Earth Resource Mapping has recently completed a World Geocover Mosaic from Landsat satellite imagery. It is thought to be the world's largest image served over the Internet, and the largest image of the Earth. Over 600 separate images, each a mosaic of about 10 to 15 Landsat TM scenes, totalling two terabytes of imagery, was mosaiced and compressed using a pre-release version of ER Mapper 6.4.

The final mosaic covers almost the entire landmass of the planet Earth at 30 metre resolution. The image measures 1,4 million pixels wide by half a million pixels high. The 2 Terabytes of raw data has been compressed to an ECW (enhanced compression wavelet) file that is 26 Gigabytes in size - a compression ratio of 80:1.

Compression was performed using ER Mapper 6.4, which is shipping this month. Compression of this 2 TB world mosaic was made possible by new features in ER Mapper 6.4, including an enhanced compression engine allowing for faster compression of very large mosaics.

"Whilst geoscientists will be interested in the image due to the ability to differentiate rock types, urban areas, salt scald, fires, water and vegetation, the image also offers exciting prospects for the casual user. The high resolution of the image means that river deltas, river networks, mountain ranges, volcanoes and other landmarks can easily be detected," said Harold McMahon, senior image analyst.

The image can be viewed on the Web, using Earth Resource Mappings Image Web Server technology at http://www. earthetc.com/world/</a>

As well as direct Web browser access the image can be opened in desktop applications that natively support ECW files, or by downloading many of the free plug-ins available (such as a Microsoft office plug-in). Free plug-ins and a listing of applications that support ECW is available at www.ermapper.com/downloads

To directly open the image in an ECWP-aware application, use the following URL: ecwp://www.earthetc.com/images/geodetic/world/landsat742.ecw