Data compression

Compression of digitized pictorial data is achieved by comparing a data block of a predetermined size with a group of patterns relevant to that size held in a library. If a match is found the data block is represented by an output signal by a code identifying the pattern. If no match is found the data block is sub- divided into smaller blocks which are compared with another group of patterns. This sub-division process continues until the data is matched or a predetermined minimum size of data block is reached, when the data itself is applied to the output signal. The compressed data may be reconstituted and displayed or used to monitor the progress of a vehicle.