The Use of Surface Model in Area-Based 
Matching in Determining Deformations of Steel Structures 
Mushaitry MUSTAFFAR * * Anuar AHMAD °, Ahmad Yusof SHAHDAN * 
2 Faculty of Civil Eng., Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia. 
b Faculty of Geoinformation & Eng. Sc., Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia. 
* Corresponding author (mushairry(@fka.utm.my ; mushairry@hotmail.com) 
  
Commision III, WG 1111/8 
KEY WORDS : Photogrammetry, Engineering, Matching, Reconstruction, Close-Range, Digital 
ABSTRACT 
In civil engineering, surface deformations of a structure, in particular steel, are useful indicators pertaining to its failure. 
Present laboratory methods employed in determining the deformations are through the use of transducers and strain gauges. 
As such, much time is spent in the preparation of the equipment and peripherals for a particular test. Furthermore, surface 
deformations can only be measured at points where gauges are fixed and in many cases would not cover the entire surface. 
This paper presents the use of close range digital photogrammetry to obtain a three-dimensional model of a structure's 
surface. Since, photogrammetry has always had the advantage of being able to provide measurements on a large number of 
points on the object of interest, the representation of the surface deformations would be better. Image correspondence is 
achieved by using an area-based image matching which makes use of simple surface models. Laboratory tests involving load 
test on steel I-beams were performed. Images of the steel beam under various load were captured using off-the shelf digital 
cameras that are relatively fixed and calibrated. Whilst the image matching process employs a revised area-based matching 
algorithm, the image coordinate refinements and the three-dimensional model of the beam’s surface was acquired through 
elementary photogrammetric operations. Validation of the results was done by means of comparing the photogrammetric 
output against those obtained from the transducers and gauges. Initial results show that the differences between the 
photogrammetric and conventional approaches are not statistically significant. This indicates that the use of close-range 
digital photogrammetry in producing the surface deformations is a viable additional approach in determining the physical 
properties of steel structures. 
1. INTRODUCTION object of interest, which has usually been earth's 
topography. A once laborious exercise, if performed 
Steel structures, such as bridges, consisting of steel using conventional methods, can now be automated using 
girders and decks, are designed optimumly with the digital images together with appropriate image 
intention of making full use of its mechanical properties. manipulation algorithms. 
In order to guarantee safety, testing of steel beams and 
columns in terms of their distortions and deformations is In the case of aerial survey, “digital photogrammetric 
salient to the structural engineers in determining the work-stations”, which are, in effect, standard work- 
optimum design of steel structures. Furthermore, with stations operating extensive and sophisticated 
the intention of a better understanding and an accurate photogrammetric software, available from a small 
numerical modelling of the steel structures, number of manufacturers, are able to carry out relative 
measurements, in particular the deformation, are orientations and digital terrain model generation with 
indispensable. Present approach in measuring distortions complete automation given digitised photographs of 
makes use of suitably located electronic transducers or terrain meeting certain reasonable criteria for terrain 
gauges to obtain the magnitude of displacements. The undulation and radiometric texture. With assistance from 
shape of the deformed surface is normally measured the digital terrain models (DTM), orthoimages and 
manually by hand at points of interest which are contours can be automatically and quickly generated. 
normally the nodes of a grid drawn on the steel surface. Interior orientation and absolute orientation are partially 
Such method, apart from being crude, is tedious and less automated. Generation of a DTM of satisfactory density 
accurate. A more practical approach to alleviate this and accuracy from a suitable pair of aerial photographs 
problem is by using close-range digital photogrammetry can be achieved at rates of order of 25 points per second. 
technique. This is achieved through computer programs to carry out 
the equivalent of placing the “floating mark” on the 
surface, as operators need to do on analogue and 
2. DIGITAL PHOTOGRAMMETRIC analytical photogrammetric plotters 
MEASUREMENT 
In non-topographic measurement, automation of 
Photogrammetry has always had the advantage of being measurement of those objects which have been marked 
able to measure an immense number of points on the with appropriate types of targets is now a highly 
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