More or Less ‘Points’ for an Internal Measured Building Survey?
May 18, 2017
In July 2016, NJSR Chartered Architects were looking for a company to produce a 2D drawing and a 3D measured building model of three luxury suites of the Shangri-La Hotel at the Shard in London and Powers & Tiltman were lucky enough to get the job. The conversation quickly turned to whether we would use a Leica Total Station or a Leica P40 Scanstation to develop the elevations and models at the Renzo Piano designed landmark.
Key project deliverables included speed, cost effectiveness and producing the relevant detailed information for both models required.
The debate focused on the types of equipment available to use as both had their benefits:
Leica Robotic TCRP 1205 Total Station
Using a Leica total station creates a clean-lined internal model of a building directly to a client’s requirements. There’s no need to clear down hundreds and thousands of points created by a scanned point cloud to get to the required information (which could take days of office processing time), however it takes time on site to compile the information using a total station and a lot of potentially important information can get left behind as our surveyors pick up specific points of a façade rather than the whole facade.
Working with a total station can also hamper other building work going on around our surveyors especially if construction work needs to stop while shots are being taken.
Taking photographs of the space as an exact reference is some way to eliminating this problem but, without accurate measurements, potentially crucial information can be left frustratingly unusable.
Leica P40 Scanstation
By using a Leica P40 laser scanner we can create literally hundreds and thousands of points, resulting in a point cloud, which can create a 3D meshed surface by the triangulation of these points. The point cloud and the mesh can then be interrogated to retrieve data or ‘stripped down’ to create a simplified line drawing for design and development.
The immediate benefits of laser scanning are that the scan can be completed in a very short space of time, allowing for less site time (useful on a site on high alert to terrorism) but office processing time is longer than when using a total station. The use of point cloud means that data is captured in a measurable format and there is safety in the knowledge that eliminated information can be retrieved quickly for immediate use.
The architects would need a 2D model for their design purposes and a 3D model to comply with the building’s BIM requirements.
In addition to this, Matthew Powers foresaw other project complications:
(1) He needed to reduce the team’s time on site in order not to disrupt other contractors
(2) Gaining access to an iconic building in central London had potential security implications
(3) The cost of the congestion charge, parking and accommodation would have serious cost implications for the client if the surveyors were to stay for more than one day.
After further discussion with the client and the knowledge that point cloud could provide all the detailed information required (and, at a later date if necessary), Matthew opted to go down the scanner route and sent the team down for a day on site to complete the task.
The Shangri-La hotel sits between floors 34 and 52 of The Shard and has far reaching views to all sides. Below are two examples of the finished drawings ready for modelling by the architect from floor 39.