How a Danish surveying consultancy uses advanced scanning technology to support affordable housing.
By John Stenmark
The good news was that Danish surveying consultancy LE34 won a bid to scan thousands of housing flats. The bad news: Traditional scanning workflows would involve too much time per flat. In order to succeed, LE34 needed to radically reduce the time and cost both on-site and in the office. The solution involved creating workflows to leverage a self-calibrating scanning system with automated cloud registration that cut field acquisition time and nearly eliminated manual office processing. Thousands of scans later—and counting—their new system and the process it has enabled, continues to exceed expectations.
Thousands of Flats
Boligforeningen AAB is a non-profit that administers nearly 20,000 homes and flats in the Greater Copenhagen area, managing and leasing these to achieve sustainability and affordable-housing goals. AAB issued an EU tender to scan thousands of these units to streamline the process of tenant changes. By using 3D models of units, AAB could reduce estimating costs for unit refurbishment prior to new tenancy to a single site meeting.
LE34, a prominent multidisciplinary Danish surveying consultancy, sought to bid on the project but Engineering Surveying Director Anders Nygaard Møller and his colleague, Chartered Surveyor Richard Lindquist Capion, realized that conventional scanning workflows might not provide the competitive edge needed to satisfy the tender.
AAB, required 3D models in Revit for each type of flat, along with the offices, shops, basements and stairwells in each housing block. To turn the point clouds that LE34 created from the scans into the finished 3D models, LE34 tapped the expertise of Ramboll, a leading global engineering, architecture, and consultancy company. Capion said “With a 3D model, AAB can estimate the quantities of painting, carpet, piping, etc., that need to be replaced or repaired before the next tenant moves in. The property manager, tenant, and contractors can all view and measure in the 3D model. With one site visit, AAB and the departing tenant can calculate quantities, send these to the contractors and determine how much of their deposit they get back. Our job is to scan the flats, merge the point clouds, perform QA & QC per the client’s specifications, and export the clouds for each flat into Autodesk ReCap for Ramboll to create the Revit models.” LE34 was looking to automate the processes.
Møller and Capion were intrigued by a recent demonstration of a new 3D laser scanner, the Trimble X7, and worked with Trimble distributor Geoteam A/S to acquire their first X7 and get up to speed on operations. “It was fast enough – 500,000 points per second,” said Møller. “But what really stood out was the automated cloud-to-cloud registration in the field and on the tablet. The on-site results looked to be as good as what we could do registering the point clouds in the office. This eliminates much of the office time for processing the scans, essentially cutting our time for each site in half.”
Scanning Flats Becomes Flat Simple
The LE34 team notes several features that have enabled them to scan up to 10 flats per day. Unlike other scanners they have used, notes Møller, the X7’s base is the same kind of compensator unit used on high-end total stations. “It does a self-calibration in a few seconds. So it is level, we don’t have to worry about that, no errors in that,” he said. “It comes with a light carbon fiber tripod, and we can just pick up the whole thing and move it between scan stations.”
Henrik Kjærsgaard Christensen, a LE34 Chartered Surveyor who oversaw much of the scanning, was impressed by the system’s simplicity. “You do 15-20 quick scans of each flat, shop, or office and the scans register automatically. It is easy to train someone to operate and look for any issues. We can do this in the field without having to do the registration in the office later. If needed, we could even hire surveying students to do the scanning,” said Christensen.
Capion explains the in-field QC process. “You register scans as you import each from the scanner into the tablet; this is via a WiFi connection, so it is mostly finished before you begin the next scan. While it is doing the next scan, only a few minutes each, the Perspective software is doing the cloud registrations. You can see if there were any problems with the scans or registrations; if not, there is a refinement step that performs a least squares adjustment of the registrations.”
The scanning crew does not need to do much prep before scanning, except to cover up mirrors and close curtains and blinds to remove reflections, per the contract specifications. Furniture and fixtures in the flats were not a problem. LE34 sent a short video of each room to Ramboll along with the point clouds so they could identify and connect features partially obscured by objects in each room. The scanning and cloud merge for each flat is completed on-site in about 45 minutes, including the time to move to the next unit in the same housing block.
“We did not need to use the scanner globe targets like those we use with conventional scanners, as the registration is automated,” said Møller. “But the contract called for us to use them. This was OK because we could use the globes as part of our QC process.” In the office, LE34 developed scripts to open Trimble RealWorks, check the registration quality, provide a report of the results, and export the data to Revit. They added a script to make use of the globes, detect them in the point clouds, and check the relative integrity. “The contract called for 2mm accuracy on the globes and 4mm on the points cloud registrations,” said Møller. “There were only a few times we did not meet this and then we would adjust the registration in RealWorks. Usually we were between 1mm and 2.5mm.”
LE34 has produced almost 60,000 scans, encompassing thousands of sites with their first X7. It is almost unheard of for legacy scanners to get this much use without having to be sent in for calibration. “We may have a scanner out of service for two or three weeks for calibration, and this can be quite costly over the life of a scanner,” said Capion. “With the X7 we do not have to worry about this.”
LE34 keeps long-range scanners, like the Trimble TX8, in their inventory for large-scale outdoor projects, using target globes and doing cloud registrations in the office in RealWorks. But their success with the X7 has prompted them to purchase four more, and they are beginning to test out the units on different types of projects. As Møller reiterates, “Being able to register and check the cloud in the field and eliminate much of the office work has great potential.”