Martin Smith
ABSOLUTE AND EXTERIOR ORIENTATION USING LINEAR FEATURES
Martin J. SMITH, David W. G. PARK
Institute of Engineering Surveying and Geodesy
The University of Nottingham, UK
martin.smith @nottingham.ac.uk
david.park @nottingham.ac.uk
Working Group IC/11
KEY WORDS: Orientation, photogrammetry, algorithms, geo-referencing, image registration, image mapping.
ABSTRACT
For many years we have had digital photogrammetric systems available that can perform automatic interior and relative
orientation of aerial photographs. Developments in absolute and exterior orientation are not so robust because the
problem is significantly more difficult. The reason for the increase in difficulty is that there is no easy way to create the
master image or target patch which represents the traditional ground control point. If we have such an image then there
are a number of techniques that are well established to undertake area or feature based matching to find the
corresponding point on the photograph. There are also an increasing number of users of photogrammetric techniques
and software who would like to be able to provide control for absolute or exterior orientation in a very easy and efficient
way without having to rely on careful identification of ground control points. These two issues have been the motivation
to investigate the general issue of improving the flexibility and ease of providing ground control for the processes of
absolute and exterior orientation using analytical and digital techniques.
This paper will present a new approach to absolute and exterior orientation based on the measurement of linear features
and their automatic matching. The results show that the technique can produce results suitable for many environmental
mapping applications and in some instances is suitable for topographic mapping. It is also shown to have the capability
of automatic relative orientation.
1 INTRODUCTION
1.1 Digital Photogrammetry
The advances in digital photogrammetry have brought many changes to traditional photogrammetric procedures and
products. Although these advances are bringing exciting changes to the users of photogrammetry there is still a role for
analytical photogrammetry to play, particularly in traditional vector mapping and in many special engineering
applications. Perhaps the most important benefit brought by digital photogrammetry is the potential for automation.
Having the photographs in digital image format provides them in a suitable form for computer manipulation and
processing. Automation is important for a number of reasons although the main drive is the quest to bring about
productivity gains by reducing the time taken to perform a task. From the point of view of job satisfaction there are
mixed feelings, as automation can remove the monotony and tedium of a repetitive task. For example digital elevation
observation can de-skill a task such as performing relative orientation or leave the photogrammetrist to clear up the
problems of unsatisfactory matching in digital elevation modelling (DEM) generation during quality control. There are
some tasks where automation can bring consistency of observation and quality. This might be noticeable when a human
Observer tires and for example may result in a reduction in their ability to perform relative orientation.
One of the side effects of introducing automation and de-skilling the tasks is that it enables a wider group of people to
use the techniques, largely as tools. Many traditionally accepted photogrammetric techniques are being included in
standard remote sensing image processing software. These can now be seen and used as tools by a non-specialist
photogrammetric community. It is easy to see that this will increase in the future. This ‘non-specialist’ group might
include geologists and environmental managers, it might also include archeologists, geographers, planners and users of
remote sensing. To these users, the highest metric accuracy is often not of major concern as the nature of the detail
/information being extracted is not accurately definable, it is typically ‘soft’ detail. What is important to these users is
that the tools must be easy to use, with minimal ‘specialized’ skill required.
850 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000.
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