Also referred to as high-definition surveying or HDS, laser scanning is a method of mapping positional data of a site. Laser scanning is a highly efficient way to perform the surveying for a project. It creates not just more data but more accurate data about the site than traditional surveying methods, while requiring only a fraction of the labor.
Here’s how the process generally occurs: A rotating laser measures the position of millions of points around the site. Software interprets all of this date to produce a 3D representation of the existing conditions. The operator places the laser at a handful of locations around the site, and the data from all these readings is compiled to create an existing layout and 3D model of the entire site. A single person often surveys an entire building site within a day, or even a few hours.
In addition to the usual topographical data obtained by older surveying methods, laser scanning provides accurate positional data of all existing topography and structure. This is very helpful for projects with any existing structure to be demolished or added on to.
How Does the Laser Scanning Process Work?
The fundamental process that occurs in laser scanning is the measurement of time required for a laser to travel to a point on the site, reflect, and return. This time is converted to a distance based on the speed of the laser. The process is repeated at an extremely high rate for millions of different points around the site.
Setting up the laser scanning mechanism
The laser mechanism is generally set up and operated as follows:
- A laser, pointed at a mirror, sits atop a stand or tripod, usually at an eye-level height. This mirror reflects the laser toward the intended target to measure the distance to a point.
- The mirror spins along a horizontal axis while the laser continuously takes measurements, meaning that points are measured everywhere from the ground level to the highest point of the structure along the laser’s path.
- The tripod itself slowly rotates from side to side, which allows the laser to capture and create a grid of all the points within its field of vision from top to bottom and side to side.
- An operator places the stand at several points around the site and repeats the process until he or she obtains positional data of all the required points on site.
The positional data recorded on site are entered into a software program, which interprets the data and produces a 3D model of all the points recorded by the laser. This model is called a point cloud, referring to a collection of millions of individual points in 3D space.
Increasingly, laser scanners are equipped with cameras that the software integrates with the positional data to create a photo-realistic model of the site. Not only does the software produce a visual representation of the site conditions, this data is interactive. The distance between any two points is measurable, and the model can be observed from any perspective.
Why Use Laser Scanning?
Laser scanning beats out traditional methods of surveying in virtually every way except initial equipment costs, and these costs continue to decrease. The process captures vastly more data and in a fraction of the time. The data is also highly reliable due to the limited human operation involved, because there is less chance for human error.
The resulting point cloud and 3D representation created by the software sets laser scanning even further apart. Although topographical data from traditional surveys can be entered into certain software programs to create a 3D model, only a limited number of data points are available. In addition, the software must interpolate between these points to fill in the gaps. With laser scanning, there are no gaps that the software must fill in, as the tens of millions of points recorded quite literally allow the software to re-create the existing site in its entirety.
The point cloud has another important use. Most building information modeling (BIM) software programs allow the user to import point clouds and build model components directly from them or in conjunction with them. This process saves time as existing conditions do not have to be modeled in the BIM software; the new structure can be modeled on top of it. Or conversely, if it is required to actually model the existing conditions in the BIM software, modeling these components from the highly accurate point cloud and photo data is an efficient process. This works nearly like tracing along the point cloud model.
Laser Scanning Saves Time and Money
As laser scanning mechanisms and BIM software become increasingly more affordable, there is no doubt that it should be the surveying method of choice for nearly all new projects. The operation of a laser scanning mechanism is a repetitive process and relatively easy to learn, meaning that specialized labor is not required, saving cost. The process hardly adds to the project timeline at all, as rarely more than a full day is required to survey even a large site. This means both time and money are saved during surveying. The vast amount of highly accurate data also helps to reduce errors throughout the life of the project, as uncertainties are reduced concerning the existing conditions of the site. Planning becomes more thorough, leading to fewer surprises that result in delays or re-works.
As construction projects increasingly employ the use of 3D models and BIM, working off a point cloud becomes very useful or even necessary. There is no question that creating detailed 3D models contributes to project efficiency and success. Building these models from reliable data on existing conditions makes them all the more effective. Laser scanning is by far the best existing method for providing such data, and is expected to be the gold standard going forward. The process is a significant leap in technology that provides numerous savings and efficiency gains due to decreased labor requirements and increased collection of precise data.