UNDET Enhances Accuracy and Reliability of Construction Retrofit Workflow

A Canadian construction company needed to extract highly accurate building geometry from existing residential structures to fabricate new exterior wall panels. With no background in 3D scanning, the company sought a point cloud modeling solution compatible with its SketchUp design package. 

Butterwick Projects Ltd. is a net-zero construction firm based in Edmonton, Alberta, Canada, that is currently engaged in retro-fitting townhomes with prefabricated, energy-efficient wall panels. To design and create exterior panels that fit perfectly onto the existing buildings, Butterwick must capture precise as-built geometries of the outside walls, including dimensions, angles, curves, and out-of-plumb corners.

“These buildings aren’t square or straight, [and] we have to know what’s there to design the panels. If we make panels in the factory and they don’t fit, construction stops and it’s a disaster. We waste time and money.”

Peter Amerongen, Butterwick Managing Partner

On the first building, a test for a 51-townhome retro-fit project, the firm used tape measures and levels to collect the desired geometric details. However, this manual process was time consuming and required extensive checking and rechecking to avoid mistakes and inaccuracies, especially in wall corners and window frames.

Butterwick’s intention was always to utilize digital data capture for the remaining buildings. For that to work they needed a way to accurately derive building geometry from 3D point clouds. UNDET, looked to be the perfect answer.

A local surveyor scanned the next building with a Leica BLK 360 stationary laser scanner and used surveyed targets on the buildings to improve the scan registration. He sent the resulting .e57 file to Amerongen.

Digital Capture using a LEICA BLK360 Laser Scanner

Amerongen used the UNDET tutorial resources to learn the software and extract the necessary building geometry, especially window and door locations.

To determine if the result was accurate enough for panel design, he took dozens of tape measurements from the building to compare with the UNDET extraction. Most were within the hoped for 5 to 6 mm. When he double checked the bigger errors, it turned out it was the tape measurements that were wrong. The realization that while a digital scan might have an error of a few millimeters, it would never be off by a foot or on the wrong side of the building gave him the confidence to commission the scan of the rest of the 15-building complex.

Once the wall geometry is extracted by UNDET, he can begin drawing the new panels in SketchUp. The 3D extraction has to be precise because he relies on the existing wall geometry as the base layer to draw the panel details.

Amerongen performs much of his work in UNDET using the Automatic Feature Extraction tools. He simply clicks on any point on an exterior wall, and the software automatically extracts the required wall plane. Two clicks are all it takes for UNDET to create a line representing the exact corner geometry in SketchUp. There are several feature extraction tools depending on the exact task at hand.  

There is always some interpretation involved in converting a bunch of fuzzy points to planar geometry. This can be a bit nerve wracking due to the importance of wall geometry being measured correctly to ensure a correct fit for the prefab panels. UNDET has several features that inspire confidence. One is that there are several ways of increasing the visible point cloud density. You can either shrink the clipping box and the software will automatically display a higher point density – without sacrificing speed and performance or you increase visibility in a bigger clipping box with a slider (and put up with somewhat slower performance.) The other is a new tool that gives immediate visual feedback on how well the Sketchup planes align with the points they were extracted from – a great confidence booster.

“There were high fives all around. The panels fit beautifully … It was a triumph. We had given ourselves a 10mm allowance for adjustment but hardly needed it. UNDET solved our point cloud extraction problem brilliantly … and the technical support is great. I really feel like the guys there have my back. If I email them with a problem, I get a response right away.”

Peter Amerongen, Butterwick Managing Partner