PUSHBROOM ALGORITHMS FOR CALCULATING DISTANCES IN RASTER GRIDS

Distance and proximity are critical variables in many geo graphic analyses. In raster geographic analysis systems, distance is most commonly determined by a sequential growth process whereby distances are accumulated in radial bands from an initial set of features. While such procedures are very efficient for the generation of small buffer zones, they become cumbersome when large distance surfaces need to be determined. As an alternative, two "pushbroom" algo rithms are presented — one for the case of calculating true Euclidian distance over a plane, and a second for in corporating frictional effects in the generation of cost distance surfaces. In the former case, a complete surface of any size can be calculated in exactly four passes throu gh the data. In the second, as few as two complete passes are required, depending upon the nature of the frictional effects encountered. This economy arises from the nature of pushbroom techniques, whereby computations proceed sequen tially (not radially) through the raster grid, acquiring directionally-oriented knowledge in accordance with the di rection of the pushbroom path.