 Because "Olympus Has Fallen" was filmed so far from its actual setting of Washington, D.C., the entire production relied heavily upon visual effects, particularly computer-generated imagery.For example, computers were used to create nearly all of the opening sequence in which the First Lady is killed in a car accident, with chroma key greenscreen technology used to composite the actors into the computer-generated snowy scenery.For scenes where actors walked in or out of the White House, a first-floor façade and entrance were built; computers added the second floor, roof, and downtown D.C. cityscape.