Determining the Vertical Line from Zapruder in Willis 5

Oops Oops
Determining to which Zapruder frame the Willis slide corresponds is made much easier by  Willis appearing in the Zapruder film, Zapruder being visible in the Willis slide, and the motorcade passing between them.  This allows the construction of a plane between the center of the two cameras which appears in the images as a line because it is being viewed edge on.  The plane does not have to be vertical to make a comparison.  It just has to be the same plane in each image but it is generally easier to determine the vertical plane.  The Willis slide has the Dealey Plaza pergola in the background which has a number of vertical features.  Parallel lines converge to a "vanishing point" in a photo unless they are perpendicular to the direction the camera is pointed.  With vertical lines this is only true if the camera is pointed horizontally. Willis was pointing the camera slightly downward.  In this case lines that are vertical in the world point in different directions in different parts of the image and only the (world) vertical line that passes through the center of the  image is vertical in the image. (After leveling the image) We need to draw a vertical line, representing a vertical plane, from Zapruder's camera.  This can be done by determining the vanishing point from vertical features in the image and then drawing a line from Zapruder's camera to the vanishing point.  The image on the upper right shows the (true) vertical lines from the references to the vanishing point in black and the vertical computed for Zapruder in red. The vanishing point lies far below the image as shown in the drawing on the left.  Remember, the red line is really a vertical plane passing through the center of Zapruder's and Willis' cameras.  The plane passes through the left edge of Clint Hill (sorry, Clint) standing on the running board so we can use this information to determine the corresponding Zapruder frame. It really does not matter how the image is rotated in 2d since the lines rotate with the image, but I think a leveled picture looks better and the Zapruder frames are level so I provided a leveled image with just the vertical from Zapruder drawn. (lower right)