By James Hayes, Principal, If Then Architecture Inc.
Though the uptake and use of Terrestrial Laser Scanning (TLS) and other digitization technologies within the AEC community still varies greatly, we at If Then Architecture Inc. (ITA) work to implement solutions for any project stakeholder regardless of their technical capabilities. We find that architects and engineers, especially those immersed in BIM, are more likely to have an understanding of the value of these technologies and increasingly see them as fundamental when a project involves an existing building. Other stakeholders who are less invested in digital technologies tend to be less aware of these technologies. General contractors in our experience are most likely to use these technologies when required by a project specification. Building trades and building owners that spend their days outside of the BIM bubble are the least likely to be seeking them and may not have heard of the technologies at all.
These observations align with different ways architects and engineers work on the one hand and the way general contractors and their sub- trades work on the other. Consultants tend to work in the digital world of design, while contractors and building trades in the physical world of the construction site.
Nonetheless, even for those in the know, vague marketing terms like “reality capture” obfuscate and sometimes exaggerate the capabilities of these technologies. (Perhaps we should all earn an advanced degree in philosophy in order to gain a grasp of the true nature of reality, before we attempt to capture it). A more helpful, albeit less provocative, term is simply “Building Documentation”. Building Documentation removes the focus from any specific technology, placing it on the building and what particular information is sought.
Prioritizing “information” over technology is not a disavowal of the latest and greatest technologies. At ITA, we use a suite of techniques and technologies – terrestrial laser scanners, hand-held scanners, SLAM, total stations, photography and photogrammetry using DSLRs and UAVs – but how we proceed for any given project is based on the deliverables required. The ultimate deliverables might be 2D drawings or a digitally-fabricated component.
Among these various building documentation technologies, there are two defining characteristics – measurement and visualization. Some technologies are more suited for measurement, while others are more suited for visualization. As an example, a total station takes very accurate measurements, but does not create a dataset suited to visualization. On the other hand, a 360o camera that creates panoramic photographs is great for visualizing spaces but not for measuring distances. In between these two extremes is a spectrum of technologies and combinations of technologies that both measure and visualize. Photogrammetry and TLS are examples. At ITA, we place an emphasis on maintaining the highest level of measurement accuracy that is practical, in combination with the highest fidelity visualization.
The most common building documentation projects that ITA completes are, not surprisingly, for renovations or rehabilitation of existing buildings. The typical parameters for these kinds of projects are a requirement for documentation of as-found conditions because there is scarce, out-of-date, or no existing documentation, prior to or at the early stages of design, in order to provide a baseline level of data to inform architects and engineers in their design work. The data is intended to provide a metrically accurate, overall representation of a building in its entirety. A recent example is Hart House at the University of Toronto (images at right).
Projects that are less common, though are increasing in frequency, are documentation during construction to facilitate fabrication. Whereas the goal of documenting existing buildings is to create a comprehensive overview, the goal of documenting for fabrication is to provide precise information about very specific locations. Typical parameters for these projects are a requirement for a high level of precision, taking measurements by hand is not practical or possible, and the building or element of the building being constructed is geometrically complex.
The motivation for documenting during construction for the following example projects is the “gap” – the difference between the information provided by contract documents, and what has actually been built. The gap occurs over the course of a construction project multiple times when one trade completes their work and another trade follows, using the previous trade’s work as a substrate for their own. On typical construction projects and with experienced trades, the “gap” can be overcome by accurate site measurements and/ or a trial and error of cutting and fitting. However, when the design and other project parameters are atypical, the “gap” can be problematic and a costly challenge to overcome.
The Visitor Welcome Centre on Parliament Hill (by IBI Group and Moriyama & Teshima Architects) and the Canada Science and Technology Museum (by NORR) in Ottawa are examples of this kind of situation. For both, the entrances are key elements with unique geometry. In the case of the VWC, the entrance façade is itself the only exterior portion of the building. The facade consists of a stone wall that follows the curve of the Vaux Wall and is punctuated by two large stone arches one of which is doubly-curved. The wall and arches are built over a cast-in-place concrete structure.
At the time of construction, it was imperative to have accurate measurements of the concrete structure to enable RJW Stonemasons to complete their work of building the stone wall and arches. The doubly curved arch was expected to be especially difficult to measure using traditional means.
ITA was tasked by RJW Stonemasons with scanning the concrete structure of the entrance to ensure timely and accurate measurements. A Leica P40 was used to scan at a resolution of 1.2mm @10m. Using TLS in place of traditional means significantly reduced the time on site for measurements. The scan data further enabled RJW to virtually construct the arches and wall digitally.
The dynamic entrance of the Canada Science and Technology Museum features enormous LED panels covering angled walls and soffit which form the entrance canopy. Similar to the VWC, during construction the “gap” was manifested when one building trade was required to build over the previous trade’s work with atypical geometry. In this case the cladding was the large LED panels rather than the stone of the VWC. The scale of the canopy and angular geometry made acquiring measurements for the panel installation by hand difficult at best. The importance of acquiring accurate measurements of the surfaces was underlined by the fact that the LED panels would be manufactured off-site with essentially no adjustment to be made on site. ITA used TLS to scan the angular walls and soffit. From the point cloud data, ITA modeled the surfaces to which the LED panels would be attached and provided it to the LED panel manufacturer.
Documentation for fabrication is not restricted to large institutional projects. As an example, ITA was asked to document a spiral stair under construction in a private residence, to enable fabrication of the curved glass panels of the guardrails. The laminated timber stringers with stainless cylindrical standoffs were installed in the residence, but accurate measurements that would inform the fabrication of the glass guardrails were challenging. In order to accurately plan the glass guards both the location of the standoffs and the surface of the stringers needed to be measured. Afterscanningandextractingthe individual standoff locations, ITA modeled the glass panels using the point clouds of the stringers as a guide. The glass panels were “unfolded” and the resultant geometry was provided to the glass manufacturer in Europe. The glass was fabricated and installed without the need for modification.
Deep energy or net-zero energy retrofits are the process of modifying existing buildings to significantly increase their energy efficiency. They are a project type that is only going to increase in frequency as Canada’s response to climate change addresses the significant percentage of our carbon footprint contributed by existing buildings. Natural Resources Canada’s Prefabricated Exterior Energy Retrofit, or, PEER project, is one such facet of the federal government’s response, is a research initiative in collaboration with industry partners to develop strategies for deep energy retrofits. “Developing, testing and validating innovative prefabricated building envelope technologies for retrofitting existing Canadian homes from the exterior.” Prefabricated building panels are applied to the exterior of the building leaving the interiors untouched. As such, acquiring accurate measurements of the building exterior is critical.
ITA’s role as an industry partner is twofold. The first is to provide documentation services for the buildings chosen as test sites for prototype panel installations. This was completed using a combination of total station, TLS and terrestrial and aerial photogrammetry. The raw site data was then transformed into drawings specifically for the manufacture of the prototype panels. The panels will be installed in early 2021.
The second aspect is to establish workflows for both the fieldwork and extraction of the critical measurements from the field-acquired data. Since the intent of PEER is to apply the findings of the research across Canada, accommodation must be made for geographic locations where some of the documentation technologies will be available and others will not. Therefore part of developing the workflows is also to develop an understanding of the strengths and shortcomings of the data from the various combinations of techniques and technologies specific to the exterior retrofit application.
The challenge of the documentation process for PEER is the requirement for accurate overall dimensions because of the large size of the panels, as well as accurate measurements of door and window openings that will be built into the panels. Measurement and construction tolerances are intended to be less than 1cm.
Documentation during construction to facilitate fabrication can provide benefits to most construction projects, but is not critical for the success of straightforward, run-of-the-mill construction. However, the most significant benefits can be seen in those projects where off-site prefabrication or complex geometry exacerbates the “gap” between the design intent of contract documents and the physical realities of construction. When presented with atypical designs or challenging geometry, trades may price work based on a trial-and-error strategy of multiple installations before finding the right fit. Having accurate measurements and comprehensive visualizations can at the least save material waste by avoiding these kinds of strategies. In the best cases, accurate measurements and comprehensive visualizations lead to better quality workmanship, tighter construction tolerances, and compressed timelines via off-site prefabrication.