GB1485799A - Methods of encoding and storing data items - Google Patents

Abstract

1485799 Determining spatial relationships IBM UNITED KINGDOM Ltd 27 Dec 1974 55910/74 Heading G4A Spatial relationships between areas, lines and points may be determined by encoding the locations of the areas, lines and points from a map 10, Fig. 1, into data items consisting of Cartesian co-ordinate references of the locations by means of a digitizer 11, the data items being entered, together with associated information (such as addresses of buildings along a road) from blocks 12, 13 into a general purpose digital computer 15, the data items being encoded into bit strings which are stored in a data base 16, each bit string being representative of a location on the map. The invention permits digital comparisons to be made between the stored bit strings which enable the following problems to be solved: (a) does a point lie on a line or in an area, (b) does a line cross another line or pass through an area, or (c) does an area include a region within itself which does not occur in another area? The encoding performed by the digital computer 15 is carried out by successively dividing the map into quadrants, Fig. 3A, until the required degree of accuracy has been reached, a two-bit code being generated for each quadrant, which code is (a) 00 if none of the quadrant is shared, (b) 01 if part of the quadrant is shared, or (c) 10 if all of the quadrant is shared with an area, line or point. A bit string is generated by starting at the top left hand corner of block 30 and, proceeding clockwise, writing down the two-bit code for each quadrant in the block. Thus for block 30 the code is 01010101. Each quadrant for which a code of 01 has been generated is subdivided, as in block 31, and the codes written down for these subdivisions in the same manner. Thus for block 31 the code is 01010101000001011001010101010100. Quadrants for which the code is 00 or 10 generate a similar code if subdivided and hence are not considered again. These encoding steps are given in the flowcharts of Figs. 4A, 4B, 4C and 4D (not shown). The first few bits of each bit string may be processed to obtain a location for the bit string in the data base 16, so that objects close together on the map have their respective bit strings stored in physically near locations in the data base, in order to reduce processing time. The stored bit strings may be processed for display on a domestic television receiver. An error checking procedure given in Fig. 5 (not shown) may check each bit string for error conditions, e.g. a generated two-bit code of 11. Applications of the invention to calculations of the numerical area or centre of gravity of an encoded area are described. In modifications, equilateral triangular regions instead of quadrants or a code of more than two bits for each quadrant may be used.