A reliable survey before any project decision is made
In the case of an existing building without up-to-date plans, a surveying error of just a few centimetres is enough to jeopardise a preliminary design or delay the public consultation process. 3D building scanning addresses this uncertainty by providing measurements that can be used right from the initial sketches. It replaces estimates with verifiable data, metre by metre.
How a digital survey differs from a manual survey
A 3D building scan involves capturing the geometry of a structure using laser scanning, in the form of a point cloud – that is, a set of millions of XYZ coordinates positioned in space. A 3D building survey thus contrasts with a manual survey, carried out using a laser tape measure or a 10-metre tape, measurement by measurement.
In a modern building with straight walls, the discrepancy between the two methods remains minimal. In an older building with non-straight walls, however, manual surveying leads to cumulative discrepancies from one room to the next, due to the lack of a common reference system between measurements.
The point cloud prevents this drift. Each point is linked to the same coordinate system, which makes it possible to verify retrospectively the alignment of a wall, the thickness of a slab or the ceiling height from one level to another.
How the laser scanner creates the point cloud
The building laser scanner measures the time it takes for a light beam to return after striking a surface, or the phase shift of the reflected signal. From this measurement, the device calculates a distance; this process is repeated between one and two million times per second, depending on the model.
Each position where the device stops is called a station. From a single station, the scanner captures all visible surfaces within a 360-degree field of view in a single sweep. A whole building generally requires several dozen stations, depending on its size and complexity.
The raw result of this data capture is a point cloud, prior to any processing or modelling.
The stages of a survey project
The project always begins with defining the requirements. The architect, project management team or MEP (mechanical, electrical and plumbing) consultancy work together to specify the expected deliverables, the level of detail required and the intended use of the data, prior to any on-site work.
This is followed by the preparation phase, which covers access to the premises, obtaining any available plans (where these exist), and constraints relating to the building’s occupancy, such as opening hours or the presence of tenants.
On-site data acquisition involves positioning the scanning stations to cover all surfaces, including hard-to-reach areas such as attics or service ducts.
The scans are then merged and aligned with one another to produce a single, consistent point cloud covering the entire building.
A quality control check verifies the consistency of the data before the plans or 3D model are produced. The project is completed with the delivery of the files in the formats agreed upon in advance.
What determines the accuracy of a survey
The accuracy of a survey depends first and foremost on the building’s layout. A simple structure, with right angles and constant heights, can be scanned with less uncertainty than an irregular loft or an old roof structure with multiple supports.
The visibility of surfaces plays an equally direct role. Bulky furniture, temporary cladding or stored stock can obscure parts of the surfaces to be captured, necessitating targeted additional scans.
The density of the points collected, as well as the number and positioning of the survey stations, also influence the result. The more the stations overlap, the more reliable the alignment between them becomes.
Finally, the expected level of detail, expressed as LOD (the geometric level of detail of a model), determines the required accuracy. In a typical project, the tolerance is generally between ±3 and ±5 mm, a range that narrows with a higher LOD and more advanced data processing.
Files and documents delivered following the survey
The first deliverable is the point cloud itself, exported in common formats such as E57 (an open standard) or RCP (Autodesk’s proprietary format), which can be used in most CAD (computer-aided design) and BIM (Building Information Modelling) software. This point cloud serves as a reference for all subsequent outputs.
Using this as a basis, a design consultancy can request 2D drawings in DWG format, sections and elevations, or even orthophotos – rectified and scaled images – which are useful for interpreting a façade without distortion.
The process of converting the point cloud into a structured model is known as ‘Scan to BIM’. It involves reconstructing the building’s elements (walls, slabs, services) in Revit or Archicad, to a predefined level of detail, for example LOD 200 for a sketch model or LOD 300 for a technical coordination model.
These deliverables are not automatically cumulative. A standard refurbishment project may be limited to DWG drawings, whilst a HVAC and electrical coordination project will require a full BIM model.
Adapting the level of detail to the building’s intended use
The value of a survey lies not only in the speed of on-site data capture. It lies above all in the availability, after the work is complete, of a measurable and reusable database, the level of detail of which is tailored to its actual intended use, whether that be verifying a dimension on a plan or locating a service duct during the maintenance phase.
Use cases in refurbishment, heritage and site monitoring
In a conversion project without reliable plans, the survey of the existing structure serves as the starting point for the entire project, documenting dimensions that no one can otherwise verify without destructive testing.
In a heritage building with irregular volumes, the point cloud captures deformations, out-of-plumb conditions or irregularities in the structural framework.
During construction, comparing successive scans allows progress to be monitored and any discrepancies between the actual work and the design to be identified before they become costly to rectify.
For the coordination of HVAC and plumbing installations, the point cloud serves as a common reference between trades, by comparing the planned systems with the structure as actually built.
Measurable benefits and limitations to be aware of
A digital survey ensures the reliability of measurements used in the design phase and consequently reduces the resulting errors. It also minimises the need for on-site visits once the point cloud is available to verify dimensions remotely.
Coordination between trades is generally made easier as a result, with everyone working from the same geometric basis rather than from partial and sometimes contradictory surveys. Decisions taken during the design phase are then based on verifiable data rather than on estimates.
These benefits do, however, have their limitations. A surface obscured by furniture or cladding remains invisible to the scanner, as does an inaccessible area or a closed service duct. An object in motion during the scan – such as a worker or a door opening – can also cause localised disruption to the data.
These situations can largely be anticipated when defining requirements, by identifying in advance the areas that will require a targeted supplementary survey.
Define your requirements before requesting a quote
A 3D building scan is only valuable in relation to its intended use. The level of detail and delivery formats – point cloud, DWG, Revit or Archicad model at a given LOD – must be defined before the work begins, not afterwards, which ensures that the survey produces exactly the files required.