Here's an overview of spatial imaging technologies AEC engineers use to capture and collect data.
In most architecture, engineering and construction (AEC) projects, one of the first key tasks is to gather data on existing conditions. This might start with collecting historical data from available records, followed by some type of project-specific survey to more accurately map site topography and existing facilities. Additional surveys are typically required during construction and after completion to establish as-built conditions.
For years, AEC teams relied on conventional tools such as tape measures, transits, theodolites and levels to collect data, build base maps and document construction projects. As new technologies were developed, AEC professionals gained several options for data collection, along with improvements to conventional technology. Let’s take a look at four common technologies used to collect AEC data: LiDAR (light detection and ranging, or sometimes laser imaging, detection and ranging), laser scanning, photogrammetry and GNSS (global navigation satellite system).
LiDAR and laser scanning
LiDAR and laser scanning are similar technologies, with some subtle differences. Both rely on laser technology, which gained widespread use among AEC professionals in the 1980s and 90s, primarily for measuring distances and establishing alignments and level surfaces. By directing a laser beam to an object and measuring the time for the reflected beam to return to the receiver, laser-based tools enabled users to measure distances accurately with the push of a button. And since laser beams do not disperse appreciably, they proved highly effective for establishing alignments and level planes.
More recently, LiDAR has been used to capture large datasets by targeting an object or a surface with a laser and taking multiple measurements encompassing the area of interest. In conjunction with geolocated control points, the measurements can be used to establish coordinates at each point of measurement.
LiDAR systems may be ground-based or mounted on aircraft, such as drones, also known as uncrewed aerial vehicles (UAVs). Equipped with a laser scanner, along with GNSS equipment and an inertial navigation system, airborne LiDAR is often used to create 3D models of ground surfaces over widespread areas. Airborne systems can also be equipped with high-resolution cameras to capture imagery.
Laser scanning, which also uses controlled deflection of laser beams to capture or establish surface shapes, is often used to build 3D models of buildings, mechanical systems and other specific objects. It is typically ground-based. Laser scanning is also used in 3D printers to build physical objects based on coordinate data.
Both LiDAR and laser scanning typically produce point-cloud images, which consist of numerous 3D points that can be used to depict objects in computer-aided design (CAD) and building information modeling (BIM) systems. Point clouds often need manipulation to be converted to surface models or aligned with other 3D models or point clouds. Because of the large quantities of data generated by point clouds, the resulting datasets may also need to be “thinned” or downsized for practicality in CAD or BIM models. Software utilities and artificial intelligence (AI) can help with this process.
Photogrammetry
Photogrammetry has been used for mapping purposes since the early 1900s. While multiple types of photogrammetry have been employed, the most common AEC applications have used aerial photography and stereoplotters to analyze two or more photographic images taken from different positions. Using this information, photogrammetrists can determine 3D coordinates of select points and plot contour lines to create topographic maps.
With the development of LiDAR and other technologies, photogrammetry has also been used in conjunction with these technologies to produce a wide variety of maps and datasets. For example, since photogrammetry is generally considered more accurate in the X and Y directions (horizontal coordinates), while LiDAR is generally more accurate in the Z direction (vertical), the two technologies can be combined. By georeferencing aerial photographs and LiDAR data in the same coordinate system, 3D visualizations can be created with optimal accuracy and contain a wealth of data.
GNSS
A GNSS uses satellite data to provide positioning, navigation and timing (PNT) services on a global or regional basis. The U.S.-operated global positioning system (GPS) is one of many GNSSs in the world.
The U.S. Department of Defense initiated the U.S. GPS program in the 1970s. The full constellation of 24 satellites became operational in 1993. Initially, the accuracy of civilian GPS data was limited by a deliberate error introduced into the GPS data so that only military receivers could access the maximum accuracy. This limitation was removed in 2000. In the AEC world, most GNSS-based devices still combine satellite information with terrestrial-based corrections or augmentations to compensate for various imperfections and improve accuracy.
With a robust network of satellites, GNSS data can be captured by numerous devices, including smartphones, tablets and other consumer products. For professional AEC use, more sophisticated GNSS receivers are used to capture 3D point data more accurately. These devices can be manually positioned or mounted on vehicles for mobile use.
In addition to providing a convenient way to collect survey data, engineers use GNSS in many other AEC applications, such as automated construction layout, real-time guidance of construction equipment (machine control), tracking construction equipment and materials, monitoring worker safety and performance, and capturing project progress.
Selecting a method
With numerous data collection choices available, selecting the best method for any given project might seem like a daunting process. In addition to the individual methods described previously, sometimes multiple methods can be used together to achieve the desired results. And for small projects, sometimes conventional tools might still provide the most practical solution.
While there are no hard and fast rules for selecting the best method or methods, proper consideration of key factors and input from experienced professionals can simplify the process. Key factors to consider include:
- Level of accuracy — If the data will be used for final design and modeling purposes, greater accuracy will be required than if the data will only be used for planning purposes.
- Area of coverage — For large areas with high point-density requirements, airborne LiDAR might provide the best results. For smaller footprints with intricate facilities, ground-based laser scanning might be a better choice. Photogrammetry and GNSS can also be considered for projects of various sizes, either individually or in conjunction with one of the other projects.
- Availability of existing data — If a project owner already has data of the appropriate level of accuracy and in the vicinity of the project, but just needs additional coverage, sometimes sticking with the previous data collection method makes the most sense.
- Availability of services — Whether or not the project team has ready access to the various methods can play a part in the decision.
- Budget — Like it or not, sometimes cost plays a key role in selecting a method.
The decision-making team may need to be a multi-discipline group, considering planning, design, construction, and operational needs. An experienced geospatial professional should also be part of the decision-making process.
