The Application of Augmented Reality to Reverse Camera Projection 2019-01-0424

In 1980, research by Thebert introduced the use of photography equipment and transparencies for onsite reverse camera projection photogrammetry [1]. This method involved taking a film photograph through the development process and creating a reduced size transparency to insert into the cameras viewfinder. The photographer was then able to see both the image contained on the transparency, as well as the actual scene directly through the cameras viewfinder. By properly matching the physical orientation and positioning of the camera it was possible to visually align the image on the image on the transparency to the physical world as viewed through the camera. The result was a solution for where the original camera would have been located when the photograph was taken. With the original camera reverse-located, any evidence in the transparency that is no longer present at the site could then be replaced to match the evidences location in the transparency. Reverse camera projection is useful for both determining the location of historical evidence, where it is no longer physically in existence, as well as for directing the investigator to evidence still at the site that may otherwise have been overlooked during a site inspection. With the advent of augmented reality, an entirely digital process of this technique is now possible. This paper both presents a digital methodology and provides reference to a publicly available, augmented reality application developed specifically for this process by the authors. The accuracy of the application and methodology is then demonstrated through field studies with reported results.