Lens distortion simulation. An application for understanding geometric distortion

Abstract

The popularisation of photography as a documentary basis in the field of architectural and archaeological heritage recording, sustained by the development of more and more powerful computers and easy-to-use software tools, has brought as a consequence the popularisation of Photogrammetry. Simultaneously its happening the explosion of a technology phenomenon with positive and negative effects: The digital camera. Day by day they are becoming more capable, with higher resolution, smaller and cheaper. They are, without any doubt, the unavoidable successors of film cameras at any level. The new image sensors are being vastly and unceasingly improved. The professional branch evolves in the sense of raising the sizes up to the standard 36 x 24 mm with resolutions of over 10 Mpix, nearly able to fit into the usual SLR bodies but sadly by now at very high prizes. At the same time, in the consumer market, the sensors are being improved and becoming cheaper at sizes of about 1cm. For these, very small lens groups are needed, and for them almost microscopic focus mechanisms. This implies that high geometric image quality is very difficult to achieve. Even the best semi-professional digital cameras show very noticeable lens distortion and the images need to be corrected and thus resampled in order to have all of their potential benefits in the photogrammetric usage and particularly if they are taken for rectification purposes. The lens geometric distortion effects and their relation with the various mathematic expressions used for its characterisation, seems often too abstract for non-skilled users or better, for users that have not specific background in Optics, or Photogrammetry. For this reason, we have developed an application that is called LDS (by means of Lens Distortion Simulator) that we present as a tool for experimentation, simulation and correction of the lens geometric distortions in digital imagery. It is particularly oriented to academic scenarios and, in a more general point sense, to users and professional of Photogrammetry