TopoCrew's laser scanning supported a major tunnel reconstruction in Central London, minimised traffic disruption, and provided FM Conway with a reusable 3d point cloud for future monitoring and maintenance.
Project Snapshot
Project type: Laser scanning and extraction from point cloud
Client: FM Conway
Project area: 16,077 sqm
Borough: City of Westminster, London
Location: Knightsbridge – Piccadilly
Instruments: Leica RTC360 Laser Scanner + Leica Total Station
Deliverables: Road Marking map – Full 3D topographical map with DTM
Introduction
Our client, FM Conway, required an accurate and detailed topographical map for precise road marking placement and future resurfacing works in London’s Piccadilly Tunnels.
Tunnels are always challenging to map. Closing them is problematic because traffic cannot easily bypass them, and building and maintaining a precise ground control point network requires careful planning and execution. To minimise traffic management time, the best practice is to scan a tunnel, creating a digital twin—a virtual replica—on which we can perform mapping or inspection tasks remotely from our office. Our team conducted this scanning for the Piccadilly Underpass tunnels, a vital part of London’s road infrastructure. With the digital twin—a 'snapshot' of the tunnel at a given time—we can utilise this data for multiple future projects, ensuring the proper operation and safety in London’s busiest district.
Our primary objective was to create an accurate and detailed topographical map that FM Conway could use for precise road marking placement and future resurfacing works.
Project Objectives and Challenges
This project involved two phases, both derived from the same laser scan. We conducted the scan in 2023, primarily for road marking extraction. As the tunnel has not changed since then, we utilised the same point cloud for full topographical extraction this time. This approach saved time on site because the complete site data was already accessible from our office. As always, our topographical maps are cross-checked on site after the office work is done to ensure the highest accuracy for our clients. If needed, we can carry out additional scans and attach these to the original point cloud.
The real challenge was the tunnel itself. While establishing the triangulated station and reference point network was straightforward due to the tunnel’s linear nature, the extraction process was difficult. The tunnel had many wet and water-covered areas, where laser intensity can drop, making extraction significantly harder.
In standard cases, photos from the scanner can be used to spot details or identify manholes, but in tunnels, the image quality is inadequate due to the dark environment. This makes it impossible to properly colourise the point cloud based on the photos. In these cases, laser intensity can be used, but due to the presence of water it also becomes a bottleneck. Water surfaces can act as mirrors or simply absorb the laser beam. This should be considered by anyone utilising laser scanners.
Adverse conditions such as rain, wet surfaces, fog, and snow can degrade point cloud quality. These problems can be challenging, but TopoCrew’s engineering team is trained for such cases, with over 30,000 working hours of experience and numerous collected laser scanning datasets.
TopoCrew’s Approach
As always, we established our own station and reference point network with a density of 40 metres to ensure a sufficient number of control points for scanning. Ensuring the reference network’s stability is crucial to address all accuracy concerns, as the reference network’s reliability is the key factor for the point cloud quality. Our team always cross-checks the triangulation independently to mitigate any possible errors in advance.
Initially, we planned to use a mobile scanner for the task to avoid the need for a road closure. However, since traffic management had already been arranged for planned maintenance works, we scheduled our survey accordingly. The point cloud was clean from noise—false points due to moving cars and people. Our team utilised the TSGS—TopoCrew’s custom GIS workflow, which ensures compatibility with both CAD and GIS systems—for the extraction.
Even though the second project came a year later, we used the same point cloud and techniques to extract the content the client requested. Having a point cloud from a site is beneficial, as the client can request more information from the site without the need for on-site work. In this particular case, traffic management is a difficult and expensive process, so avoiding it can lead to major time and cost savings for the client. That is why we always prefer the laser scanning approach whenever possible, because a large amount of information is available in the cloud, which might not even be considered during the initial order but can be very useful later on.
Results and Project Impact
A highly detailed and accurate map is essential for a refurbishment like this, and the engineers at FM Conway can trust us with this survey as well.
The resulting maps were used by FM Conway to refurbish the road painting and carry out a major reconstruction. As the point cloud is available for us and the client, it can be used in future projects, such as monitoring or extracting additional information. For example, if we scan the tunnel again in three years, we can compare it with the previous scan to detect any possible movement and deformation. We can measure how many square metres of wall tiles must be replaced or how many kilometres of cable tray have been installed inside the tunnel. Reusing a point cloud—a digital twin—will become part of standard planning processes and enables precise validation of road and highway design.
The refurbishment work has already been partly carried out, with some parts of the road receiving a fresh asphalt layer, and more work is to follow based on our maps.
Conclusion
Once we scan the site, we can reuse the digital twin data in the future and extract the required information in the right format. This eliminates costly and time consuming resurveys and delivers substantial long-term savings to our clients. We always verify and cross-check our topographical maps on-site for complete accuracy.
FM Conway is already using the topographical map we created. They can also use the point cloud in a BIM system, as well as to track maintenance costs, minimise disruptions, plan future works inside the tunnel, and ensure optimal resource allocation.
TopoCrew’s detailed methodology and expertise in laser scanning have consistently provided our clients with reliable and actionable data. We encourage all our current and future clients to contact us to learn about the full potential of digital twins and laser scanning technology for their projects.