38th International Symposium on Automation and Robotics in Construction (ISARC 2021)

Bridge Inspection Field Support and Inspection Method byHeat Map Using 3D Point Cloud Data in Japan
Kazuhiko Sekia, Aika Yamaguchib and Satoshi KubotacaGraduate School of Kansai University, Japan, EYESAY Co., LTD, Japanb
Graduate School of Kansai University, Japanc
Faculty of Environmental and Urban Engineering, Kansai University, Japan
E-mail: k078673@kansai-u.ac.jp, k422541@kansai-u.ac.jp, skubota@kansai-u.ac.jp
Abstract –It is inevitable that the decrease in Japan’s
working population due to the declining general
population, low birth rate, and ageing population willlead to a shortage of skilled infrastructure inspectors.
Therefore, it is important to improve and equalize thequality of inspection data, which are the basis forunderstanding the condition of bridges, to allocate
appropriate and optimal budgets, and to formulate
life-extension repair plans. It is also important toimprove the quality of inspection data, which are thebasis for assessing the condition of bridges, and toequalize the data so that the progression of damage
can be properly assessed, an accurate diagnosis canbe made, and appropriate measures can be planned.
In this study, we propose a method for supporting thefield inspection of bridges by visualizing
abnormalities using a heat map based on 3D point
cloud data representing the bridge to be inspected.
The proposed method is evaluated by infrastructure
inspectors, and the requirements and issues for thefield support technology are summarized.
Keywords –Bridge Inspection; Three-dimensional Point-cloud
Data; Heat Map; Digital Transformation

1

Introduction

1.1

Background

1.1.1

Status of bridge inspection

Japan has about 730,000 road bridges with a length of
2 m or more. Most of them were built during the periodof high economic growth and are rapidly ageing. By 2029,
52% of these bridges will be at least 50 years old. The
number of bridges managed by local authorities that are
subject to traffic restrictions due to ageing has tripled in
the 10 years between 2008 and 2018 [1]. Moreover, there161

are many bridges that are still in use 80 years after theirconstruction without major damage due to appropriate
repair and reinforcement.
In 2014, a 5-year periodic inspection was stipulated
to obtain the information necessary for proper
maintenance of bridges in order to avoid damage to road
users and third parties, avoid long-term malfunctions andfailures, and enact timely measures to extend theirservice life [2]. During periodic inspections, thecondition of the bridge is assessed visually, a diagnosis
of soundness is made for reference, and countermeasures
to be taken before the next periodic inspection are
established. In addition, data on the external condition
and the degree of damage are obtained for comparison
with the results of previous inspections and to study the
maintenance plan. It is also important to transfer the
information from the inspection results and repairs.
However, because of the large number of bridges andparts to be inspected, it is time-consuming for inspectors.
1.1.2

Use of digital transformation
infrastructure sector

in

the

The Ministry of Land, Infrastructure, Transport andTourism (MLIT) set up the “Digital Transformation (DX)
Promotion Headquarters for the Infrastructure Sector of
MLIT” on 29 July 2020 [3]. As a result, MLIT uses data
and digital technology in the infrastructure sector totransform social infrastructure and public services in
response to the needs of the public, by transforming thework itself, the organization, the processes, and theculture and working style of the construction industry and
MLIT, and by promoting public understanding of
infrastructure. MLIT has established a policy of
promoting public understanding of infrastructure andrealizing safe, secure, and prosperous lives. The
introduction of advanced and new technologies is
indispensable for the introduction of new technologies
and the measures to achieve them, such as Society 5.0
and DX. In addition, MLIT is promoting “i-Construction,”
which aims to increase the productivity of construction

38th International Symposium on Automation and Robotics in Construction (ISARC 2021)

sites by 20% by 2025 through the use of information andcommunications technology and 3D data in all
construction processes. With these initiatives, sharing
information on bridge inspections with 3D data will
improve the efficiency of inspection efforts and enable
rapid response in an emergency. In addition, the use of
3D data for bridge maintenance and management will
make it possible to easily grasp the location and extent ofdamage, as well as the overall bridge condition, which
will be useful for determining the cause and diagnosis ofbridge deterioration [4]–[8].

1.2

Objectives of this study

To improve the efficiency of bridge inspection work,
this study proposes a bridge inspection field support
technology as a method to determine the damage of
surface irregularities from the 3D data of bridges, toefficiently evaluate overall bridge damage, and tovisually grasp the change and position of damage overtime. In this paper, we propose a new method forvisualizing the damage of a bridge using 3D point clouddata. The 3D data are acquired by photogrammetry usinga camera or a ground-based terrestrial laser scanner(TLS).
To improve the efficiency of the periodic inspectionof bridges, we propose a bridge inspection method thatuses a heat map to generally check the appearance ofbridges before visual inspection and to screen the bridges
or bridge components to be inspected.
The contribution of this research is that we haveclarified a method to analytically visualize the ageing
process using point cloud data sets. The method wasapplied to support bridge inspections, and actual
practitioners (inspectors) evaluated the method.

1.3

Research flow

2

Status and challenges ofmaintenance and management

2.1

Status of bridge maintenancebridgeIn December 2012, the Sasago Tunnel was closed fora long time as a result of a fallen ceiling plate whichclaimed the lives of nine people. This incident reaffirmed
the importance of maintaining and renewing social
infrastructure, and in March 2014, regular inspections byclose observation every 5 years became a legal
requirement. From 2014 to 2018, mandated inspections
were carried out based on the 2014 edition of the Periodic
Inspection Guidelines for Bridges. Bridges under the
direct control of the national government were inspectedaccording to the periodic bridge inspection guidelines,
while bridges under the control of local authorities were
inspected according to the periodic road bridge
inspection guidelines. However, in 2019, the periodic
bridge inspection guidelines were revised to streamline
the inspection process while ensuring the quality of
periodic inspections, in response to the occurrence andoversight of deformations that may affect the safety ofthird parties after periodic inspections and thedevelopment of inspection support technologies, such as
photography and non-destructive testing [10], [11]. In therevised guidelines, the focus of periodic inspections is on
the damage and structural characteristics, and theinspection targets are narrowed down to streamline theinspection process. In addition, guidelines for the use of
new technologies and a performance catalogue [12] havebeen developed to supplement, replace, and enhanceclose visual inspection.

2.2

Challenges in bridge maintenanceBridge maintenance has three main challenges.

The research flow of this study is as follows.
In Section 2, we summarize the status and issues ofbridge maintenance management since the Sasago
Tunnel ceiling plate failure accident, and how to use 3D
data to prevent such failures.
In Section 3, we set up field situations and summarize
how to make a heat map. In this section, we present theresults of experiments based on the contents of
In Section 4, we conduct a demonstration experimentbased on the procedures in Section 3. The contents of theexperiment, the results obtained, and the issues to beaddressed are summarized.
Finally, in Section 5, we interviewed inspection
practitioners about the application of heat maps to the 3D
damage drawing support system [9] previously
developed by the authors. This paper reports therequirements for the field support technology and system,and the issues in applying the system to practice.

162

2.2.1

Limited budget

The budget for the maintenance and repair of national
highways under national government control should be
increased to cope with the ageing of facilities, but it has
decreased by about 20% from 320.2 billion yen in 2004
to 251.5 billion yen in 2013, in line with the decrease in
the national public works budget [13]. In 2012, a disasterprevention and safety subsidy were established, andfinancial support and budget increases were implemented,
such as priority allocation for inspection and repair
projects for bridges and other structures. In 2012, thegovernment established the Disaster Prevention and
Safety Grant, which provides financial support andincreases the budget for bridge inspection and repair
projects.

38th International Symposium on Automation and Robotics in Construction (ISARC 2021)

2.2.2

Underutilization of technology that could
improve efficiency

The revision of the inspection guidelines has led tothe development of guidelines and performance
catalogues for the use of new technologies thatcomplement, replace, or enhance close visual inspection,
but their use is still limited.
2.2.3

Lack of human resources and skills

As of June 2019, there were no civil engineers
involved in bridge maintenance work in about 30% of
towns and 60% of villages, and 54% of direct inspections
and 42% of inspectors commissioned by local
governments had not taken the road management
practitioner training course or the road bridge
maintenance skills course conducted by MILT. In
addition, many bridges have been reported to require
repair or reinforcement after the first round of mandated
inspections, so human resources have been allocated to
repair planning, design, and implementation.

2.3

Using 3D data to solve problems

In this study, we propose an inspection support
technology that obtains 3D data of a bridge, creates a heat
map from the data, and visualizes damage points as a 3Dmodel to improve the efficiency of on-site work forbridge inspectors. We believe that this technology can
improve the efficiency of inspection work by detecting
damage from abnormalities identified by the heat map
and extracting locations should be focused on during
inspections.
To solve the problems of insufficient budget,
technical skills, and manpower, local surveyors who do
not specialize in bridge design have been commissioned
to carry out bridge inspections, and inspections have been

simplified and carried out by local government
employees (in-house inspections) [14]. However,potential problems include inspectors lacking sufficientknowledge about bridges and bridge damage, reductionin accuracy of the inspection due to simplification,differences in results between first and second
inspections, and damage that had been previously
identified being missed. The 3D data can be deployed ina 3D maintenance management system. By recording
damage data as a heat map or 3D data and bringing it to
the site, the risk of missing previously identified damage
will be reduced. In addition, quantitative evaluation of
the degree of damage from the heat map will reduce thevariability of evaluation among inspectors.

3

Heat mapping and visualization of
anomalies

3.1

Visualization of anomalies with heat maps

The process flow for creating a heat map from point
cloud data is shown in Figure 1. A camera and TLS areused to measure the bridge. Images or movies taken by
the camera are cut out at regular intervals to generate 3D
point cloud data with structure from motion (SfM)
processing to recover the shape from the images. The
difference between the point cloud data generated by the
SfM process or the TLS process and the reference data,
which simulate the undamaged surface, is visualized by
the colour change. The heat map is created using the point
cloud processing software CloudCompare. In thecomparison, first, by using the align function of
CloudCompare, feature points in the acquired point clouddata of two periods are manually selected, aligned, andsuperimposed. Next, the compute cloud/cloud distanceand compute cloud/mesh distance functions are used to

Figure 1. Flow of heatmap creation

163

38th International Symposium on Automation and Robotics in Construction (ISARC 2021)

perform a difference analysis of the two superimposed
data sets and create a heat map. The difference between
the two data sets is represented by a change in colour, forexample, a change to blue if the bridge is concave or to
red if it is swollen.

3.2

Damage to the detection object

Damage that can be detected using a heat map
includes dampness, delamination, exposure of steel bars,
and cracking of concrete members, as required by theperiodic bridge inspection guidelines.

3.3

Equipment used

In this study, to obtain 3D point cloud data for bridges,
we use FARO Focus 3D X330 as the TLS and SfM
technology to generate high-density point cloud datafrom images taken by a camera (GoPro Hero9 Black).

3.4

Heat map creation

To create a heat map from the 3D point cloud data ofa bridge, two field situations were set up. The first is acase where previous cloud data for the target bridge areavailable, and the second is a case where no previous
point cloud data are available. When previous point clouddata are available, the past and present point cloud data
are compared. The flow of the comparison with previous
data is shown in Figure 2. The point cloud data of two
periods are aligned so that the same positions overlap, thedifference analysis is performed using the previous data,
and a heat map is generated by setting the threshold. In
addition to analysis of differences in the point cloud data
by TLS (method (1)) and analysis of differences in the
point cloud data by SfM (method (2)), comparison of the

TLS point cloud data and SfM point cloud data is carriedout on the assumption that the measurement method isdifferent between the present and the past (method (3)).
The heat map patterns are shown in Tables 1 and 2. Whenprevious point cloud data are not available, a reference
plane that simulates the undamaged surface is created andcompared with the point cloud data. The reference plane
should be the same as that of the bridge when it was built,
but if as-built data or drawings are not available, thereference plane is made from the current measurement
data. The reference plane in this study is created by using
the Primitive Factory function of CloudCompare(method (A)), the 3D parametric model [15], [16]constructed for the bridge of interest (method (B)), andthe RANSAC function [17] (method (C)) to generate theplane from the point cloud. See Figure 3 for details.

4

Demonstrations

4.1

Content and results of the experiment

The proposed method was tested on two bridges, theWarazuhata Bridge in Sennan City, Osaka Prefecture(22.1 m long by 4.0 m wide), and an unnamed bridge in
Saitama Prefecture (2.0 m long by 4.5 m wide), as wellas on laboratory buildings on the campus of Kansai
University ‘Figure 4’. Previous point cloud data wereavailable for Warazuhata Bridge. At the Warazuhata
Bridge and the laboratory buildings, paper clay and wall
stickers with a thickness of about 1 to 2 cm were attachedto the abutments to simulate damage ‘Figure 5’. The dataobtained before sticker application were as previous data
and the data after application of the stickers were used as
current data. The camera was pointed at the front of theabutment and moved to the side. In the TLS measurement,

Figure 2. Flow of comparison between past and present datawhen historical point cloud data are available164

38th International Symposium on Automation and Robotics in Construction (ISARC 2021)

Table 1. Patterns of heat map creation when
historical point cloud data are available

Table 2. Patterns of heat map creation when
historical point cloud data are not available

Measurement type
The past
Current

Creation pattern
(1)

TLS

TLS

(2)

Camera (SfM)

Camera (SfM)

(3)

TLS

Camera (SfM)

Creation pattern
(A)
(B)
(C)

How to create a reference plane
Reference plane created using Cloud
Compare's Primitive factory function
The plane of the 3D parametric modelis the reference plane
Reference planes created from point
cloud data using the RANSAC
function(A) Flow of comparison with reference plane(B) Flow of comparison with 3D model(C) Flow of comparison with automatically generated criteria
Figure 3. Flow of comparison between reference plane and current point cloud datawhen no historical point cloud data are available

165

38th International Symposium on Automation and Robotics in Construction (ISARC 2021)

upper part of the abutment, it was not possible to compare
the damage of the entire abutment.
On the unnamed bridge, concrete spalls were widely
observed on the underside of the deck in the field, as
shown by the orthographic image in Figure 9. Extensive
delamination and exposure of steel bars were also
observed. In this study, the current SfM point cloud data
were used to verify the results in the absence of previous(L) Warazuhata Bridge, Osaka Prefecture(R) Unnamed bridge, Saitama Prefecture

Figure 6. Heatmap of Warazuhata Bridge Method(1) (TLS/TLS)(L) General view (R) Enlarged view

Kansai University laboratory buildings(L) 5th laboratory building(R) 4th laboratory building
Figure 4. Settings of the experiment

Figure 7. Experimental building Heat map of
method (2) (SfM/SfM)
Figure 5. Paper clay and wall stickers pasted on thevertical wall of the abutment of Warazuhata Bridge
the camera was placed in front of the damage and the 3D
data were constructed using FARO SCENE dataprocessing software. The heat map of the Warazuhata
Bridge is shown in Figure 6.
The colour of the heat map was set so that the amountof difference increases from green to red. The area where
the pseudo-damage was pasted is drawn in bright green,
unlike the surrounding area. From the figure, the damage
can be visualized by the colour change. Figure 7 shows
the results for method (2), comparison of SfM point clouddata. Like method (1), a colour change was observed at
the point where the pseudo-damage was pasted, but
relative to the comparison with method (2), the colourchange was also observed at points other than where thepseudo-damage was pasted. This may be due to theinferior accuracy of the SfM point cloud data comparedwith the TLS point cloud data. Similarly, in method (3),where TLS and SfM point cloud data are used ‘Figure 8’,
damage can be confirmed from the heat map. As withmethods (1) and (2), a colour change was observed at the
point where the pseudo-damage was pasted, and thedamage could be visualized by the heat map. However,
because the SfM point cloud data did not measure the166

Figure 8. Heat map of Warazuhata Bridge Method(3) (TLS/SfM)

Figure 9. Orthoimage of the underside of the main
deck of the unnamed bridge

Figure 10. Heat map of the unnamed bridge using
method (A)38th International Symposium on Automation and Robotics in Construction (ISARC 2021)

data. Figure 10 shows the results of visualization of thedamage by aligning the reference plane created bymethod (A) using the Primitive Factory function of
CloudCompare on the SfM point cloud data.

4.2

Considerations

In this study, the heat map was made according to theflow diagram shown in Figure 1. The experimental
results showed that the position of the pseudo-damage
and the position of the delamination coincided with theposition of the colour change in the heat map, suggestingthat the waviness and delamination of concrete can bevisualized. This suggests that the proposed method isreasonable. However, cracks in the concrete were notvisualized by a colour change in the heat map. It was
found that the heat map could visualize damage thatcreated unevenness, such as waviness and delamination,
but could not visualize damage without unevenness or
small damage such as cracks. By creating heat maps fromthe point cloud data from two different periods, it ispossible to see the change over time and to identify thetime when the damage occurred. In the absence of point
cloud data from two different periods, it is difficult todetermine the most appropriate among the three methods
because it takes time to align the planes to visualize thedamage. and a suitable for creating the reference planediffers depending on the measured data. As shown in
Figure 8, the heat map shows a colour change in areas
where the pseudo-damage is not pasted, which is more
extensive in the SfM point cloud data than in the TLS
point cloud data. This may be due to the difference inaccuracy between the TLS and SfM point cloud data.
Because TLS point cloud data are more accurate than are
SfM point cloud data, it is possible to use TLS as thebasic measurement method, and to use a camera when
TLS cannot be installed or when measurement isdangerous. The threshold value of the heat map waschanged for each bridge or building to make damage
detection easier. However, to evaluate bridges with thesame standard, the threshold value should be kept
constant. Because the SfM point cloud data are different
from the actual size of the bridge, it may not be possible
to visualize the damage if the threshold is kept constant.
As a solution to this problem, we propose a method forvisualizing the damage with the same threshold value forall bridges by adding location information to the SfM
point cloud data. In addition, it is thought that damage
can be quantitatively evaluated by this method.

5

Application as a bridge inspection
support technology and as a bridge
inspection method
The authors have developed a support system for

167

creating 3D damage diagrams to enable maintenanceworkers to grasp and share the location and status ofdamage intuitively and accurately. Since the heat map
information proposed in this study is also based on 3D
point cloud data, it can be superposed on this system.
Therefore, we conducted an evaluation meeting bypractitioners to evaluate the effectiveness of using heat
map information on mobile devices for inspection workin the field. The main opinions raised at the evaluation
meeting are as follows.
•
•

•

•
•

A heat map showing the areas to be focused on
during the field survey will improve the efficiencyof the field work and save time.
By looking at the changes over time, 10 years ago,
5 years ago and now, it is possible to understand thetrend of damage and make use of this informationin the inspection. However, care should be taken to
avoid focusing too much on old damage.
In the case of inexperienced practitioners, thesupport is likely to be more effective, while in thecase of experienced practitioners, quantitativeevaluation is needed, not just finding support.
Differences must also be able to be correctly
evaluated for point cloud data generated bydifferent la-ser scanners and cameras used.
It is difficult to use this method in general becauseof the limitation that the results are different depending on the location of the machine and theweather conditions. However, it is thought that the
restriction can be solved by organizing the methodof measurement, the method of setting up themachine and the method of analysis andformulating the guideline.

For the heat map to be used as a "bridge inspection
method" in periodic inspections, it is essential to increase
the number of demonstration tests, improve the accuracy
verification, and be able to quantitatively evaluate thesize and depth of damage. However, it is suggested thatthe method can be used in some bridge conditions, suchas where there is no third-party damage, or where there
is little road traffic, or where the bridge is not on an
important route.

6

Conclusion

In this study, to help infrastructure engineers carry out
bridge inspection in the field more efficiently, we haveproposed a method for detecting damage before the fieldsurvey by constructing a heat map based on 3D point
cloud data measured by TLS and photography during afield survey before the regular inspection. In this study,
we measured a bridge using TLS and a camera andconstructed a heat map with 3D data. The method ofusing the results with the 3D data was evaluated by38th International Symposium on Automation and Robotics in Construction (ISARC 2021)

inspection practitioners, and the issues and points to be
noted were summarized. In the future, we will study how
to use heat maps to visualize and detect damage withgenerally smooth features, such as narrow cracks, andhow to evaluate damage quantitatively by adding
location information to point cloud data. In addition, weplan to conduct more experiments to verify the accuracyof the method and clarify the range of application.

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