LENS DISTORTION SIMULATION. AN APPLICATION FOR UNDERSTANDING 
GEOMETRIC DISTORTION. 
a Gómez Lahoz J. 
b Cuadrado Méndez 0. 
c Martinez Rubio J. 
a Salamanca University. School of Geodesy and Cartography Engineering. (Spain) 
b Cartography Service of Principality of Asturias. (Spain) 
c Valladolid University. School of Architecture. Laboratory of Photogrammetry. (Spain) 
Workgroup WG3 
KEY WORDS: digital cameras, interior parameters, lens distortion, camera calibration, rectification, geometric constraints. 
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. 
1. INTRODUCTION 
The progressive computerization of technologies, particularly 
since 1996, when digital photogrammetric workstations became 
well-settled, and with the boom of the World Wide Web, have 
given rise to the popularisation of Photogrammetry. 
We consider that this trend finds its raison d'etre and its better 
development space within the CIPA context. Lets highlight 
several facts that particularly sustain this appreciation. 
• The use of sensors that are more powerful and affordable 
day by day and thus well-suited for heritage recording 
purposes. (WG7). 
• The development and improvement of surveying methods 
that, with different accuracy and efficiency levels, have 
been applied to diverse fields embracing as different 
subjects as satellite imagery and tactile methods (WG3, 
WG6). 
• The availability of data processing tools have became 
more open, hybrid and less classic day by day : Today’s 
photogrammetric software tends to keep the General 
Method (that stands for the classic scheme of inner- 
relative-absolute orientations) away from the user and 
dissolved by the implementation of userfriendly 
interfaces. The same happens whith image processing and 
computer graphics (CAD) which are becoming more 
effective to render heritage objects (WG3,WG4). 
• The creation of meeting and discussion forums where 
different specialists can converge (bridge the gap) to a 
common objective (WG1.WG2). 
• The explicit impulse given to the “Photogrammetry for 
everyone”, which is best represented by proposals such as 
the “3x3 rules” (1988 Brunner-Waldhausl) that helps non- 
specialized people to get involved in heritage recording. 
(TGI). 
• The progressive rapprochement to photogrammetric 
concepts by an increasing number of people, thanks to the 
development of e-learning tools and the generalised 
Internet access. 
• The constant development of new applications to suit 
specific objectives is being possible thanks to the 
availability of easy to use and learn object oriented 
programming languages. These have allowed the user to 
customize his workspace and tools for each need. 
Within this panorama, our professional and teaching experience 
brings us many times to ask ourselves one question: Under what 
circumstances could we make use of non- calibrated cameras 
for heritage recording purposes?.