There have been several approaches to integrating physical construction components and their virtual models using RFID tags. These enable the movement of components to be tracked on the construction site. However, there is inadequate support for bidirectional coordination between these components and their virtual representations. Also, these approaches often involve manual input of status information into the tags and do not support tracking the permanent installed position of tagged components for consistency maintenance between the as-built and the as-planned models. As such, there are difficulties with ensuring accurate and timely updating of building information models and tag information during the construction process. A major bottleneck in achieving this integration is the choice of appropriate mechanisms for binding physical components with their virtual representations. This paper presents an approach to facilitating bidirectional coordination between physical construction components and their virtual models. Specialized real-time location sensing (RTLS) tags were used for tracking the position and status of physical construction components. This approach showed significant opportunities for enhancing real-time construction consistency checking, which will aid proactive decision making and control. The paper also discusses experiments undertaken to demonstrate the proposed RTLS-based system and highlights the merits and demerits of adopting the proposed approach on a full-scale project.
Being able to accurately and efficiently monitor construction progress in real time enables project managers to detect schedule delays early and make corrective decisions [
A number of researchers [
Being able to track the permanent installed positions of tagged components enhances consistency maintenance between building information models and the physical construction. Also, there is a scope for the use of these models for enhancing the real-time bidirectional coordination between the design team and personnel on the construction site [
A cyber-physical systems approach to integrating the virtual models and the physical construction (for consistency maintenance and bidirectional coordination—Figure
Bidirectional coordination between virtual models and the physical construction.
A number of researchers have attempted to integrate virtual models and physical construction using RFID tags (passive and active tags). These technologies are used for identifying, tracking, and locating materials, vehicles, and equipment in the construction industry. The following research efforts have focused on the use of these technologies for progress and lifecycle management in construction projects: Chin et al. [
While the aforemantioned authors utilized passive RFID tags, Motamedi and Hammad [
Although, the aforementioned research has demonstrated the potential of RFID tags for integrating virtual models and physical components for progress monitoring and facilities management using RFID tags, the tags cannot automatically track location or placement of tagged components. Tracking placement of installed/uninstalled components is important in progress monitoring to ensure that the right equipment or component is installed in the right place with minimal manual effort. RTLS system has the potential for sensing the location of tagged components. This could be linked to the virtual model for status tracking. Also, the RTLS system has storage capability. Linking the tagged components with their virtual representation in the model will enable real-time communication between the design team and the construction site personnel, thereby enhancing bidirectional coordination. Bidirectional coordination will enable information such as design changes/model updates to be captured by the construction personnel on the job site in real time. This also supports the communication of as-built “status” information to the model. To enable bidirectional coordination, an approach is needed that will tightly integrate the virtual resources and the physical construction/components; this is termed the cyber-physical systems approach.
In the construction context, cyber-physical systems approach is taken to mean a tight integration and coordination between virtual models and physical construction/constructed facility such as to enable bidirectional coordination. The key features of a cyber-physical systems approach are the cyber-physical bridge and the physical cyberbridge is shown in Figure
Features of CPS for integrating virtual models and physical building components.
The key enabling technologies for cyber-physical systems integration such as to enable bidirectional coordination between virtual models and the physical components are discussed as follows.
The RTLS system obtained from Identec Solutions consists of real-time location sensing (RTLS) tags (i-Q350 RTLS), RTLS reader (i-PORT M 350 RTLS), satellite nodes (i-SAT 300 RTLS), and an “i-Share” position server. The overview of the RTLS system is shown in Figure
The RTLS tags (Figure
i-Q350 RTLS tag.
The i-SAT 300 RTLS (shown in Figure
i-SAT 300 RTLS.
The i-PORT M 350 RTLS reader, shown in Figure
i-PORT M 350 RTLS reader.
Component overview of the RTLS system.
i-Share Edgware is a server application with the primary goal of filtering data to and from the i-PORT M350 RTLS reader installation. The supported features contain handling of various RFID situations like position calculation and sensor data. In addition to this, the server controls the system status and exposes tag communication to business applications. In order to reduce the effort for system integration and avoid typical interface problems like serialization issues, all available interfaces are Web services based.
The location information captured by the RTLS reader is collected in the i-Share positioning software. The i-Share positioning software computes the actual position of that tagged a component with respect to the reference i-SAT nodes and the RFID reader. Likewise information written to the RTLS tags can be captured by the RTLS reader and stored in the i-Share software. The positioning software can be integrated with BIM and other project management applications for as-built documentation and for visualizing progress information.
Mobile devices have long demonstrated opportunities for improving the construction delivery process through providing access to information on site and means of collaboration between project participants. Mobile devices such as tablet PC and PDA have display screen for capturing information about design changes, comments, and relevant information that need to be relayed to the construction team in real time. The construction team can also use the mobile devices for embed information in the tags or directly to the i-Share software to be captured in the BIM in the office. The mobile devices serve as a great tool to communicate back and forth the construction site and the office. In the context of this research, a tablet PC was used. This was used to access model updates and changes. The tablet PC also provided means of embedding information in the tags to be updated in the model.
The communication network, such as Ethernet and Wi-Fi, plays a great role in enhancing effective integration between BIM and the physical construction. The RTLS reader connects to the positioning server using the Ethernet. The positioning server can be accessed by the project team using the Internet. The mobile devices can also be linked using Wi-Fi to enable information sharing and collaboration between the project team.
The system architecture is illustrated in Figure
Architecture for CPS integration of physical building components and the virtual model.
The sensing layer consists of the RTLS system, comprising the tags, reader, and i-SAT nodes. In this layer, the i-SAT nodes sense the proximity of the tags and send the location data to the tags. The RTLS reader reads the location data from each of the tags and this is captured in the positioning software (where the exact location of the tags is computed). Information can also be written to the RTLS tags from the construction site; this information is captured by the RTLS reader and can be viewed in the model in the office. In this layer, the RTLS system serves three purposes: identification of components, localization of tagged components, and capturing information about the tagged components.
This layer consists of the client devices (such as the PDA, tablet PC, and mobile phones). This layer serves the purpose of enabling access to the sensed information written to the RTLS tags (from the model). It also enables the construction personnel embed as-built information into the RTLS tags to be captured in the model.
This layer contains the Internet and wireless communication networks: wireless personal area networks (ZigBee and Bluetooth), wide area networks and local area networks (which use Wi-Fi to enable access to the Internet). This communication networks connect mobile devices to allow for collaboration and information sharing of the captured RTLS tag information between construction personnel on site. The communication networks also allow the data collected through the mobile devices to be transferred through the Internet to the software and database in the contents and application layer.
The contents and application layer contains the database server and the control applications such as the positioning server and project management applications. This layer collects location data from the RTLS tags and computes the exact location of the tags relative to all the devices in space. This layer also stores and is constantly updated with information written to the RTLS tags from the client devices and from the actuation layer. The control applications use the sensed data from the database to make control decisions which can be visualized using the virtual prototype in the actuation layer.
This layer contains the virtual prototype which is accessed through the user interface. The virtual prototype enables the user to visualize how the sensed information (from the contents and application layer) affects the system (showing which components are installed and uninstalled). The human interface enables the user to visualize and monitor the movement of the tags in the space. This layer also enables the user visualize the sensed information from the contents and storage layer. The user can also embed control decisions into the virtual prototype through the user interface to be accessed in the device layer.
In order to carry out the experiment, a prototype system was developed based on the architecture in Figure
A virtual model of a small-scale building was developed using Autodesk Navisworks. The model serves the purpose of enabling visualization of status of tracked building components and information captured from the project site. The model also enables embedding of model updates or critical information that needs to be communicated to the construction site in real time. Navisworks was utilized because it offers an open.Net application programming interface (API), which enables users to write custom plugins to drive Autodesk Navisworks from outside the graphical user interface (GUI) and automate tasks like changing material properties and embedding information in components.
A laboratory-scale physical prototype of the Navisworks model was constructed. The physical prototype (Figure
Laboratory-scale physical prototype (tagged).
In order to integrate the design model and the physical prototype, two applications were developed using Visual Studio.Net. These applications are described in more detail below.
This is the main entry point into Autodesk Navisworks. This plugin was used to invoke the features of Navisworks such as color and property values. This plugin creates and invokes an interface on the design model GUI (Figure
Interface of CPSPlugin.
A client application was developed to fetch information from, and write to, the RTLS tags. This application captures the information written to the tag and writes it to an Access database, to be read by the CPSPlugin. The client application also reads information written to the Access database and writes it to the associated tag. The client application was written using “Windows Forms,” in the VisualStudio.Net environment. Using the client application, the user initiates a connection to a Web service interface in Figure
Client interface to display read and write command buttons.
Hardware setup in the prototype system.
Figure
Whenever there is a design change or model update, the CPSPlugin captures this change and stores it in a database and in the Web interface where it is received by the i-Share software. The RTLS reader collects this information and writes it to the associated RTLS tag where it can be accessed on site. Also, the tag can be read and updated using a client application installed on the mobile device. The client reads and writes to that tag by connecting to the Web interface. Information written to the Web interface is collected and stored in the Access database where the CPSPlugin updates the associated element with the change.
One of the objectives of these experiments was to track when tagged components are installed and uninstalled. The principle adopted here is that the as-built locations (position coordinates) of the tagged components must be known. These as-built locations are input into the developed CPSPlugin as the tagged component’s final “installed” location. These position coordinates are captured in Figure
Door and Roof element status changed to “uninstalled” (red).
Another objective of the experiment is to demonstrate bidirectional coordination through enhancing communication of critical information between the virtual and physical components. This was achieved using the CPSPlugin. CPSPlugin has read and write features. The read feature enables the capture of tag information from the Access database and writing the information to the associated element in the model. Once CPSPlugin reads new tag information, the element is highlighted and the new information is updated in the TagData property value as shown in Figure
Element highlighted and TagData property updated with information.
To write to a tag on site, the user writes information to the “Write To Tag” textbox, selects the element (he wishes to write to) in the selection tree, and clicks on the “Write” button as shown in Figure
Element selected in selection tree and information in textbox.
The developed prototype system was tested on two different sites (indoors and outdoors).
The developed system was initially tested indoors in the Intelligent Systems Laboratory in the Department of Architectural Engineering at the Pennsylvania State University as shown in Figure
Map from indoor test for stationary tags.
Indoor site
Indoor site blueprint showing the i-SAT nodes and stationary tags
During the indoor test, false movements (multipath effects) were noticed from the RTLS tags while the tagged components were stationary. These false movements resulted in a number of false updates recorded in the model. Figure
(The notations T1, T2,…,T8 on each green and blue icon represent the tags, with the green tag showing the initial location while the blue tag location shows the final location. The line between the RTLS tags represents the path to movement.)
The developed system was also repeated in an outdoor environment in a park behind the Engineering Unit buildings at the Pennsylvania State University as shown in Figure
Map from outdoor test for stationary tags.
Outdoor site
Outdoor site blueprint showing the i-SAT nodes and stationary tags (with wireless networks switched off)
Outdoor site blueprint showing the i-SAT nodes and stationary tags (with wireless networks turned on)
The outdoor test was carried out under the following conditions: when the surrounding wireless networks was switched off and switched back on. The surrounding wireless networks were switched off to avoid disruption to the RTLS signals. Under this condition, less multipath effects were noticed as illustrated in Figure
(The notations T1, T2,…,T8 on each green icon represent the tags and show that there was no multipath effect at the outdoor site).
(Green and blue icons represent the tags, with the green tag showing the initial location while the blue tag location shows the final location. The line between the RTLS tags represents the path to movement.)
The experiment presented in this paper has demonstrated some potential for the use of sensing technologies for tracking actual placement of tagged components, specifically for progress monitoring and capturing as-built information during construction. This is a step further from the existing approach of manually embedding status information into the tags. The experiment was implemented indoors and outdoors. The indoor experiment helped to determine the suitability of the RTLS system in enclosed sections (e.g., partially completed buildings) during construction and in the constructed facility during the operations and maintenance phase. The outdoor test also helped to the suitability of RTLS system in an open environment such as a construction site for material tracking. The RTLS system showed some potential for real-time location tracking of the tagged components in the outdoor environment. The RTLS system proved more effective and with less multipath movement when deployed outdoors with the wireless signals switched off than when the wireless signals were on. The signals from the RTLS system seem to be disrupted indoors, as a result of the interferences from wireless signals (such as the Wi-Fi, Bluetooth, and ZigBee) within and outside the laboratory. The disruption can be observed from the false movement/multipath effects of the RTLS tags viewed from the indoor site blueprint. However, this disruption relates to tracking the placement of the tagged components. The issue of communicating changes to the job site, and obtaining feedback or as-built documentation in the model proved effective. Changes made on the job site can be written to the RTLS tags to be documented in the BIM. Conversely, the project team can embed notification of changes or alerts in virtual components; this can be captured on the project site (either through the RTLS tag or mobile devices). This process of being able to track and communicate permanent placement of tagged components between the virtual model and the physical construction illustrates the concept of bidirectional coordination. The presented experiment has demonstrated the potential of the RTLS system for bidirectional coordination. Bidirectional coordination is beneficial for access to real-time progress information and decision making. The approach also has great potentials for enhancing as-built documentation which is necessary for lifecycle management of the constructed facility. The outdoor test took place outdoor with walls, trees, and less wireless interference (while the wireless network was switched off and on) compared to the indoor environment.
There is need to extend this work further by investigating other sensing systems and algorithms to enable transitioning of tagged components from outdoor (staging area) to indoor (partially completed site) environment. This is being addressed in the next phase of this research.
The authors presented an investigation into the use of a RTLS system for cyber-physical systems integration of virtual models and physical construction such as to enable bidirectional coordination. This investigation was carried out by conducting two tests (outdoor and indoor) to determine the efficacy of bidirectional coordination between the virtual model representations of building components and the physical components themselves. The RTLS system proved more effective outdoors than indoors, as the location coordinates were more stable outdoors than in the indoor situation where high multipath movements were recorded, when the tagged components were stationary. However, despite the multipath effects encountered, the use of RTLS tags for tracking model updates/design changes on the site and also updating the model with as-built information was successful in both the indoor and outdoor environments. This bidirectional coordination is considered very important in the deployment of cyber-physical systems in the construction industry. Thus, there is considerable potential for the application of the RTLS system to other aspects of the construction project delivery process, facility management, and other operations. Also, further work on this project involves investigating other sensors and algorithms to aid continuous capturing of location data as components transition from an outdoor (staging area) to indoor (partially completed site) environment. This will need to be tested on the construction site to identify practical implementation constraints in addition to identifying further benefits.