1. A topographic data processor comprising: means for selecting a pair of frames from a plurality of candidate picture frames of a target area captured from different high-altitude positions, said pair of frames constituting a stereoscopic image of said target area; means for determining a parallax between the selected frames and producing therefrom a first plurality of line-of-sight vectors and a second plurality of line-of-sight vectors; and means for converting said first and second pluralities of line-of-sight vectors to topographic data.