Why modeling point clouds alone causes error
I remember the experience of seeing my first laser scan point cloud. I was at a conference in the early 2000’s. A strange instrument was set up on a survey tripod in a vendor’s booth in the exhibit hall. The technician manning the device also had a computer hard wired to it. As I stopped to investigate, I thought, “What in the world is this?” Gazing at his screen I watched with amazement at what I was seeing. There was a 3-dimensional image of the truss system holding up the exhibit hall’s roof rotating around on the monitor. “Wow! That’s crazy,” I thought. I asked, “what is this thing?” He said, “it’s a 3D laser scanner.” I asked what it cost, and he told me about $250,000. I thought, that is as much as a house. I guess I’ll never own one of those.
Fast forward to today. I now own multiple laser scanners. The prices have come way down as the prices of homes have gone way up. I probably should have bought more homes, ha! Point clouds aren’t too smart since, after all, they are only just a bunch of measured points. One must interpret them to understand what they represent. One of the more popular workflows to represent existing conditions is referred to as ‘scan-to-BIM.’ A common mistake inexperienced modelers often make when creating a BIM from scan data is they trace the points without understanding what they are modeling. Upon further investigation, a shaft drawn in a place that makes no sense may end up actually being a structural element. When this occurs, it is a dead giveaway the modeler was only modeling points without first taking time to understanding what is going on in the space they are trying to represent.
The best way to avoid these types of mistakes is to first study the space. Try to understand the design intent, what elements are present, what the purpose and function of each item in the scene is for. If record drawings are available, review them first before beginning your BIM modeling effort. Look at any available photos, especially 360° imagery. Most of the time, buildings and building systems are constructed in a way that makes sense if you can determine the intent. Remember, don’t model points, model the building elements they represent.
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