High Definition 3D Laser Scanning
February 19, 2015
By By Peter Srajer, P.Eng. MMM Group
New tools are enabling engineers to survey and re-envision everything from vast industrial plants to civil structures with an extreme degree of precision.
From the January-February 2015 print issue.
Within the field of surveying, spatial data collection is undergoing a rapid evolution. The focus is on gaining ever higher levels of accuracy and precision, and to achieve this consulting engineers are adopting advanced technologies such as 3D laser scanning. This sophisticated technology is being used not just for topographical surveys of land and resources, but also for the detailed measuring and representation of as-built conditions in various types of projects, be they industrial plants, civil infrastructure, or buildings and heritage structures.
3D laser scanning can measure every rock, crag, rill and lump of dirt when conducting a topographic survey. In a structural survey it can measure every bolt and flange and every pipe and conduct, even in a narrow dark corridor. In addition the survey can be conducted safely away from the targets. This means that stockpiles can be surveyed without setting foot upon them; roads can be surveyed without working in traffic; and open excavation can be safely surveyed from high ground far from any moving equipment.
Exteriors and interior scans of buildings, plants and other infrastructure can be combined to create a full walk-through 3D model as well as a deformation analysis of the structures if the need arises. This is a toolset that when combined with other data sources can yield a comprehensive model, combining what exists and what is being envisioned to ensure a safe and efficient process.
How it works
3D laser scanning picks up thousands to millions of points per second, measuring everything within your area of interest. The technology creates what is called a “point cloud,” which in-turn can be used to create a 3D-model. This data can be exported to various standard CAD, GIS and 3D modelling programs.
At the same time that the device is picking up 3D points, it can also take high-resolution digital images which are then mosaicked together to create a single image. This image is merged with the point cloud to create a “3D-Photo.” Every pixel shown in the merged photograph has 3D coordinates, providing accurate measurements between features. Scanners can be statically mounted for high resolution scans of a specific area, or mounted on vehicles to scan longer linear features while moving.
Types of laser scanner
There are generally two types of laser scanner, each with its own features and usage areas:
• “Time of flight scanners” are usually of a longer range (more than 1,500 metres in some cases). They collect tens of thousands of points a second with a larger point spacing and a larger diameter laser spot size. These scanners are ideal for applications in mining or large area scale projects where centimetre-level precision is not required and where large or difficult-to-access features (stockpiles, mine faces), production or safety requirements dictate that the surveyor must remain at a greater distance.
• “Phase based and hybrid scanners” are generally used in plant site and industrial site settings where we need to locate smaller features such as pipes or conduits. The scanners have a level of precision that is critical to enable accurate modelling of these features. They can collect up to 1,000,000 points per second, and they can have millimetre level point spacing and laser spot sizes. The disadvantage is that their scanning range is effectively limited to around 200 metres. We have found that it is most efficient and practical to keep the range to around 100 metres or less for most indoor applications.
Phase based and hybrid scanners tend to use a target based system of registering the individual scans together. Registration is the process of tying multiple scans together to create a single point cloud dataset. The targets are used as readily identifiable and precise features that are visible in overlapping scans. It is possible to use existing features such as building corners, signs and utility features, but the targets generally need to be more precise so that they can be automatically picked up and processed by the scanner post-processing software. The targets can be a variety of types from spherical single colour globes, to flat black and white plates, and even printed paper targets in areas where you may not expect to be able to retrieve the targets due to safety or operational requirements.
All of these technologies have some interrelation to one another, so the user’s skills and workflow from one are transferable to another. Companies can leverage the training and software they have invested in one technology with newer technologies as they become available.
• Reduced field time
• Can work in complete darkness (photo off)
• Collect data in tighter time windows
• Provide project results faster
• Reduce time spent in hazardous locations
• Collect higher density, more complex and complete datasets
• Reduce rework and revisiting field locations; the scanner picks up everything in the line of sight, reducing the potential for “I wish we had picked that up as well.”
Another aspect of 3D laser scanning that sets it apart from other surveying technologies is the fact that it not only measures things spatially, but also provides an accurate and effective visual representation.
The point cloud can be overlaid onto the imagery and provide a stunning 3D composition. We can also make highly accurate measurements of the components, even down to the bolt size of a structure that we are scanning. In addition, the point cloud can be combined with other as-built or design data to check for conflicts. One recent use involved a scan of a tunnel and overlaying the outline of the train. The train could be run through the tunnel virtually to check for sufficient clearances and obstructions.
3D laser scanning can be used to provide:
• AutoCAD DWG & Revit 3D models
• ArcGIS models
• 3D PDFs
It can be a valuable tool for:
• Fly through video files
• Communicating topography visually
• Giving presentations and in discussions away from the field
• Checking for conflicts by adding in planned features and existing CAD and GIS features.
Future directions: hobbyists and professionals
3D laser scanning offers tremendous opportunities for safely collecting information in a way and at a level never before possible. More importantly, it makes the information available to a larger audience due to its more accessible visual presentation.
The next wave of surveying could take an entirely new direction, as high definition 3D laser scanners, their mobile counterparts, and the introduction of unmanned aerial vehicles have brought the ability to collect spatial data to an entirely different demographic. The use of such tools still resides in the hands of professionals to get the most of their use, but the advent of lower end sensors (hobbyist UAV’s, open source navigation software and guidance systems), as well as the proliferation of easy-to-use and access GIS software, will entail making changes in the industry. In fact, the wave of the future seems to be not so much on the data collection aspect, but on the ability to understand and make coherent decisions and supporting analysis based on the data — in essence turning the spatial data into value added information. cce
Peter Srajer, M.Eng., P.Eng., CLS is the advanced technologies manager – geomatics, and an associate partner, with MMM Group. He is based in Calgary.