Why Visibility?

• Terrain visibility determination is very important.
• ... but very compute intensive.
• Consider a 1201x1201 DEM with R=100. Ignoring edge effects, there are 3.14159 x 1201² 100² = 4.5e10 observer-target pairs.
• Let`s make this more efficient
• ... by studying relative importance of various factors.
• Looking at real data is always surprising.

Applications

• Siting cellphone towers.
• Locating a forest clearcut to be invisible to tourists driving along a highway that is itself sited to give a good view.
• Military observers.