The Tri-Met System of Aerial Charting: A Working Manual for the Tri-Metrogon Process (Restricted) By Sixth Photographic Squadron (compilation) Books / Paperback History: World › Maps, Geography, Cartography Publisher: Army Air Forces, Price $37.58 Free Shipping Send to a friend Used - Good Good condition. Lower corner curled. (aerial topographic photography, mapping) $37.58 1 in Stock at Warehouse Quantity Add Free Shipping to continental U.S. OR $1.00 per item discount if shipped to store.