Abstract: A method to compress a very large original geographic database down to a manageable and economical size while preserving accuracy is herein described. Similarly, a method to quickly retrieve, decompress, and display data is herein described. An original geographic database is prepared for compression by dividing it into discrete regions called bounding boxes. The bounding boxes may be variable sized to improve accuracy and compression. Absolute map coordinate data is compressed by converting it to relative map coordinate data. Map files are named in a descriptive manner to allow determination of map file characteristics merely by inspecting the file name. Relative map coordinate data can be displayed without being converted to absolute map coordinate data. Alternately, relative map coordinate data may be quickly decompressed into absolute coordinate data. Retrieving compressed data is facilitated by forming view windows having adjacent load regions pre-decompressed and ready for user display.

Abstract: A hoisting system is disclosed which includes a hoisting drum around which two hoisting ropes are wound in respective hoist rope grooves. The hoisting ropes are secured to the hoisting drum at one end, and extend down to a suspended device, such as an elevator, or a crane hook. The hoisting drum also includes a cable groove, which is located between the two hoist rope grooves. An electrical cable is secured at one end to the hoist drum, is wound around the hoist drum in the cable groove, and extends down to the suspended device. A slip-ring assembly establishes an electrical connection to the cable, so as to permit power to be supplied to the suspended device.