Abstract: A device executing intervisibility calculation includes a mechanism executing a radial spoke scan pattern where individual radials are traversed beginning at a threat installation and extending outward along a radial to a distance corresponding to threat range capability. Intervisibility calculation is simplified to allow implementation in a simple, dedicated hardware engine to provide rapid execution time while ensuring accurate intervisibility results. The intervisibility engine includes lookup tables to provide precalculated data and advantageously avoids divide operations whereby the intervisibility calculation may be executed by use of a series of adds, subtracts, and multiplies relative to intervisibility data developed while traversing a given radial. The engine calculates a slope for each data post visited in traversing a radial, and identifies a data post as being visible when its associated slope is greater than a previously encountered greatest magnitude slope.

Abstract: An apparatus for reading a first addressable memory and writing into a second addressable memory wherein the first addressable memory is logically arranged in a rectangular matrix and is scanned at an arbitrary angle with respect to the matrix for producing a plurality of scan patterns whose parameters can be altered and controlled by an external source, while the second addressable memory, also arranged in a rectangular matrix, is written into along parallel rows and columns. The apparatus is particularly adapted for use with a digital map display system having an airborne computer for generation the scan parameters.