Secrets of a Homicide: Key Framing
Aligning 3D models with the Zapruder film
The crime scene recreation process begins by matching the speed of the limousine model to the Zapruder film.

The virtual camera is mounted at Zapruder's position and the first frame of the Zapruder film is superimposed over the scene. The view is adjusted until all fixed objects align with their virtual counterparts.

The ghosted shape of the limousine now reveals its position on the computer model of Elm Street. Using this image as a guide, the 3D limousine model is moved to the same spot, then keyed - or "locked" - into position at this specific moment in time.

The Zapruder film is advanced a short interval of time and the process is repeated until the entire limousine path is keyed into the computer. A test rendering is produced to check the speed of the model relative to the film. Lampposts along Elm Street, whose positions were triangulated to match their 1963 positions, are used as check points.

The limousine should pass each lamppost at precise intervals to match the Zapruder film. For this earliest test, all motion paths are left at linear positions. The test render shows that the 3D model's speed does not match the speed of the limousine seen in the Zapruder film. This, of course, is anticipated since the use of linear motion cannot compensate for changes in the limousine's speed as it progresses down Elm Street.

Spline motion paths are now employed to bring the limousine into line with the original film. This is mostly a matter of trial and error until a match is obtained.
adjusting the speed of the limousine
The result found the limousine decelerating immediately after Zapruder frame 223 until just after the head shot, at which point it accelerates until it disappears under the Triple Underpass. Now that the virtual limousine matches the position and motion of the presidential limousine in the Zapruder film, the process of keying the occupants can begin.

aligning Zapruder frame 225 The film is returned to the first frame showing the president and the same process used to match the limousine to the film is used to position President Kennedy (JFK) and Governor John B. Connally (JBC).

The ability to accurately position both men is directly related to the clarity of the original film. At the earliest portion of the Zapruder film, the limousine is at its farthest point from Zapruder's lens. The images of both JFK and JBC are very small in the frame and consequently distorted by film grain. As the limousine draws closer to the camera, they grow larger within the frame and therefore are distorted less by film grain.

From about Zapruder frame 240 through 360, the effect of film grain on the ability to position the occupants in the car accurately is negligible. At their farthest point from Zapruder's camera, it was possible to rotate both JFK and JBC up to 6-degrees in any direction without a perceivable mismatch with the original film. This amount of error dropped to about 4-degrees by Zapruder frame 190 and within 3-degrees by Zapruder frame 223. Therefore, the estimated margin of error lies between 3 and 6-degrees, depending on which point in the film is under discussion. The larger figure was used to calculate potential errors in plotting trajectories.
aligning models to Zapruder frame 225

The clearest frames of the Zapruder film were sought for positioning JFK and JBC in order to minimize any errors. Key frame positions were generally placed at half-second intervals throughout the recreation, although tighter keying patterns (1-5 frame intervals) were employed during Zapruder frames 220-238, and 312-330.

The resulting animation was spot checked against the original Zapruder film to insure an accurate representation. Where "drifting" was detected, additional key frames were used to nail down the action.

It took six weeks to complete the key frame process, after which a test render was produced. The resulting animation was a computer generated "hand-held" version of the Zapruder film. In essence, the key frame process had created a motion file of Zapruder's camera in 3D space. Stepping through each frame of the animation revealed how Zapruder held his camera while trying to follow the limousine as it moved down Elm Street.

Computer view of the limo on Houston Street The next step in the animation process was to recreate the portion of the motorcade that preceded Zapruder's film - from the corner of Main and Houston Streets to Zapruder's first frame.

The process utilized was nearly identical to that described earlier. Still photographs and amateur movie films taken along this portion of the route were used to position the limousine and its occupants. A triangulation of the available amateur movie films was the basis for establishing the precise speed and position of the limousine as it traversed this pre-Zapruder film portion of the motorcade route.

The large, and often overlapping, still and motion picture record of the motorcade between Main and Houston Streets and the point at which Zapruder began filming, provided an accurate and definitive record of the positions of JFK and JBC during this pre-shooting portion of the recreation.

The final step in the animation process was to generate a smooth sequence of images. Unlike Zapruder, the computer has the ability to lock its virtual camera onto a target without the imperfections a handheld or tripod mounted camera would produce. The result is an incredibly clear and accurate view of the assassination of President Kennedy.


Secrets of a Homicide: JFK Assassination © 1995-2008 Dale K. Myers. All Rights Reserved.
Published by Oak Cliff Press, Inc., P.O. Box 608, Milford, MI 48381-0608