Traditional surveying creates an imaginary line between two points. It’s a way of creating a grid that can help locate and define existing terrain and structures. It’s simple, but it’s artificial. Think about how the eye maps terrain and objects. The eye also sees in straight lines, but does so continuously—like a sheet draped over everything in range.
What if we could imitate that same behavior with light? Enter: LiDAR
LiDAR (light + radar) is a laser scanning technology developed as the natural successor to traditional surveying. Traditional surveying is point to point, as is LiDAR. However, LiDAR can scan up to 50,000 points every second. From a source camera, a laser is projected and the bounced beam’s intensity (reflectivity) is measured, which in turn determines a given point’s distance from the source. Each of these reflections creates a point, and by moving the camera and aligning the overlapping points, a “cloud” can be formed which begins to mimic 3-dimensional space. The laser has a reception range of nearly 900’ and is accurate up to 150’. The resulting point cloud has a 1/8” tolerance.
In-the-field scanning consists of simply positioning and re-positioning the laser camera in strategic points to accurately capture a space, similar to walking through a building. Often attached to the laser is a regular camera which takes panorama images at each point to help illustrate the point cloud once it is formed. This collection process results in large amounts of data–literally gigabytes more than can be obtained with traditional surveying.
The next step of the process happens on the computer. The point clouds are run through software which identifies common/overlapping points in order to stitch data from each camera location together into a continuous model. Various components like pipes can be designated as such and the software can then interpolate them as cylindrical. As an optional extension, the panoramic photographs can be assigned values based on their color and this integrated into the point cloud, creating a virtual space.
So is it worth it? The answer largely depends on the desired goal. While it only takes 20 minutes to dimension a typical room, approximately each hour of scanning requires an hour of in-office processing to produce CAD documents. The ratio goes up to 1:10 for 3-D modelling. Thus the time savings is not significant, and the cost savings can vary. What is clear though is the amount of data generated. A fully 3-D scanned building virtually eliminates the need for multiple field visits. And the level of accuracy far surpasses traditional surveying.
Laser scanning can also begin to capture details traditional scanning would miss, such as complex heights and wall anomalies. For example, the Historic Odd Fellows Hall, which CRSA helped relocate to a new site, was actually an entire foot out of alignment from top to bottom. We assume all things in buildings are square, but only a continuous scan can truly verify if conditions at 1’ of elevation match conditions at 5’.
Special thanks to our friends at McNeil Engineering for their pioneering work in LiDAR surveying. Learn more at www.mcneilengineering.com