Use of Laser Scanning 

Technology to Obtain 

As-Built Records 

of Historic Covered 

Bridges 

Robert J. Ross

Brian K. Brashaw

Samuel J. Anderson

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Paper

FPL–RP–669

In cooperation 

with the

United States

Department of

Transportation

Federal 

Highway 

Administration
August 2012

Ross, Robert J.; Brashaw, Brian K.; Anderson, Samuel J. 2012. Use of laser 

scanning technology to obtain as-built records of historic covered bridges. 

Research Paper FPL-RP-669. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 18 p.

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Abstract

Covered bridges are part of the fabric of American history. 

Although much effort is expended to preserve these structures, many are lost forever. The National Park Service’s 

Historic American Engineering Record (HAER) has efforts 

under way to document historic structures. Their Level I 

documentation is defined in the Secretary of the Interior’s 

Standards and Guidelines for Architectural and Engineering 

Documentation and consists of measured and interpretive 

drawings, large-format photographs, and written historical 

reports. To assist in this effort, newer technologies need to 

be explored that can provide as-built records at a faster rate 

and with more accuracy.

The University of Minnesota Duluth’s Natural Resources 

Research Institute (UMD NRRI), in cooperation with the 

USDA Forest Products Laboratory and Federal Highway 

Administration, conducted a study to examine the use of 

laser scanning technologies for providing as-built records 

for historic covered timber bridges. Additional support for 

the study was provided by the City of Zumbrota, Minnesota, 

via funds from the Operational Research Program (OPERA) 

of the Minnesota Local Road Research Board. This research 

report summarizes results obtained from that study.

Keywords: Covered timber bridges, laser, scanning, historic 

records

Contents

Introduction..........................................................................1

Literature Review.................................................................1

Methods................................................................................1

 Selection of Bridges.........................................................1

 Three-Dimensional Laser Scanning and 

 Data Processing................................................................2

Results..................................................................................3

 Laser Scanning.................................................................3

 Rapid Prototype Development.........................................4

 Comparison of Laser Scanning Equipment Results 

 with Field Measurements.................................................4

Summary and Conclusions ..................................................6

References............................................................................7

Figures.................................................................................8

This study is part of the Research, Technology and 

Education portion of the National Historic Covered 

Bridge Preservation (NHCBP) Program administered 

by the Federal Highway Administration. The NHCBP 

program includes preservation, rehabilitation and restoration of covered bridges that are listed or are eligible 

for listing on the National Register of Historic Places; 

research for better means of restoring, and protecting 

these bridges; development of educational aids; and 

technology transfer to disseminate information on covered bridges in order to preserve the Nation’s cultural 

heritage.

This study is conducted under a joint agreement between the Federal Highway Administration–Turner 

Fairbank Highway Research Center, and the Forest 

Service – Forest Products Laboratory.

Federal Highway Administration Program Manager– 

Sheila Rimal Duwadi, P.E.

Forest Products Laboratory Program Manager– 

Michael A. Ritter, P.E.

Conversion Table

English unit Conversion factor SI unit

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)
Use of Laser Scanning Technology to 

Obtain As-Built Records of Historic 

Covered Bridges

Robert J. Ross, Supervisory Research General Engineer

Forest Products Laboratory, Madison, Wisconsin

Brian K. Brashaw, Program Director, 

Samuel J. Anderson, Engineer, 

University of Minnesota Duluth, Natural Resources Research Institute

Introduction

Covered bridges are part of the fabric of American history, 

and several hundred historic covered bridges still exist today. Although much effort is expended to preserve these 

structures, the high cost of restoration, neglect, vandalism, 

and arson often take their toll. Many are lost forever. One 

of the more famous bridges from The Bridges of Madison 

County movie fame was burned in 2003, and Hurricane 

Irene destroyed a number of New England bridges in 2011. 

Because we cannot completely prevent these types of incidents from occurring, the National Park Service’s Historic 

American Engineering Record (HAER) has efforts under 

way to document historic structures. Their Level I documentation is defined in the Secretary of the Interior’s Standards 

and Guidelines for Architectural and Engineering Documentation. It consists of measured and interpretive drawings, 

large-format photographs, and written historical reports. To 

assist in this effort, newer technologies need to be explored 

that can provide as-built records at a fast rate and with 

greater accuracy.

The demonstration study summarized in this report was 

conducted to examine the technical feasibility of using laser scanning technologies for obtaining as-built records for 

historic covered timber bridges. A secondary objective was 

to identify other applications of this technology, notably for 

other transportation structures.

Literature Review

Three-dimensional (3D) laser scanners are instruments that 

record precise and accurate surface data of objects in a nondestructive manner. These instruments use an infrared beam 

of light to calculate and record the distance to an object, 

typically as data points with spatial coordinates. These data 

are then analyzed using various types of computer software 

to generate a detailed image of coordinates and dimensions. 

Three-dimensional laser scanners have successfully been 

used to digitize objects of various sizes ranging from small 

diagnostic artifacts to large, complex sites of monumental 

architecture (FARO Technologies 2011a, b).

A wide number of companies manufacture various types 

of 3D laser scanners. Generally, these units use light detection and ranging technology (LiDAR), where laser pulses 

determine the distance to an object or surface. The distance 

to an object is determined by using time-of-flight between 

transmission of a pulse and detection of the reflected signal. 

A point cloud of data is then collected and can be converted 

into the true shape of the object.

The units used in this project, a FARO LS 880 model and a 

Photon 120 model (FARO Technologies, Lake Mary, Florida), used similar technology to acquire the scan points. A 

laser beam is emitted from a rotating mirror out toward the 

area being scanned. The laser beam is then reflected back to 

the scanner by objects in its path. The distance to the objects 

defining an area is calculated, as well as their relative vertical and horizontal angles (FARO Technologies 2011a, b).

Several bridge projects were noted in the literature review. 

The Pennsylvania Department of Transportation (PennDOT) 

completed an initial study in 1999. In this study, the goals 

were to evaluate the technology for creating as-built drawings. A comparison of traditional and 3D scanning estimated 

an overall time savings of 100+ person-hours through the 

use of 3D scanning (Foltz 2000). Based on this assessment, 

PennDOT purchased two laser scanners in 2000. A second 

assessment was completed by Jaselskis and others in 2003, 

showing that laser scanning could be used cost effectively 

for preliminary surveys to develop triangular network (TIN) 

meshes of roadway surfaces and to measure bridge beam 

camber more safely and quickly compared with conventional approaches. Other applications noted in this publication 

showed potential applications for laser scanning to include 

developing as-built drawings of historical structures such as 

the bridges of Madison County.

Methods

Selection of Bridges

The bridges for scanning and assessment used in this study 

are located in Wisconsin, Iowa, and Minnesota. Key background information (Table 1), detailed descriptions, and 

photographs are summarized in the following paragraphs. 

Contact was made with the appropriate government or 

administrative staff for each bridge, and permission was 

also secured to obtain scans. Note that four of the bridges 

scanned included the historic Madison County, Iowa, 

bridges.
Research Paper FPL–RP–669

2

Cedarburg, Wisconsin, Covered Bridge

The last remaining historic covered bridge in Wisconsin, 

the “Red Bridge,” was built in 1876. It is located just outside the city of Cedarburg, Wisconsin, in Ozaukee County 

(Figs. 1, 2). According to Ozaukee County records (2011),

Built in 1876, the original span measured 120’ long 

and 12’ wide. Its construction was of a certain type 

of pine found near Baraboo, Wisconsin. All of the 

timber and planks were cut and squared in a mill 

near that city. The lumber was then hauled to the 

proposed site on Cedar Creek where all pieces were 

fitted and set in place. The type of construction is 

known as lattice truss with interlacing 3 × 10 inch 

planks all held together by 2 inch hardwood pins 

and floored with three inch planking. In 1927, a 

center abutment was placed to carry the heavier 

traffic of automobiles and trucks. (Ozaukee County 

2011)

Madison County, Iowa Covered Bridges

The bridges in Madison County, Iowa, are world famous, 

and they are excellent examples of the construction of covered bridges in the 1870–1880s. As noted in 2011 on the 

Madison County, Iowa, website,

Our historic, world-famous covered bridges were 

popularized by Robert James Waller’s novel, The 

Bridges of Madison County, and the feature film 

starring Meryl Streep and Clint Eastwood. Five 

of the original covered bridges remain, all listed 

on the National Register of Historic Places. The 

bridges were covered by order of the County Board 

of Supervisors to help preserve the large flooring 

timbers that were more expensive to replace than 

the lumber covering the sides and the roof. Most of 

the construction was done by farmers to pay their 

poll taxes. The bridges were usually named for the 

nearest resident. (Chamber of Commerce 2011)

Four bridges were selected for laser scanning in Madison 

County: the Roseman, Imes, Hogback, and Cutler–Donahoe 

Bridges. Photographs of these bridges are shown in 

Figures 3–6.

Zumbrota Bridge

Minnesota’s only remaining truly historic covered bridge is 

located in the City of Zumbrota. Listed on the National Historic Register, it was originally constructed in 1869 and relocated in 1932, 1979, and finally in 1997. It currently spans 

the Zumbro River in the 65-acre Covered Bridge Park. Considered a lattice through truss design, it is now a pedestrianonly bridge that spans 120 ft. A special documentary of the 

bridge and its importance to the history of Zumbrota can be 

found at http://www.youtube.com/watch?v=EVFd1YwcHw

w&feature=related. As a measure of its importance to Zumbrota, an annual covered bridge festival occurs every June. 

A photograph of the bridge is shown in Figure 7.

On September 23–25, 2010, the Zumbro River flooded, 

creating a dangerous situation for the Zumbrota Covered 

Bridge. As Figure 8 illustrates, floodwaters rose to nearly 

the same elevation as the bottom of the bridge.

Three-Dimensional Laser Scanning 

and Data Processing

The laser scanning was completed by Sightline, LLC (Milwaukee, Wisconsin), a private firm that specializes in the 

use of laser scanning technologies with structures. Approximately 20–30 scans were completed for each bridge from 

a variety of angles using a FARO LS 880 laser scanner. 

Figure 9 shows a FARO laser scanner being used to 

inspect an historic covered bridge.

The scanning process consisted of scans that were completed by Sightline, and data processing was completed by 

the University of Minnesota Duluth’s Natural Resources 

Research Institute (UMD NRRI). The following steps were 

completed and an estimate of the time duration was provided for each step:

1. Paper “targets” are placed in numerous locations on the 

bridge for use in linking up to 30 individual laser scans 

together. Time duration: 2 person-hours.

2. A FARO LS 880 3D laser scanner was used to conduct 

the scan. The scanner is placed at several vantage points 

inside and outside the bridge, so that all visible surfaces 

of the bridge can be documented. Individual scans are 

Table 1—Background information on the historic covered timber bridges used in this 

study 

State City Bridge 

Year

built

Span

(ft)

Placement 

on National 

Register of 

Historic Places Design 

Wisconsin Cedarburg Red 1876 120 March 14, 1973 Lattice through truss 

Iowa Winterset Roseman 1883 106 September 1, 1976 Lattice through truss 

Iowa St. Charles Imes 1870 81 February 9, 1979 Lattice through truss 

Iowa Winterset Hogback 1884 106 August 28, 1976 Lattice through truss 

Iowa Winterset Cutler–Donahoe 1871 79 October 8, 1976 Lattice through truss 

Minnesota Zumbrota Zumbrota 1869 120 February 20, 1975 Lattice through truss 
Use of Laser Scanning Technology to Obtain As-Built Records of Historic Covered Bridges

3

completed in approximately 15–20 min. When a single 

scan is completed, it is saved to a computer as an .ls 

file. It is highly recommended that a computer with 

significant computing power and high levels of RAM 

memory be used to process the millions of data points 

created during the scanning process. Time duration: 

10 person-hours.

3. After all visible portions of the bridge have been 

scanned, the software files are linked using FARO 

Scene software. This software allows an individual to 

identify the targets placed prior to the scanning process 

and use them to link or attach one scan to another. It 

is also possible to filter, using various techniques or 

software, extraneous images (for instance, a vehicle 

traveling across the bridge or background vegetation). 

The process of linking two individual scans is repeated 

several times until all scans have been compiled into 

one large scan depicting the entire bridge. Time duration: 9 person-hours.

4. Once a bridge has been completely assembled using all of the individual scans, it can be exported as 

a point cloud, depicting all visible aspects and actual 

dimensions of the bridge. This cloud of data was then 

exported into AutoCAD software (Autodesk, Inc., San 

Rafael, California) using an add-in provided by Kubit 

USA (Houston, Texas). This add-in allows a user to import point cloud files in addition to the ones inherently 

recognized by AutoCAD 2011 and has additional modeling tools for working directly with point cloud data in 

AutoCAD. Once a point cloud has been exported into 

AutoCAD, it can be divided into multiple cross sections. This is done so that specific components of the 

bridge can be seen more clearly. From this point, twodimensional (2D) and 3D models of the bridge can be 

generated. Time duration: 40+ person-hours.

Results

Laser Scanning

A number of types of images can be presented from processing point cloud data. These images include a point cloud 

image resulting from only one scan, a point cloud image 

created from multiple scans, a parametric picture created 

from a point cloud scan, a point cloud image imbedded in 

AutoCAD, and 2D/3D AutoCAD images. These images can 

be created using FARO Scene software or AutoCAD 2011 

with a Kubit USA add-in.

As to the project activities, the majority of the scan processing for the Cedarburg, Wisconsin, bridge was completed 

by Sightline, LLC. The processing of the scan data for the 

Madison County, Iowa, bridges and the Zumbrota, Minnesota, bridge was completed by the UMD NRRI. The project 

team decided that based on the processing time estimates, 

detailed in-point cloud and 3D AutoCAD, data would be 

provided for the Cedarburg, Imes, and Zumbrota Bridges, 

with only point cloud data for the Hogback, Cutler–

Donahoe, and Roseman Bridges. All the digital points could 

be further processed to develop detailed dimensional information, as the point cloud images are considered accurate 

data. The point cloud images could also be further processed 

using Kubit USA add-ins for AutoCAD 2011. Each bridge 

scan and AutoCAD image is shown in the following 

sections.

Cedarburg, Wisconsin, Covered Bridge

Figures 10–17 show various images created from 3D laser 

scanning conducted during the project for the Cedarburg 

Bridge. This includes point cloud images and AutoCAD 

drawings created from the point cloud images. The Imes 

Bridge is the only Madison County Bridge where the point 

cloud data was used to create AutoCAD drawings. Our project team has all of the point cloud data that could be used 

in the future to create AutoCAD drawings for the other 

Madison County bridges (Hogback, Cutler–Donahoe, and 

Roseman) scanned during the project.

Imes Bridge, Madison County, Iowa

For the Imes Bridge, the data show the accurate dimensions 

and shape of the bridge at the time of scanning. No corrections were made to straighten any bridge members, such 

as would be done to create new construction drawings. Figures 18–23 show that the bridge is no longer perfectly plane, 

but that it has twisted and moved over time.

Roseman Covered Bridge, Madison County, Iowa

Figures 24–25 shows various planar views and point cloud 

images created from 3D laser scanning conducted during the 

project for the Roseman Bridge, located in Madison County, 

Iowa. These point images are fully dimensioned computer 

files that can be used to determine dimensions, skew of the 

bridge, deflection, and other characteristics as needed, without importing into AutoCAD or other software platforms.

Hogback Covered Bridge, Madison County, Iowa

Figure 26 shows various point cloud images created from 

3D laser scanning conducted during the project for the Hogback Bridge located in Madison County, Iowa. These point 

images are fully dimensioned computer files that can be 

used to determine dimensions, skew of the bridge, deflection, and other characteristics as needed, without importing 

into AutoCAD or other software platforms.

Cutler–Donahoe Covered Bridge, Madison County, 

Iowa

Figures 27 and 28 show various point cloud images created 

from 3D laser scanning conducted during the project for 

the Cutler–Donahoe Bridge, located in Madison County, 

Iowa. These point images are fully dimensioned computer 

files that can be used to determine dimensions, skew of the 
Research Paper FPL–RP–669

4

bridge, deflection, and other characteristics as needed, without importing into AutoCAD or other software platforms.

Zumbrota Covered Bridge, Zumbrota, Minnesota

Additional project funds were received from the Minnesota 

Local Road Research Board’s Operational Research Program (OPERA) to conduct 3D laser scanning of the most 

significant historic covered bridge in Minnesota, located in 

Zumbrota. The bridge, built in 1869 (and relocated several 

times), is now located in a city park and spans the Zumbro 

River. Figures 29–36 show various scalar images and point 

cloud images created from 3D laser scanning conducted 

during the project. These figures show each different type 

of possible image that can be created using FARO Scene 

software or AutoCAD 2011 with a Kubit USA add-in. These 

images include a point cloud image resulting from only one 

scan, a scalar image created from a point cloud scan, a point 

cloud image created from multiple scans, a point cloud image imbedded in AutoCAD, and 2D/3D AutoCAD images. 

All of the scan data, images, and figures were provided to 

the City of Zumbrota for any further processing as appropriate.

In contrast to the Imes Bridge, significant efforts were made 

to straighten the dimensions of the bridge in AutoCAD in 

an effort to create a drawing that could be used to construct 

a new bridge. This was a significant undertaking, and added 

nearly 40 h of processing time to data processing. This process creates a drawing that would be more consistent with 

the original construction of the bridge, not its current shape 

and condition (Brashaw 2010).

Rapid Prototype Development

Following processing and development of the 3D scanning images, a digital 3D CAD file was used to generate a 

1/100th 3D scale replica of the bridge at the Northern Lights 

Technology Center of UMD NRRI. In processing the data, 

we found that it would only be possible to produce an accurate external version of the bridge. We could not create 

a true replica of the inside of the bridge because a 1/100th 

scale of a 6-in.-wide beam would only have a thickness of 

0.06 in. This is below the thickness that can be created using 

rapid prototyping, and these thin members would not have 

strength because many of the beams and members are only 

connected at the ends. The 3D image that was used by 

the Vanguard unit to create the 1/100th model shown in 

Figure 37 from Vanguard Si2 selective laser sintering (SLS) 

equipment (3D Systems, Valencia, California) was used to 

create the scale replica of the bridge (Fig. 38). Because the 

scan data were corrected to achieve straight members, this 

model would be consistent with the true nature of the bridge 

at construction, not its condition in 2010. 

Comparison of Laser Scanning Equipment 

Results with Field Measurements

One of the objectives of this project was to assess the accuracy of laser scanning to determine accurate dimensions 

of the bridges. The FARO laser scanner used for the project 

was rated at an accuracy of 1/4 in. at a distance of 150 ft. 

However, the typical distance of the laser scanner in this 

project ranged from 50–100 ft, improving the accuracy over 

the rated number. For this phase of the project, only the 

Madison County, Iowa, bridges were measured to verify the 

accuracy. To conduct this task, digital photos of each bridge 

were taken as soon as the project team arrived. These photos 

were then printed on a portable printer and used to record 

the accurate dimensions measured with traditional tape measures (1/16-in. accuracy). 

Each bridge was then scanned using the laser scanner at up 

to 20+ locations. The raw scan data were processed into 

point cloud data. The locations measured using traditional 

measuring equipment on the photographs were then located 

in the digital files and the digital dimensions noted. Based 

on these data, a comparison between the actual and digital 

measurements was taken. The comparison data are reported 

for each of the four Madison County bridges in the following sections. Fourteen to sixteen locations were samples 

for each bridge with a very small error noted. This mean 

error of the 14–16 measurements ranged from 0.04–0.08 in. 

(1.01–2.02 mm), within the rated accuracy of 1/4 in. at 

150 ft.

Imes Covered Bridge, Madison County, Iowa

Figure 39 shows the locations on the bridges where the 

actual measurements were collected using traditional tape 

measures to a resolution of 1/16 in. Once the point cloud 

was developed from the multiple laser scans of a bridge, 

the data were extracted from the digital file and simply 

compared for accuracy. Table 2 shows the results of this 

comparison, showing that laser scanning is a very accurate 

means of determining dimensions for use in creating as-built 

documentation.

Hogback Covered Bridge, Madison County, Iowa

Figure 40 shows the locations on the bridges where the 

actual measurements were collected using traditional tape 

measures to a resolution of 1/16 in. Once the point cloud 

was developed from the multiple laser scans of a bridge, 

data were extracted from the digital file and simply compared for accuracy. Table 3 shows the results of this comparison, showing that the laser scanning is a very accurate 

means of determining dimensions for use in creating as-built 

documentation. 

Roseman Covered Bridge, Madison County, Iowa

Figure 41 shows the locations on the bridges where the 

actual measurements were collected using traditional tape 

measures to a resolution of 1/16 in. Once the point cloud 

was developed from the multiple laser scans of a bridge, 

the data were extracted from the digital file and simply 

compared for accuracy. Table 4 shows the results of this 
Use of Laser Scanning Technology to Obtain As-Built Records of Historic Covered Bridges

5

Table 2—Comparison of measurement data 

from traditional tape measures and point cloud 

measurements for the Imes Covered Bridge, 

Madison County, Iowa 

Member 

number

Method for measurement 

Tape

measurement

(in., to 

nearest 

1/16 in.) 

Point cloud 

Difference

between tape

and point cloud

(in.) (mm) 

3 points

(in.) 

Mean

(in.) 

1 2.88 2.68 2.73 0.15 3.77 

 2.76 

 2.74 

2 2.88 2.84 2.77 0.10 2.58 

 2.84 

 2.64 

3 11.25 11.40 11.21 0.04 0.93 

 11.20 

 11.04 

4 5.50 5.24 5.43 0.07 1.86 

 5.40 

 5.64 

5 11.50 11.32 11.30 0.20 5.08 

 11.20 

 11.38 

6 11.50 11.40 11.48 0.02 0.51 

 11.48 

 11.56 

7 11.75 11.72 11.73 0.02 0.59 

 11.84 

 11.62 

8 11.63 11.52 11.55 0.08 1.99 

 11.52 

 11.60 

9 11.75 11.76 11.79 0.04 0.93 

 11.80 

 11.80 

10 12.13 12.24 12.03 0.10 2.50 

 12.04 

 11.80 

11 1.75 1.76 1.69 0.06 1.44 

 1.68 

 1.64 

12 11.88 11.84 11.79 0.09 2.24 

 11.72 

 11.80 

13 11.63 11.84 11.60 0.03 0.64 

 11.44 

 11.52 

14 11.75 11.88 11.80 0.05 1.27 

 11.72 

 11.80 

15 12.00 11.96 11.95 0.05 1.35 

 12.08 

 11.80 

16 1.88 1.80 1.83 0.05 1.23 

 1.80 

 1.88 

Average difference 0.07 1.83 

Table 3—Comparison of measurement data 

from traditional tape measures and point cloud 

measurements for the Hogback Covered 

Bridge, Madison County, Iowa 

Member 

number

Method for measurement 

Tape

measurement

(in., to 

nearest 

1/16 in.) 

Point cloud 

Difference

between tape

and point cloud

(in.) (mm) 

3 points

(in.) 

Mean

(in.) 

1 8.00 7.96 8.03 0.03 0.68 

 8.04 

 8.08 

2 11.75 11.84 11.72 0.03 0.76 

 11.76 

 11.56 

3 12.00 12.16 12.07 0.07 1.69 

 12.04 

 12.00 

4 15.75 15.96 15.77 0.02 0.59 

 15.68 

 15.68 

5 11.38 11.20 11.33 0.04 1.06 

 11.28 

 11.52 

6 11.88 11.96 11.81 0.06 1.57 

 11.80 

 11.68 

7 11.63 11.60 11.59 0.04 0.97 

 11.48 

 11.68 

8 14.88 14.96 14.88 0.01 0.13 

 14.88 

 14.80 

9 11.38 11.20 11.28 0.09 2.41 

 11.40 

 11.24 

10 15.88 16.00 15.88 0.01 0.13 

 15.76 

 15.88 

11 11.50 11.40 11.51 0.01 0.17 

 11.48 

 11.64 

12 11.75 11.64 11.69 0.06 1.44 

 11.80 

 11.64 

13 12.00 11.84 11.89 0.11 2.71 

 11.84 

 12.00 

14 12.00 11.72 11.87 0.13 3.39 

 11.84 

 12.04 

Average difference 0.05 1.26 
Research Paper FPL–RP–669

6

comparison, showing that laser scanning is a very accurate 

means of determining dimensions for use in creating as-built 

documentation. 

Cutler–Donahoe Covered Bridge, Madison County, 

Iowa

Figure 42 shows the locations on the bridges where the actual measurements were collected using traditional tape measures to a resolution of 1/16 in. Once the point cloud was 

developed from the multiple laser scans of a bridge, data 

were extracted from the digital file and simply compared 

for accuracy. Table 5 shows the results of this comparison, 

showing that laser scanning is a very accurate means 

of determining dimensions for use in creating as-built 

documentation. 

Summary and Conclusions

This project successfully demonstrated the potential for using 3D laser scanning to accurately develop as-built documentation of historic covered timber bridges as a means to 

develop historical documentation. The following conclusions can be made from the project.

•	 Three dimensional laser scanning can be used to rapidly 

scan historic covered bridge structures. A number of 

technologies and commercial vendors are available. A 

commercial FARO scanner was used in this project and 

operated by using a phase shift technology rather than 

time of flight. This means that instead of a single pulse 

being reflected and the time of flight measured, constant 

waves of varying length are projected. Upon contact 

with an object, they are reflected back to the scanner. 

The distance from the scanner to the object is accurately 

measured by measuring the phase shifts in the waves 

of infrared light.

•	 Post-processing of scan data requires experience and 

skill to cost-effectively create as-built documentation. 

The staff at Sightline, LLC, was very efficient in linking 

the 3D scans, importing them into AutoCAD and creating detailed 2D and 3D CAD drawings. Our project 

student engineer faced a steep learning curve but developed an excellent skillset in processing the files during 

the project. For experienced staff, this technology can 

reduce the time associated with creating as-built 

documentation.

•	 A 3D scanner can be used to create a range of outputs 

that include point cloud scans, parametric images, and 

2D and 3D AutoCAD drawings. For historic covered 

bridges, this information can be used for a variety of 

purposes including as-built documentation and structural assessment, while also providing detail on the 

land topography adjacent to the bridge.

•	 One of the objectives of the project was to assess the 

accuracy of laser scanning to determine accurate diTable 4—Comparison of measurement data 

from traditional tape measures and point cloud 

measurements for the Roseman Covered 

Bridge, Madison County, Iowa 

Member 

number

Method for measurement 

Tape

measurement

(in., to 

nearest 

1/16 in.) 

Point cloud 

Difference

between tape

and point cloud 

(in.) (mm) 

3 points

(in.) 

Mean

(in.) 

1 11.63 11.76 11.62 0.01 0.13 

 11.50 

 11.60 

2 11.88 12.00 11.91 0.03 0.80 

 11.92 

 11.80 

3 11.88 11.96 11.84 0.04 0.89 

 11.72 

 11.84 

4 11.75 11.64 11.71 0.04 1.10 

 11.72 

 11.76 

5 11.88 11.76 11.79 0.09 2.24 

 11.84 

 11.76 

6 15.75 15.52 15.69 0.06 1.44 

 15.60 

 15.96 

7 11.63 11.72 11.61 0.02 0.47 

 11.50 

 11.60 

8 5.88 5.92 5.84 0.04 0.89 

 6.00 

 5.60 

9 11.50 11.52 11.47 0.03 0.85 

 11.48 

 11.40 

10 11.50 11.48 11.49 0.01 0.17 

 11.56 

 11.44 

11 11.63 11.76 11.71 0.08 2.07 

 11.72 

 11.64 

12 11.50 11.60 11.57 0.07 1.86 

 11.52 

 11.60 

13 16.00 15.96 15.97 0.03 0.68 

 15.96 

 16.00 

14 11.63 11.64 11.60 0.02 0.64 

 11.60 

 11.56 

15 11.63 11.56 11.61 0.01 0.30 

 11.68 

 11.60 

16 7.63 7.48 7.56 0.07 1.65 

 7.56 

 7.64 

Average difference 0.04 1.01 
Use of Laser Scanning Technology to Obtain As-Built Records of Historic Covered Bridges

7

mensions of the bridges. Each bridge was then scanned 

using the laser scanner at up to 20+ locations. Raw scan 

data were processed into point cloud data. The locations measured using traditional measuring equipment 

on the photographs were then located in the digital files 

and the digital dimensions noted. Based on these data, 

a comparison between the actual and digital measurements was taken. The comparison data are reported for 

each of the four Madison County bridges in the following sections. Fourteen to sixteen locations were samples 

for each bridge with a very small error noted. This 

mean error of the 14–16 measurements ranged from 

0.04–0.08 in. (1.01–2.02 mm), within the rated scanner 

accuracy of 1/4 in. at 150 ft.

References

Brashaw, B.K. 2010. Use of laser scanning technology to 

obtain as-built records of the Zumbrota covered bridge. 

NRRI Tech. Rep. NRRI/TR-2011/04. Duluth, MN: University of Minnesota. 

Chamber of Commerce. 2011. Madison County, Iowa—the 

bridges of Madison County [Website]. Winterset, IA: Madison County Chamber of Commerce. http://madisoncounty.

com/index.php?page=the-bridges. Accessed October 6, 

2011.

FARO Technologies. 2011a. FARO laser scanner training 

[Print presentation]. Lake Mary, FL.

FARO Technologies. 2011b. Measuring arms, laser tracker, 

laser scanner. In: FARO laser scanner focus 3D—applications. Lake Mary, FL. http://www.faro.com/focus/applications. 

Foltz, L. 2000. 3D laser scanner provides benefits for 

PennDOT bridge and rockface surveys. Professional Surveyor magazine. (May). http://www.profsurv.com/magazine/

article.aspx?i=590. 

Jaselskis, E.; Cackler, E.; Andrle, S.; Gao, Z. 2003. Pilot 

study on improving the efficiency of transportation project 

using laser scanning. Final Rep. CTRE Project 02-109. 

Ames, IA: Iowa State University, Center for Transportation 

Research and Education.

Ozaukee County. 2011. History of the covered bridge. 

Port Washington, WI: Ozaukee County public records. 

http://www.co.ozaukee.wi.us/history/bridge.html. 

(October 6, 2011).

Table 5—Comparison of measurement data 

from traditional tape measures and point cloud 

measurements for the Cutler–Donahoe Covered 

Bridge, Madison County, Iowa 

Member 

number

Method for measurement 

Tape

measurement

(in., to 

nearest 

1/16 in.) 

Point cloud 

Difference

between tape

and point cloud

(in.) (mm) 

3 points

(in.) 

Mean

(in.) 

1 11.63 11.60 11.55 0.08 1.99 

 11.64 

 11.40 

2 11.63 11.72 11.57 0.05 1.31 

 11.48 

 11.52 

3 11.75 11.60 11.71 0.04 1.10 

 11.76 

 11.76 

4 11.50 11.48 11.63 0.13 3.22 

 11.72 

 11.68 

5 1.75 1.76 1.73 0.02 0.42 

 1.64 

 1.80 

6 5.88 5.80 5.73 0.14 3.60 

 5.72 

 5.68 

7 3.75 3.68 3.76 0.01 0.25 

 3.80 

 3.80 

8 12.00 11.96 11.89 0.11 2.71 

 11.84 

 11.88 

9 11.50 11.56 11.64 0.14 3.56 

 11.56 

 11.80 

10 12.00 12.16 12.05 0.05 1.35 

 12.04 

 11.96 

11 1.63 1.64 1.64 0.01 0.38 

 1.72 

 1.56 

12 12.00 11.92 11.83 0.17 4.40 

 11.88 

 11.68 

13 5.75 5.68 5.71 0.04 1.10 

 5.72 

 5.72 

14 3.88 3.60 3.73 0.14 3.60 

 3.88 

 3.72 

Average difference 0.08 2.07 
Research Paper FPL–RP–669

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Figure 1. Photograph of the Cedarburg Covered Bridge 

(Cedarburg, Wisconsin), circa 1934. From the Library of 

Congress.

Figure 2. Recent (2010) photograph of the Cedarburg 

Covered Bridge.

Figure 3. Roseman Bridge, Madison County, Iowa (2010).

Figure 4. Imes Bridge, Madison County, Iowa (2010).

Figure 5. Hogback Bridge, Madison County, Iowa (2010).

Figure 6. Cutler–Donahoe Bridge, Madison County, Iowa 

(2010).
Use of Laser Scanning Technology to Obtain As-Built Records of Historic Covered Bridges

9

Figure 7. Zumbrota Bridge, Zumbrota, Minnesota (2011).

(a)

(b)

Figure 8. Zumbrota Bridge on September 23, 2010, during 

flooding on the Zumbro River. (a. Photo courtesy of kstp.

com, b. Photo courtesy of fox9.com.).

Figure 9. A FARO laser scanner used to scan a historic 

covered bridge.

Figure 10. Point cloud image of the Cedarburg Bridge 

(SightLine, LLC).

Figure 11. 3D AutoCAD image of the Cedarburg Bridge 

embedded in point cloud data (SightLine, LLC).
Research Paper FPL–RP–669

10

Figure 12. Dimensioned 2D AutoCAD® image of the 

Cedarburg Bridge (SightLine, LLC).

Figure 13. Dimensioned point cloud image of bridge entry 

on Cedarburg Bridge (SightLine, LLC).

Figure 14. CAD image of the Cedarburg Bridge (SightLine, 

LLC).

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Figure 15. CAD dimensions of ceiling structure of the 

Cedarburg Bridge (UMD NRRI).

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Figure 16. CAD drawing and dimensions of front 

entrance of the Cedarburg Bridge (UMD NRRI).

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Figure 17. CAD drawing and dimensions of side wall and 

trusses of the Cedarburg Bridge (UMD NRRI).
Use of Laser Scanning Technology to Obtain As-Built Records of Historic Covered Bridges

11

(a)

(b)

(c)

Figure 18. Point cloud images of the Imes Bridge (UMD 

NRRI).

Imes

Natural Resources Research Institute

Isometeric

View

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PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Figure 19. Isometric 3D AutoCAD image of the Imes Bridge 

(NRRI).

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PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Figure 20. Dimensioned 3D AutoCAD image of the Imes 

Bridge showing the existing rotation and out-of-plane 

nature of the bridge (NRRI).

Imes

Natural Resources Research Institute

Side View

11'-41

4"

91'-03

4"

82'-41

2"

57'-41

4"

1'

11'-11"

10'

4'-33

4"

4'-31

4"

15'-01

2"

2'-11

4"

9"

20'-9"

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PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Imes

Natural Resources Research Institute

Side View

11'-41

4"

91'-03

4"

82'-41

2"

57'-41

4"

1'

11'-11"

10'

4'-33

4"

4'-31

4"

15'-01

2"

2'-11

4"

9"

20'-9"

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Figure 21. Dimensioned 3D AutoCAD side view image of the 

Imes Bridge (NRRI).
Research Paper FPL–RP–669

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PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Figure 22. Dimensioned 3D AutoCAD internal side wall 

image of the Imes Bridge (NRRI).

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

PRODUCED BY AN AUTODESK EDUCATIONAL PRODUCT

Figure 23. Dimensioned 3D AutoCAD ceiling image of the 

Imes Bridge (NRRI).

Figure 24. Planar views of a single laser scan of the 

Roseman Bridge (NRRI). 

(a)

(b)

Figure 25. Point cloud images of the Roseman Bridge 

(NRRI). 

(a)

(b)
Use of Laser Scanning Technology to Obtain As-Built Records of Historic Covered Bridges

13

Figure 26. Point cloud image of the Hogback Bridge 

(NRRI).

(a)

(b)

(c)

(d)

Figure 27. Point cloud images of the Cutler–Donahoe 

Bridge (NRRI).

Figure 28. Point cloud image (enhanced with clear view 

software setting) of the Cutler–Donahoe Bridge (UMD 

NRRI).

(a)

(b)
Research Paper FPL–RP–669

14

Figure 29. First scalar image of the outside of the Zumbrota 

Bridge Point Cloud.

Figure 30. Scalar image of the outside of the Zumbrota 

Bridge created from a single exterior scan processed with 

Faro Scene software.

Figure 31. Scalar image of the inside of the Zumbrota 

Bridge created from a single interior scan processed with 

Faro Scene software.

(a)

(b)

(a)

(b)

Figure 32. Point cloud images of the Zumbrota Bridge 

created from multiple scans and linked together with Faro 

Scene software.
Use of Laser Scanning Technology to Obtain As-Built Records of Historic Covered Bridges

15

Figure 33. Point cloud images of the Zumbrota Bridge 

created from multiple scans and linked together with Faro 

Scene software, imbedded into AutoCAD with a Kubit USA 

add-in.

Figure 34. An AutoCAD 3D image of the Zumbrota Bridge 

created from scanning data.

(a)

(b)

(a)

(b)

(c)

Figure 35. AutoCAD 2D images of the Zumbrota Bridge 

created from scanning data.
Research Paper FPL–RP–669

16

(a)

(b)

(c)

(d)

Figure 36. Three AutoCAD 2D images (top 3) of wall 

components used to create a composite of the Zumbrota 

bridge wall.

Figure 37. A 1/100th model of the Zumbrota Bridge 

created using selective laser sintering rapid prototyping 

equipment.

Figure 38. A 3D isometric image of the Zumbrota Bridge 

used to produce a 1/100th model using selective laser 

sintering rapid prototyping equipment. 

Figure 39. Locations on the Imes Bridge where 

comparison measurements were taken using traditional 

tape measures and extracted from the digital point clouds 

created from the laser scanning process.

(a)

(b)

(c)
Use of Laser Scanning Technology to Obtain As-Built Records of Historic Covered Bridges

17

Figure 40. Locations on the Hogback Bridge where 

comparison measurements were taken using traditional 

tape measures and extracted from the digital point clouds 

created from the laser scanning process.

(a)

(b)

(a)

(b)

Figure 41. Locations on the Roseman Bridge where 

comparison measurements were taken using traditional 

tape measures and extracted from the digital point clouds 

created from the laser scanning process.
Research Paper FPL–RP–669

18

Figure 42. Locations on the Cutler–Donahoe Bridge where 

comparison measurements were taken using traditional 

tape measures and extracted from the digital point clouds 

created from the laser scanning process.

(a)

(b)