirement has arisen to more effectively mine the interconnected sources in near real-time. How the GIDB Search addresses this issue is the prime focus of this paper.
The National Guard Bureau (NGB) and the Naval Research Lab (NRL) have developed a Digital Mapping System (DMS) Portal System that currently connects over 360 geospatial data servers. The DMS Portal System is located at http://ngbcdmaps.gtri.gatech.edu and is being used by nationwide law enforcement (approximately 5000 users/month) to generate geospatial mapping solutions to satisfy broad requirements with no licensing required. This paper will highlight the current functionality of the DMS Portal System to allow many types of geospatial information (such as weather, conventional maps, imagery, plume model dispersions, etc.) to appear in a common environment regardless of how the information is originally stored. The DMS Portal System has substantial potential usage in the homeland defense arena as well as with conventional DoD/government and private sector users. Future directions for this cutting-edge technology will be outlined.