Our last blog post explored why Reality Computing is particularly well suited for civil infrastructure projects. The next several posts will look at the three components of Reality Computing—capture, compute, and create—through the lens of a civil engineer.
Capturing the physical world
For civil infrastructure projects, the physical world is usually digitally captured using photogrammetry, ground penetrating radar, or 3D laser scanning. New capture capabilities are being introduced in ever more varied devices, such as scanners or digital cameras mounted on drones.
Some of these data capture techniques have been used for decades to produce high-resolution models, but were cost prohibitive for most projects. In the past several years, new technology (in the form of both hardware and software) makes capturing the physical world less expensive and time consuming. For example, 3D laser scanning (also called LiDAR) is a relatively new technology that is quickly becoming an infrastructure industry standard for collecting data. The accuracy and sheer quantity of the data, and the speed at which it can be gathered, is opening up new possibilities in a sector that has been technologically stagnant for many years. Though many design and construction firms outsource data capture services, there is a growing trend for insourcing these capabilities as the technology becomes more accessible and no longer requires specialty firms or training.
3D laser scanning is quickly becoming an infrastructure industry standard for collecting data. Airborne laser scanning is used to capture 3D data for large areas, such as urban areas, industrial plants, or large transportation or land development projects.
Existing conditions are often captured using a variety of technologies. For example, to document the existing conditions of an airport, the runways and surrounding terrain could be captured with laser scans, supplemented by traditional survey information for positional accuracy. Digital photography and photogrammetry software could be used to document the airport terminal and other existing structures.
In addition, the power of cloud computing and social networking helps firms process and share existing conditions data more quickly and easily. This allows project teams to access and incorporate captured reality data from multiple sources, and combine that data with other existing spatial or geographical information such as GIS data, ground survey information, and digital terrain models to more completely reflect existing conditions.
3D Laser Scanning
There is a variety of 3D laser scanning methods. For civil infrastructure projects, the most common are airborne laser scanning, mobile, and terrestrial.
- Airborne laser scanning is used to capture 3D data for large areas, such as urban areas, industrial plants, or large transportation or land development projects. High-altitude capture typically involves sensors mounted on fixed wing aircraft, along with equipment to capture and calculate additional data about the movement of the plane to compensate for the motion. Due to the height, high-altitude 3D scanning is less accurate than other laser scanning techniques; horizontal positions can be off by as much as a meter. Nevertheless, for large-scale topography, it is faster and more accurate when compared to other methods, and the scans can be used to capture a variety of information including terrain, building locations, vegetation, utilities, roadways, and water features.
Low-altitude capture is similar to high-altitude, except that helicopters or drones are typically used, and the resulting data is more accurate. Low-altitude scanning is often used on large surveys of transportation or utility corridors. For example, a low-altitude airborne survey of a highway could be accurate enough for repaving plans or the design of new features like expanded shoulders.
- Mobile laser scanning systems use scanners mounted on moving platforms (such as vans or off-road vehicles). Like airborne scanning, these systems include equipment to calculate and compensate for the vehicle’s location and movement. These systems can quickly produce topographic surveys of drivable corridors. Most commonly used to capture data from a road, these systems can operate while traveling at highway speeds without exposing workers to traffic or requiring road/lane closures.
- Terrestrial laser scanning uses tripod or handheld scanners to capture information (both indoors and outdoors) about conventional topography, buildings, or smaller-scale infrastructure such as dams, small sections of roads, roadway intersections, or bridges.
Other Capture Methods
Digital photographs and photogrammetry can sometimes be a viable alternative to mobile or terrestrial laser scanning. Close-range or aerial photogrammetry can be a faster, less-expensive capture method for smaller scale civil infrastructure projects, such as bridges and roadway intersections.
Underground scanning using ground penetrating radar (GPR) and thermal imaging can also be used to capture existing conditions in the area of infrastructure projects. These methods can be used to locate buried structures, map underground utility lines, or detect other buried objects in the ground. GPR can also be used to non-destructively test the integrity of reinforced concrete structures, investigate concrete or masonry retaining walls or sea walls, and map the spacing of rebar.
Underwater laser scanning (with underwater laser scanners or sonar) are the primary methods for underwater surveying and inspection. Sonar is the more common technology, but underwater laser scanning provides more accurate measurements, which can be particularly useful for identifying cracks and erosion of underwater structures.
Safety and Access
Beyond providing very accurate existing conditions information, 3D laser scanning and these other methods of digital data capture can also be invaluable in assessing areas that are difficult or dangerous to access. For example, scanners mounted on drones can be used to capture the face of a dam or the topography of open pits, or inspect the condition of underground mines during construction or extraction to review safety or calculate volumes. For dangerous environments such as collapsed tunnels or mines, failed construction areas, high-voltage transmission stations, or radioactive sites, 3D laser scanners mounted on robots or drones can safely capture the physical conditions.
3D laser scanning and other methods of digital data capture can be invaluable
for assessing areas that are difficult or dangerous to access.
Working with Reality Data
Reality Computing relies on data that captures the rich detail and variety of the physical world. This format of this data is typically point clouds (from laser scanning) or high-density 3D meshes (from photogrammetry). This data is very different from the descriptive and analytic geometry commonly associated with CAD or BIM software tools. Some scanning technology captures both XYZ coordinates and color, producing point clouds that are visually easy to understand—much like a 3D panoramic photograph that you can walk through.
The next post will explore how captured reality data can be brought into 3D modeling software to provide physical context during the design, construction, refurbishment, or management of infrastructure.