Daryn Fitz
If you have ever considered using Digital Twins on a construction site, have you ever thought about the different types of positioning, mapping, or communication sensors you might have available to you? Within this blog post, we look at a few examples.
The most common mapping technology used in construction today is 3D laser scanning, also known as lidar. Most laser scanners use an emitted pulse's Time-of-Flight (ToF) which is used to calculate the 3D coordinates of points relative to the scanner. A digital camera may also be used to colourise the point clouds. The method of deploying laser scanners is varied from stationary mounts such as tripods to moving vehicles, including aerial.
Digital images acquired by RGB cameras combined with photogrammetric techniques can create 3D point clouds of any scale. The model generated via the point clouds can be scaled by georeferencing or performing additional measurements on-site. By mounting what are typically low cost cameras to UAV’s, hard to reach areas can be accessed and although it is not as accurate as laser scanning this method is a very viable low cost alternative.
Depth cameras may appear to be like laser scanning but there is a key difference, rather than capturing points they illuminate a whole scene with a pulse of radiation and simultaneously capture the reflected light. Depth cameras are embedded within everyday products such as smartphones and AR head mounted displays. It is no consequence that interest in these cameras for mapping purposes is increasing but there are limitations in range of 3-10 meters, and they can be interfered with by sunlight.
Virtual reality (VR) simulators are used for training across many different fields — from military operations to commercial pilot training. In construction, VR technology brings immense benefits for safety training. Workers can learn to operate specialised machinery in a safe environment, as well as train to deal with challenging work circumstances. VR like IrisVR’s tool can also be used to explore a BIM or 3D project.
In VR simulations, the whole environment is computer-generated and people can interact with it through special devices. In comparison, augmented reality (AR) superimposes interactive visualisations onto the real-world environment, which enhance the person’s experience. With AR, you can improve on-site safety while you’re at the jobsite. Employees can use AR equipment to check for hazards and ways to avoid them. For example, with Trimble Connect’s HoloLens hard hats, workers can review safety checklists for specific work areas while in their protective gear.
GPR is a non-intrusive technique to find buried subsurface objects via electromagnetic waves with the advantage that it can capture non-metallic objects such as rock, soil, water as well as cables, metals, and pipes. The data collected as waves is used to map the subsurface.
Using drones in the construction field is already a prominent practice. With their help, you can conduct site inspections in a new and safer way. Drones make jobsite monitoring much easier, affordable, and manageable.
Site surveys are faster and more accurate with drones, compared to using aerial imaging or an on-site crew. With a drone, you can gather richer information as well. You can make 3D and topographical models, measure volumes, and obtain high-resolution images of your sites.
Drones can also go places that are riskier for your crew. They can safely inspect buildings of any size and in any location, as well as viaducts, bridges, and various other types of buildings. You can also use drones to monitor on-site safety compliance.
New construction technology based on sensors allows you to provide safer working conditions to your employees. Construction wearables can be placed in the personal protective equipment or clothes of employees. They use GPS tracking, biometrics, environment sensors, and many other new functionalities to prevent accidents and monitor a person’s physical status. Wearables can track slips and falls and all sorts of movements, as well as heart, respiration rates, and temperature.
Site sensors can warn workers about potential hazards and make the jobsite safer. They can track noise levels, dust saturation, temperature, and the presence of volatile substances. Whenever there is a risk in a certain area, the sensors can let workers in the vicinity know.
Barcodes and QR codes are the most widely used technique for identification and data communication. However Radio Frequency Identification (RFID) is another technology and gaining popularity year on year. RFID Tags are wireless sensors used for short data communication and for determining the position of objects to which the tags are attached. The RFID tag is programmed to store digital data and send it to the reader when activated by a RF pulse. There are two types of tags Passive which requires no dedicated power source which has a communication range of 5-6 meters and Active which has a dedicated power source and an extended range, up to 100 metres. RFID tags can be used for many applications including asset tracking, inventory management, access management, personnel tracking, on-site inspection, ID badges, supply chain management, fleet tracking, gated community access, private parking access, and location of buried assets.
An Inertial Measurement Unit (IMU) consists of a group of sensors to measure acceleration (in three dimensions), angular velocity (in three dimensions) and magnetic field strength. These measurements can be used to estimate a device's position. Although IMUs do accrue measurement errors over time they have been used to measure worker productivity and for location tracking across construction sites.
GNSS is the most widely used outdoor localisation system that uses a satellite-based navigation system. The most popular system is the United States Global Positioning System (GPS), which uses a constellation of 24 active satellites to estimate in real-time the current position of a receiver. GNSS requires line-of-sight (LOS) communication between at least four satellites and the receiver and can achieve a positioning accuracy of up to five metres, but it is not suitable for use within buildings.
In contrast, Differential GNSS (DGNSS) systems utilise a network of base stations on the ground to provide a centimetre level of accuracy and has been used to track construction vehicles, materials and personnel.
There are of course many more sensors we could have listed above, but this short list illustrates how positioning, mapping and communication sensors have become embedded within our day to day lives and of course the construction sector. We have existing technologies and data that can provide that link between our real-world built environment and our digital representations enabling the formation of Digital Twins to support construction.
