3-D MODELLING OF HISTORICAL SITES USING LOW-COST DIGITAL CAMERAS
A. F. Habib“, M. S. Ghanma*, R. I. Al-Ruzouq”, E. M. Kim?
* Department of Geomatics Engineering, University of Calgary
2500, University Drive NW, Calgary AB T2N 1N4 Canada - (habib, mghanma, al-ruzouq)@geomatics.ucalgary.ca,
emkim@ucalgary.ca
SS4 - CIPA - Low-Cost Systems in Recording and Managing the Cultural Heritage
KEY WORDS: Camera, feature, CAD, modelling, reconstruction, cultural heritage.
ABSTRACT:
Photogrammetry is the art and science of deriving accurate 3-D metric and descriptive object information from multiple analogue
and digital images. Recently, there has been an increasing interest in utilizing imagery in different fields such as archaeology,
architecture, mechanical inspection, and surgery. The availability of reasonably priced, off-the-shelf, and high-quality digital
cameras is encouraging such interest. Any camera needs to be accurately calibrated and tested before it can be used for accurate
derivation of 3-D information. Traditional camera calibration is performed by qualified and trained professionals using a test field
with numerous control points (i.e., points with known ground coordinates). To expedite the process of camera calibration, this paper
outlines a new approach that is based on linear features within an easy-to-establish test field. Therefore, non-photogrammetrists can
utilize the new calibration procedure with the least effort. Moreover, the simplicity of the calibration procedure allows for the
evaluation of the camera stability through analyzing the estimated internal characteristics of the implemented camera from repetitive
calibration sessions. The proposed technique is considerably more flexible and possesses higher degree of robustness when
compared with traditional camera calibration exercises. The introduced calibration methodology allows for the utilization of digital
cameras in a vast range of application areas (e.g., three dimensional archiving of models and monuments as well as the capability of
generating 3-D perspective views). This paper introduces the calibration procedure, some analysis of the expected accuracy, and the
suggested methodology for 3-D modelling of historical sites. Experimental results using real data proved the feasibility and the
quality of the outcome from the suggested approach.
1. INTRODUCTION
Photogrammetry is concerned with deriving measurements of
the size, shape and position of objects from measurements made
on photographs. In its simplest form, a pair of overlapping
photographs is used to create a three-dimensional model, which
with the use of appropriate instrumentation can yield
quantifiable dimensions of the object. Traditionally, these
dimensions were represented on maps and plans, either as
elevations, facades and/or contours. The use of photogrammetry
as a tool to aid in the documentation of cultural heritage has a
long history, and is well established as a measurement science.
Recent advances in the science make the techniques much more
flexible in their application and present new opportunities in the
representation of monuments as diverse as aboriginal rock
painting shelters, historically significant buildings and
structures, and culturally significant precincts or districts.
[t is clear that recent advances in digital photogrammetry have
accelerated the archiving and analysis of world heritage sites
(Chong et al., 2002). However, 3D modelling tools were not
completely successful to model the shape of the art works of
interest in cultural heritage applications. This is due to the high-
cost, and/or inaccurate imaging device and shape complexity
associated with artefacts to be modelled. Although, using metric
cameras result in accurate measurements, the disadvantage with
this class of camera remains to be the high cost. Therefore,
there is a desire to utilize cheaper image acquisition tools,
particularly amongst non-specialists, such as low-cost digital
cameras. Recent developments of digital cameras in terms of
high-quality/resolution and reduced costs have had a
considerable impact on the applications of photogrammetry and
in particular documentation of cultural monuments. Digital
cameras, intended to replace conventional film-based mapping
cameras, are becoming available along with many smaller
format digital cameras capable of precise measurement
applications. All such cameras require careful calibration to
determine their metric characteristics, which are essential to
carry out photogrammetric activities. Metric characteristics of
the camera, which are known as Interior Orientation Parameters
(IOP), include coordinates of the: principle point, camera
constant, radial and decentric lens distortion, are usually
determined through a camera calibration procedure. Different
calibration sessions can be used to check the stability of the
implemented camera, (Habib and Morgan; and 2003 Habib et
al., 2004).
Traditional camera calibration through bundle adjustment
requires a test field with numerous control points that have to be
precisely surveyed prior to the calibration process. Establishing
and maintaining such a test field is an expensive procedure that
has to be conducted by professionals. This paper introduces a
new approach for incorporating straight lines in a bundle
adjustment for calibrating off-the-shelf/low cost digital
cameras. Utilizing linear features is advantageous for various
reasons. First, straight lines can be easily established in the test
fields. Also, industrial scenes are rich with straight lines.
Moreover, image space linear features can be easily and
precisely extracted using image-processing techniques (Kubik,
1991). The most important advantage of straight lines is that
they
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