Realistic and immersive simulations of land, sea, and sky are requisite to the military use of visual simulation for mission planning. Until recently, the simulation of natural environments has been limited first of all by the pixel resolution of visual displays. Visual simulation of those natural environments has also been limited by the scarcity of detailed and accurate physical descriptions of them. Our aim has been to change all that. To this end, many of us have labored in adjacent fields of psych- ogy, engineering, human factors, and computer science. Our efforts in these areas were...