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Review

Close-range photogrammetry applicationsin bridge measurement: Literature review

Ruinian Jiang a,*, David V. Jauregui b, Kenneth R. White b

a New Mexico State University, Department of Engineering Technology and Surveying, EC III, Room 382, Box 30001,

MSC 3566, Las Cruces, NM 88003, United Statesb New Mexico State University, Department of Civil Engineering, Hernandez Hall, Box 30001, MS 3CE,

Las Cruces, NM 88003, United States

Received 24 August 2007; received in revised form 20 December 2007; accepted 27 December 2007Available online 9 January 2008

Abstract

Close-range photogrammetry has found many diverse applications in the fields of industry, biomechanics, chemistry, biol-ogy, archaeology, architecture, automotive, and aerospace, as well as accident reconstruction. Although close-range photo-grammetry has not been as popular in bridge engineering as in other fields, the investigations that have been conducteddemonstrate the potential of this technique. The availability of inexpensive, off-the-shelf digital cameras and soft-copy, pho-togrammetry software systems has made close-range photogrammetry much more feasible and affordable for bridge engi-neering applications. To increase awareness of the use of this powerful non-contact, non-destructive technique in thebridge engineering field, this paper presents a literature review on the basic development of close-range photogrammetryand briefly describes previous work related to bridge deformation and geometry measurement; structural test monitoring;and historic documentation. The major aspects of photogrammetry bridge measurement are covered starting from the late1970s and include a description of measurement types, cameras, targets, network control, and software. It is shown that earlyapplications featured the use of metric cameras (specially designed for photogrammetry purposes), diffuse targets (non-retro-reflective), stereoscopic photogrammetry network layout, and analog analytical tools, which transformed over time to the useof non-metric cameras, retro-reflective targets, highly convergent network layout, and digital computerized analytical tools.� 2008 Elsevier Ltd. All rights reserved.

Keywords: Close-range; Photogrammetry; Bridge; Deformation; Monitoring; Geometry

Contents

0

d

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8242. Development of close-range photogrammetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8243. Bridge deformation and geometry measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8254. Structural test monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 830

263-2241/$ - see front matter � 2008 Elsevier Ltd. All rights reserved.

oi:10.1016/j.measurement.2007.12.005

* Corresponding author. Tel.: +1 505 646 1506; fax: +1 505 646 6049.E-mail address: rjiang@nmsu.edu (R. Jiang).

824 R. Jiang et al. / Measurement 41 (2008) 823–834

5. Applications for historical bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8326. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833

1. Introduction

Photogrammetry is a technique for determiningthe three-dimensional geometry (location, size, andshape) of physical objects by measuring and analyz-ing their two-dimensional photographs. Generally,photogrammetry is divided into two categories: aer-ial and terrestrial photogrammetry. In aerial photo-grammetry, images are acquired via overhead shotsfrom an aircraft, providing topographic maps andland use details. In terrestrial photogrammetry (alsocalled non-topographic photogrammetry), imagesare acquired at locations near or on the surface ofthe earth and provide detailed dimensional informa-tion of an object. When the object size and the cam-era-to-object distance are both less than 100 m(330 ft), terrestrial photogrammetry is furtherdefined as close-range photogrammetry, anapproach where images are acquired around anobject with highly convergent camera orientations,generally pointing towards the center of the object[1]. Many successful and diverse applications ofclose-range photogrammetry can be found in thefields of industry, biomechanics, chemistry, biology,archaeology, architecture, automotive and aero-space engineering, as well as accident reconstruc-tion, to name a few [2–4]. Although close-rangephotogrammetry has not been as popular in bridgeengineering as in other fields, many pioneeringapplications in this field, as described in this paper,have illustrated the potential for growth. In addi-tion, the rapid development of digital imaging andcomputer technologies since the early 1990s hasmade close-range photogrammetry much more fea-sible and affordable for bridge engineering applica-tions. The availability of inexpensive, off-the-shelfdigital cameras and soft-copy, photogrammetrysoftware systems has made more bridge engineeringapplications of close-range photogrammetry a pos-sibility. To make engineers more aware of this pow-erful technique, this paper reviews the developmentof close-range photogrammetry and applications inbridge engineering including deformation andgeometry measurement; structural test monitoring;and historic documentation.

2. Development of close-range photogrammetry

The history of close-range photogrammetrycan be traced back to the late 1840s when the firstphotogrammetry system was developed by AimeLaussedat, a colonel in the French Army Corps ofEngineers. In 1849, Laussedat first utilized terrestrialphotographs to compile maps, and the approach wasofficially accepted by the Science Academy inMadrid in 1862. Laussedat later made a plan of Parisfrom photographs taken from building rooftops,which was exhibited at the Paris Exposition in1867. Due to his pioneering work, Laussedat iswidely recognized as the ‘‘father of photogramme-try” [5–7]. Another pioneer in the field of close-rangephotogrammetry is the Prussian architect, Mey-denbauer. He recorded many historical monuments,churches, and buildings with a close-range photo-grammetry method based on Laussedat’s techniques.In 1885, Meydenbauer established a state institute inBerlin to record architectural buildings [5].

The pioneering accomplishments of Laussedat,Meydenbauer, and many other photogrammetristsled to the formation of the International Societyfor Photogrammetry (ISP) in 1910, one of the mostimportant events in the history of photogrammetry[5,7]. The technical commissions of the societybegan work in specific areas of photogrammetry in1926, including aerial, terrestrial, architectural,and engineering photogrammetry [5]. Since then,close-range photogrammetry was considered abranch of terrestrial photogrammetry and was vir-tually ignored until the 1960s when photogramme-trists began to use inexpensive, non-customized(off-the-shelf) cameras for image collection. By the1970s, the use of close-range photogrammetry accel-erated due to the rapid development in computertechnology and expanded at even a faster rate inthe 1990s as the digital era emerged.

According to Gruen [8], the history of close-range photogrammetry can be divided into foureras. Era One extended from 1850 to 1984, andestablished the foundation of the technology byexploring basic systems. Theories developed duringthis period include image processing algorithms;

R. Jiang et al. / Measurement 41 (2008) 823–834 825

spatial network analysis methods; charge coupleddevices (CCD) for digital image recording; and leastsquares image matching methods. Era Two coveredthe years of 1984–1988, and focused on the develop-ment of early prototype systems including the cali-bration and application of CCD digital imagingsystems and high-speed data acquisition and pro-cessing methods. During this fast growing period,the name of ISP Commission V was changed to‘‘Close-Range Photogrammetry and MachineVision.” Era Three extended from 1988 to 1992,during which further acceptance and refinement ofclose-range photogrammetry occurred. Progress inthis period included fast growing and diversifiedapplications, and accelerated research and imple-mentation. While fully automated systems contin-ued to be explored, high accuracy close-rangephotogrammetric measurements in a wide range ofapplications had matured. Era Four (1992 – pres-ent) is a period in which digital close-range photo-grammetry has steadily developed. A goodexample of this progress is in the field of image sen-sors. During this period, high density, large format,and small pixel chips have become available and it isnow technically possible to manufacture a CCDchip containing 20,000 � 20,000 pixels with 5 lmpixel size. Off-the-shelf, consumer grade cameras,such as the Kodak Pro SLR model, now provide aresolution up to 14 million pixels at a relativelylow price [9,10]. In addition to image sensors, thecost of other components of photogrammetric sys-tems has also dropped significantly; as a result, abroader range of applications have become afford-able for engineering purposes. Other advances inthis period include the development of fully digi-tized systems; automated data acquisition and pro-cessing via machine vision systems; and quick andclear data interpretation.

As a summary of the application of close-rangephotogrammetry in the field of structural engineer-ing, Mills and Barber [11] reviewed the state-of-the-art of the technique in this field and observedthe following:

� improved photogrammetry network design suchas multi-station convergent networks providesbetter accuracy, precision, and reliability;� camera self-calibration and analytical processing

techniques allow the use of non-metric camerasand a simplified camera calibration process;� more low cost software packages are available to

users;

� development of internet technology has made on-line photogrammetric measurements possible;� advances in digital techniques have eliminated

the inconvenient image digitalization process,and have provided users a complete digital work-flow; and� modern digital cameras and better analytical

tools provide more flexibility and improved effi-ciency for photogrammetric measurements.

Jauregui and White [12] summarized basic ele-ments and system requirements for bridge engineer-ing applications of close-range photogrammetry.For a typical bridge measurement project, the basicinstruments include an off-the-shelf, medium to highresolution digital camera (such as Kodak DCS andPro SLR series); 2–4 scale bars (to establish networkcontrol); uniformly distributed artificial and/or nat-ural targets (more targets are preferable for highermeasurement accuracy); photogrammetry software(such as PhotoModeler and Australis); and a totalstation for control point measurement. Flash pho-tography and retro-reflective targets are generallyused for high-accuracy measurement.

It can be concluded that after more than onehundred and fifty years of development, close-rangephotogrammetry has now entered a fully digitizedera where its uses are rapidly expanding. This tech-nology possesses great potential in bridge engineer-ing and it is being applied to an ever increasingrange of tasks which are reflected by the examplesgiven in the following sections.

3. Bridge deformation and geometry measurement

The major aspects of bridge measurement appli-cations are summarized in Table 1 which includestypes of measurement, cameras, targets, networkcontrol, and software, covering the years from1985 to 2003.

The early applications in this field featured the useof metric cameras (specially designed for photo-grammetry purposes), diffuse targets (non-retrore-flective), stereoscopic photogrammetry networklayout, and analog analytical tools, which trans-formed over time to the use of non-metric cameras,retro-reflective targets, highly convergent networklayout, and digital computerized analytical tools.The applications given in Table 1 are reviewed inorder of date performed in the following paragraphs.

In 1985 the Virginia Highway and TransportationResearch Council sponsored a project on photo-

Table 1Application for bridge deformation and geometry measurements

Researcher Test object Type ofmeasurement

Target and type ofphotography

Camera used Network control Software used

Bales (1985) Reinforcedconcretedeck

Crack length andwidth

Diffuse targets,non-flashphotography

Zeiss UMK 10/1318,metric film camera(100 mm lens)

Control pointsurvey

Stereoscopiccomparator

Bales and Hilton(1985)

Steel I –beam

Vertical deflection

Steel girderbridge

Thermal and deadload deflection

Kim (1989) Highwaybridge

Long-termdeformationmonitoring

Diffuse targets, non-flash photography

Metric film camera(150 mm lens)

Control pointsurvey

Self-developed

Abdel-Sayedet al. (1990)

Soil-steelbridge

Geometry,deformation

Retro-reflectivetargets, flashphotography

Leica film camera(24 mm lens)

Scale bars Elcovision 10

Cooper andRobson(1990)

Steel bridge Deformation Retro-reflectivetargets, flashphotography

Zeiss UMK 10/1318metric film camera(100 mm lens)

Control points Intermapanalyticalcomparator

Forno et al.(1991)

Arch bridge Deformation Retro-reflectivetargets, flashphotography

Zeiss UMK-10 N metriccamera (2.1 m lens)

Control points Microscope

Albert et al.(2002)

Reinforcedconcretebeam

Vertical deflection Diffuse targets, non-flash photography

Kodak DCS660 digitalcamera, machine visioncamera (24 mm lens)

Distancemeasurementbetween targets

Ellipseoperator

Concretearch bridge

Leitch (2002)Jauregui et al.(2003)

Steel beam Vertical deflection Diffuse targets, non-flash photography

Kodak DCS660 digitalcamera (28 mm lens)

Control pointsurvey

FotoGP/C girderbridge

Girder camber anddead loaddeflection

Steel girderbridge

Live loaddeflection

Norris (2003)Johnson(2001)

Suspensionbridge

Geometry Retro-reflectivetargets, flashphotography

Imetric and KodakDCS660 digital cameras

Control pointsurvey

Imetric

826 R. Jiang et al. / Measurement 41 (2008) 823–834

grammetric bridge evaluation including a conditionsurvey and vertical deflection measurement [13,14].In the first study of the project, close-range photo-grammetry was applied to evaluate bridge condition,in particular, delaminations in a reinforced concretebridge deck; both the length and width of cracks wererecorded. In the second study, the vertical deflectionof a steel I-beam was measured both by photogram-metry and dial gages and the average differencebetween the two measurements was found to be1.0 mm (0.040 in.). In the third study, the thermaland dead load deflections of the steel girders of a lightrail bridge were measured. The bridge was a 3-spancontinuous structure with a total length of 139 m(464 ft); the length of the center span measured was51 m (170 ft). The camera was positioned at threelocations under mid-span facing up at a distance ofabout 10.8 m (36 ft) from the bottom of the girders.

The average difference between photogrammetrymeasurements and level readings was approximately3 mm (0.12 in.), with a maximum value of about9 mm (0.36 in.).

Kim [15] performed a long-term deformationmonitoring of a 526 m (1727 ft) long Wisconsin statehighway bridge via photogrammetry (see Fig. 1). Theproject utilized a camera with a 150 mm (6 in.) lens,and the distance separating the bridge and the cam-era was 122 m (400 ft). Images were recorded on con-ventional 230 � 230 mm (9 � 9 in.) film and wereanalyzed using a program developed specifically forthe project. All the control points were set on thenorth end of the bridge due to field conditions andas a result, the measurement accuracy worsenedmoving from north to south. It was concluded thatthe precision of the deformation measurement viaphotogrammetry was within ±14 mm (0.6 in.) in

Fig. 1. Camera stations and orientation [15].

R. Jiang et al. / Measurement 41 (2008) 823–834 827

the length and height directions, and ±30 mm(1.2 in.) in the width direction, with a 95% confidencelevel.

Abdel-Sayed et al. [16] reported the use of close-range photogrammetry for the deformation moni-toring of soil-steel bridges. The main objectives ofthe monitoring program were to determine thecross-sectional shape of the metal conduit at certainlocations and to assess the deformations throughperiodic monitoring. Targets were 6 mm (0.25 in.)

Additional targets on bolts at longitudinal seams

Four or more targets are recommended for each multi-plate section above waterline or debris

Longitudinalseamscontinuous or staggered

Targets

a b

Fig. 2. Soil bridge measurement: (a) targe

diameter retro-reflective circles, which were evenlydistributed along the cross section (see Fig. 2a).Scale rods were used consisting of retro-reflectivetargets on aluminum angles, which were placed indifferent directions in the object space to provideuniform object scale in all directions. Photographswere taken using a 24 mm (0.94 in.) wide-angle lenscamera along the conduit at two locations for eachsection (see Fig. 2b). The accuracy was evaluated bycomparing the distances between points calculated

Optical axes are convergent for two camera positions

Targeted cross section

Soil-steelstructure in plan

Camera

t layout; (b) camera placement [16].

ObjectObject Plane

XY

Image Plane x yProjection Center Δ Δ

ΔΔ

Fig. 4. Single-camera deformation measurement [19].

828 R. Jiang et al. / Measurement 41 (2008) 823–834

by photogrammetry and obtained by direct mea-surements. For a structure having a span of approx-imately 4 m (12 ft), the mean difference of distancesranged from 2 to 7 mm (0.080 to 0.276 in.) for cross-sections having the scaling devices, and from 30 to80 mm (1.18–3.15 in.) for cross-sections withoutthe scaling devices. The mean difference of distancesin the longitudinal direction ranged from 20 to40 mm (0.787–1.575 in.).

The City University of London monitored thedeformation of a military steel bridge [17]. The mea-surements focused on an 18 m (59 ft) bridge sectionusing seven camera stations, as shown in Fig. 3. Atotal of 768 measurements of target coordinateswere made, the maximum standard deviations ofwhich were found to be ±0.39 mm (0.015 in.),±0.62 mm (0.024 in.), and ±0.23 mm (0.009 in.) inthe x, y, and z direction (see Fig. 3), respectively.

Forno et al. [18] reported the studies performed atthe University of Dundee in Scotland on the defor-mation measurement of a decommissioned masonryarch bridge and a full-scale laboratory model of thebridge. The bridge had a single closed-spandrel archwith a 4 m (13.2 ft) diameter and overall dimensionsof 6 m � 4 m � 6 m (20 ft � 13 ft � 20 ft, length �height � width). The bridge was tested under a con-centrated load applied at the top of the spandrel.Both Moire photography and close-range photo-grammetry were applied to measure the deformationof the bridge. Moire photography results providedcontrol for the photogrammetric measurements sincescale bars appeared too dark in the photos to serve asan accurate reference. The standard deviation of thephotogrammetric measurement was approximately0.2 mm or 0.008 in.

Bauhaus University and Dresden University ofTechnology (both in Germany) performed studies

Bridge

Y (m)

2 4 6 8 10-4

-2

0

2

4

6

Fig. 3. Layout of the cam

on the deformation measurement of a laboratorybeam and a field bridge using a single camera setup[19]. The basic principle employed is shown inFig. 4; that is, if the camera image and the objectplanes are parallel, the actual dimension of anobject will be directly proportional to that measuredin the image. Given the deformation in the imageplane (Dx and Dy), the deformation of the actualobject (DX and DY) can be calculated by the follow-ing equations:

DX ¼ b � Dx; DY ¼ b � Dy

where b is the scale factor which can be determinedvia control points or scale bars.

In the laboratory study, the deflection of a 2 m(6.6 ft) concrete beam was measured. Nine retro-reflective circular targets with a diameter of 14 mm(0.55 in.) were placed towards the bottom of thebeam for measuring the deflection at those locations(see Fig. 5a). Natural targets, such as naturalpatches on concrete surfaces, were also identifiedin order to evaluate the accuracy of such targets.Conventional displacement sensors were placed atthree locations to check the photogrammetric mea-surements. A measurement precision of approxi-mately 0.01 mm (0.0004 in.) was achieved with a

Pin Joint

X (m) 12 14 16 18

era positions [17].

Fig. 5. Photogrammetry deflection measurement: (a) beam; (b) field bridge [19].

R. Jiang et al. / Measurement 41 (2008) 823–834 829

Kodak DCS660 camera and 0.04 mm (0.0016 in.)with a machine vision camera. The largest differencefound between the photogrammetric and the dis-placement sensor measurements was approximately0.1 mm (0.004 in.). In the field study, the verticaldeflection of an unreinforced concrete arch bridgelocated in Erfurt, Germany was measured. Thebridge was built in 1900 and has a single span,27 m (89 ft) long and 12.5 m (41 ft) wide (seeFig. 5b). In order to verify the restoration plan ofthe bridge, a load test was performed to determineits safe load capacity and close-range photogram-metry was chosen to measure the deformation ofthe bridge under the applied load. A 1300 � 1030pixel machine vision camera was placed on the westbank of the river, approximately 32 m (105 ft) fromthe bridge. This distance provided a horizontal fieldof view of 32.5 m (107 ft), so a single image couldcover the whole bridge. Fig. 5b shows a sampleimage of the arch bridge taken by the machinevision camera. The vertical deformation was visual-ized online in time-deflection diagrams. Nine induc-

tive length gages were placed on a trestle installedunderneath the bridge to check the photogrammet-ric measurements. The photogrammetric targetswere 100 mm (3.94 in.) diameter white circles placedon a black background. The maximum verticaldeflection of the bridge measured was approxi-mately 2 mm (0.079 in.), and a standard deviationof 0.1–0.2 mm (0.004–0.008 in.) was found betweenthe photogrammetric and gage measurements.

New Mexico State University (NMSU) conducteda comprehensive study on bridge deflection measure-ment using close-range photogrammetry [20,21].Studies were performed on a laboratory steel beamand on two field bridges. The first bridge tested wasa single-span, prestressed concrete bridge; the secondwas a 7-span, simple-supported steel girder bridge.

In the laboratory study, a 12.2 m (40 ft) longW21 � 62 steel beam was loaded at mid-span by aconcentrated load in weak axis bending. Twenty-one double-sided targets were evenly placed on thetop of the beam. Images were acquired aroundthe beam and deflections measured by close-range

830 R. Jiang et al. / Measurement 41 (2008) 823–834

photogrammetry were compared with those readfrom dial gages; differences in the measurementsranged from 0.51 mm (0.02 in.) to 1.27 mm (0.05 in.).

In the first field test, the girder camber of a pre-stressed concrete bridge located in Las Cruces, NewMexico was measured, including the initial camberof the girders before loading and the final camberafter placement of the reinforced concrete deck slaband traffic barriers. The bridge has a single 32.2 m(105 ft) long, 18� skewed span with five prestressedBT-1600 bulb-tee girders. A total of fourteen controltargets were placed on the abutments and retainingwalls at both ends of the bridge. Photos were takenfrom the east side of the bridge and also underneaththe girders; the average camera-to-object distancewas about 18.3 m (60 ft). Photogrammetric measure-ments of the initial camber were compared with levelrod readings; the maximum deviation of the twomeasurements was within ±17 mm (0.67 in.) for fourof the girders, and 28 mm (1.1 in.) for the remaininggirder. The maximum initial camber occurred at themid-span of girder 2 with a value of about 140 mm(5.5 in.). Dead load deflections under the deck andbarrier weight measured by photogrammetry werethen compared with the design estimates (i.e., thedead load deflection diagram); the differences variedfrom 2.9 mm (0.11 in.) to 5.4 mm (0.21 in.) for all thegirders. The maximum dead load deflection turnedout to be approximately �35 mm (�1.38 in.). Forthe final girder camber, a comparison was made withtotal station measurements. For the 15 girder loca-tions, the average absolute difference was 2.95 mm(0.116 in.), with a range between �6.40 mm(0.252 in.) and +4.27 mm (0.168 in.).

The second field test study was conducted on anon-composite, steel girder bridge built in 1937and located in the vicinity of Truth or Conse-quences, New Mexico. The bridge has seven sim-ple-supported spans, one of which was testedunder truck loading. The tested span consisted ofsix 14.9 m (49 ft) long CB30 � 116 girders (similarto a W30 � 116). Double-sided photogrammetrictargets were used both for control and tie purposes.The photogrammetric measurement results werecompared to those obtained from finite elementanalysis, level rod readings, and curvature-basedmeasurements derived from strain gages. With amaximum deflection of about 8 mm (0.31 in.), thedifferences in deflection measurements from photo-grammetry, curvature, and the level rod were within0.5–1.5 mm (0.02–0.06 in.) for all girders at mid-span.

Sewall Company applied digital close-range pho-togrammetry to measure the geometry of the 622 m(2040 ft) long Waldo-Hancock Cable SuspensionBridge between Prospect and Verona, Maine [22].The bridge was built in 1931 and had shown seriousdeterioration both in its superstructure and deck[23]. The bridge dimensions measured by photo-grammetry were used in the rehabilitation planningof the bridge. Control points were placed at theapproaches to the bridge and surveyed using a totalstation, along with real-time kinematic (RTK) GPSmethods. Images were acquired from a helicopter.From photogrammetric analysis, Sewall providedinformation on bridge and cable geometry for fur-ther structural analysis. The measurements includedthe elevation and offset of cables, trusses, piers, themain tower, and cable bents. The accuracy of mea-surement for critical dimensions of the bridge wascomparable to that of a conventional survey. Thestandard deviation of the photogrammetric mea-surements was 3 mm (0.12 in.) over a length of213 m (700 ft) of a bridge section, and 15.9 mm(0.625 in.) over the total length of the bridge [23].Compared to traditional surveying methods, close-range photogrammetry proved to be more efficient.Measurements accomplished in less than three daysin the field would have taken 10 days for a conven-tional survey, and images were acquired withoutphysically accessing each measurement point. Thewhole process was non-intrusive, and only createdminimal impact on traffic flow.

It is observed from the above examples thatclose-range photogrammetry provides a very conve-nient way for bridge deformation monitoring andgeometry measurement. The accuracy of close-rangephotogrammetry is sufficient for most bridge engi-neering applications and the implementation mayprove to be easier and more cost-effective comparedto traditional methods.

4. Structural test monitoring

Frequently, components of a bridge are testedinstead of the whole bridge due to the limitationsof cost, time, and other experimental constraints.There have been many tests conducted on bridgeelements such as beams and columns where photo-grammetry was used to monitor deformation, afew examples of which are given in this section.

Scott [24] performed a study on photogrammet-ric deflection monitoring of a multiple box, curvedgirder bridge to detect the buckling load of the

R. Jiang et al. / Measurement 41 (2008) 823–834 831

compression flange and to explore the ultimate fail-ure mechanism of the model bridge. Photos werecaptured at 27 camera stations along both sides ofthe bridge. A total of about 4000 targets were placedon the bottom flange, and 1800 images were used inthe image processing with an analog stereoscope.Compared to dial gage results, an accuracy of±0.2 mm (±0.008 in.) was achieved by the photo-grammetric deflection measurement.

Woodhouse et al. [25] conducted several highstrength, concrete column tests. The aim of the testswas to determine the influence of steel hoop rein-forcement on the failure of the columns. Columndeflection was monitored during the tests by close-range photogrammetry. Linear variable displace-ment transducers (LVDT) were used to measuredeformation of the column for comparison. Fourdigital cameras were used, two of which had a reso-lution of 1534 � 1024 pixels and the other two,1008 � 1018 pixels. A vision metrology system wasused which was controlled remotely in such a waythat images were captured automatically and syn-chronously by the four cameras.

Fraser and Riedel [26] performed a study on themonitoring of thermal deformations of steel beams.The temperature variation of the steel beams rangedfrom 1100 �C down to 50 �C, and the measurementrate was one set every 15 s. In order to collectapproximately 70–80 sets of measurements in about2 h, a highly automated, on-line data processing sys-tem was used. Two groups of targets were utilized.Group 1 had about 10 to 15 targets, and was usedto monitor the deformation of the beam; group 2had about 30 targets that were placed on the wallbehind the beams and stayed stationary during theentire test, serving as reference points. The average

Fig. 6. Bridge beam test: (a) network la

camera-to-object distance for the outer cameraswas 9.6 m (31.7 ft), and 6.7 m (22.1 ft) for the centercamera. An Australis� system was used for the off-line photogrammetric analysis, which was modifiedfor the on-line process of real time measurement.The coordinate changes of the targets on the steelbeam were recorded continuously over time. Thefinal RMS value of coordinate residuals in approx-imately 800 point measurements averaged 1.6 lm(close to 0.2 pixels), which yielded an accuracy inthe object space of 0.7–1.3 mm (0.03–0.05 in.).

The Civil Engineering Department at Curtin Uni-versity of Technology in Australia performed a seriesof laboratory studies on concrete beam deformationmeasurement [27]. The beams were taken from a dis-mantled bridge in Western Australia, and includedinverted U-shaped reinforced concrete and rectangu-lar prestressed concrete beams. The beams were sim-ple-supported at both ends, and destructive loadingtests were performed to evaluate their ultimatestrength. The layout of the test is shown in Fig. 6a.Two 8 mm-lens video cameras were placed at twolocations with a convergence angle of about 47�(see Fig. 6a), with an image size of 768 � 574 pixels.The two cameras remained stationary throughoutthe test and were self-calibrated using the test images.The photogrammetry analytical software Australis(Version 5.02) was used for both camera self-calibra-tion and target coordinate calculations. Load-deflec-tion diagrams were obtained for three prestressedconcrete beams, as shown in Fig. 6b.

The deflection measured with LVDTs was usedto check those obtained by photogrammetry. Theauthors stated that an obvious disadvantage of con-ventional instruments such as LVDTs is its limitedmeasurement range of only 25 mm or 0.98 in. (the

yout; (b) load vs. deflection [27].

832 R. Jiang et al. / Measurement 41 (2008) 823–834

elastic range); beyond this range, the measurementaccuracy drops quickly. In contrast, close-rangephotogrammetry provided measurements over theentire deformation range (see Fig. 6b). Another dif-ference between traditional gages and photogram-metry is that the latter can measure 3-dimensionaldisplacement, while the former measures deflectionin only one direction. Shear strength tests were alsoperformed on the inverted U-shaped fiber-rein-forced concrete beams. Load-deflection diagramsand 3D displacement profiles were also obtainedfor these U-shaped beams. The mean measurementprecision obtained by photogrammetry determinedfrom 25 group point coordinates was ±0.27,±0.54, and ±0.24 in the x, y, and z direction (seeFig. 6a), respectively. A curb section inverted U-shaped beam with an asymmetric cross-sectionwas also tested; the torsion of the beam wasrecorded by photogrammetry. Close-range photo-grammetry was found to provide an effective wayto measure torsional displacements that are other-wise very difficult to measure conventionally.

Hegger et al. [28] reported a test on pre- andpost-cracking shear behavior of prestressed concretebeams using laser-interferometry and close-rangephotogrammetry. Laser-interferometry was used tomeasure the pre-cracking behavior, while close-range photogrammetry was applied to measure thepost-cracking shear behavior. The beam web wasmarked with black measuring dots at a spacing of25 mm (0.98 in.) for photogrammetry measurement.Photos were taken at nine stations from two eleva-tions around the marked area for each loading step.Calibrated rods were placed at the top and bottomof the beam for setting scale. The accuracy of the3D coordinates of the measured points was0.02 mm (0.0008 in.), which accurately determinedthe crack locations and openings. From the mea-surement of cracks and monitoring their develop-ment, the shear transferred across the cracks byshear friction was estimated.

5. Applications for historical bridges

This section reviews applications of close-rangephotogrammetry for historic bridge restorationand monitoring. Examples of architectural photo-grammetry that focus on historic building documen-tations are not included here. The reader is referredto Dallas [4] for that information.

Spero [29] conducted a study on the applicabilityand accuracy of close-range photogrammetry in the

documentation of historic bridges and other trans-portation structures. Different structure types suchas concrete arches, steel trusses, and brick and woodbeams were chosen for documentation, and a widerange of field conditions were selected to test thefeasibility of close-range photogrammetry. A ZeissUMK 10/1318 metric camera with a focal lengthof 99 mm (3.90 in.) was used to acquire images. Tar-gets were installed around the object and the dis-tances between targets were hand measured to setup the reference. In addition to the creation ofdrawings, the potential of photogrammetry for themeasurement of cross-sectional areas and the thick-ness of structural members was also explored andchecked with hand measurements. The differencesbetween photogrammetry and hand measurementwere found to be very small. In one example, the dif-ference for 18 point measurements was less than3.18 mm (1/8 in.).

Shigenori et al. [30] reported a project in whichphotogrammetric information and geographicinformation system (GIS) models were used todevelop an integrated design and management sys-tem for a historical bridge restoration in Japan.The bridge (designated the Nishida Bridge) had fourarch spans, and was made of natural stone blocks.The integrated system consisted of photogramme-try, coordinate management, photograph manage-ment, and 3D visualization sub-systems. A modelof the bridge was established from old photos takenin the 1870s using single photograph analytical tech-niques, and verified in the field. The arc shape of thebridge (160 m or 528 ft long) was calculated bydividing the entire arc into 88 elements. A multi-window system was applied to transform photo-graphs into AutoCAD� drawings; by moving acursor to a calculated point on an old photographin one computer screen, the analytical result couldbe verified easily in the AutoCAD� drawing dis-played in another monitor. A total of 31 points weremeasured on the bridge surface photogrammetrical-ly, and the radius of arcs and co-ordinates of thesepoints were calculated. Photogrammetry was alsoused to exhibit bridge information on material andmechanics properties, construction technology, res-toration design, bridge history, and restoration con-struction documentation.

6. Conclusions

Close-range photogrammetry is a technique thathas many unique advantages, a few of which are

R. Jiang et al. / Measurement 41 (2008) 823–834 833

(1) it is a non-contact technique that is capable ofmeasuring difficult-to-access structures; (2) it is lesslabor-intensive; (3) it records a large amount of geo-metric information in a short time period by acquir-ing images; (4) it allows revisiting the visual recordsand performing additional analysis at a later time;and (5) it can be used as a convenient tool for routinemeasurement applications. With the rapid develop-ment of computer technology and digitized imagerecording and processing systems, close-range pho-togrammetry has entered a fully digitalized era withgreat potential for bridge engineering applications.There have been several successful examples in thefield of bridge deformation measurement and moni-toring, most of which reached an order of accuracyof about 1 mm (0.04 in.). For bridge geometry mea-surement, the field work has been found to bereduced by more than 50% while maintaining thesame level of accuracy compared to conventionalsurveying methods. Close-range photogrammetryhas been found very useful in test monitoring dueto its capability of measuring 3D deformation andbehavior up to the failure of bridge elements, whichmake it very useful in torsion, shear, axial, and bend-ing experiments. Close-range photogrammetry hasalso been found in historic bridge documentationand rehabilitation. It is concluded that close-rangephotogrammetry is a powerful measurement tech-nique that can provide unique solutions for broadand diverse bridge engineering applications.

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