Direct georeferencing in aerial photogrammetric mapping

Aerial photogrammetric mapping is a well-established industry. Its methods have been evolving progressively but not explosively over many decades. Entrenched, reliable procedures have been developed to overcome pitfalls along the processing chain, allowing the delivery of high quality mapping products. Understandably this has resulted in the entrenchment of most people thinking as they design, capture and adjust blocks of photographs. With Integrated GPS/INS technology, however, one can step outside of this "blocked-block" philosophy since the parameters of a camera's Exterior Orientation (EO) are computed directly. In many cases this means the photogrammetric procedures that were once followed verbatim can now be by-passed completely. The application of navigation technology to directly georeference imagery data is booming and the industry tends to furnish systems that require minimal input from the user. As these "measuring boxes" turn into black boxes and the length of the processing chain extends, the users may quickly find themselves lost in the complexity when something does not stand up to their expectations. Hence, understanding the technology fundamentals as well as its limits may save time and effort and may avoid surprises. The goal of this column is to facilitate the transition process when starting to apply direct georeferencing by GPS/INS to aerial film-based imagery.