A 3D laser scanner is a survey instrument that uses a laser beam to record hundreds of thousands to millions of points on a building or site in a short time, storing them as a point cloud: a set of points with x, y and z coordinates, often supplemented with colour information from a built-in camera.
For each point the instrument measures direction and distance, and converts that into coordinates. The result is not a drawing but a three-dimensional record from which any dimension can be read afterwards — including dimensions you did not know you would need while surveying.
Types
- Terrestrial scanner on a tripod — static, highest accuracy. You scan from several positions and register those together using targets or overlap between the clouds.
- Handheld or SLAM scanner — you walk through the building with it. Considerably faster, but at lower accuracy.
- Mobile mapping — a scanner on a vehicle or drone, for sites, roads and roofs.
Applications in construction
- Measured survey of existing buildings for alteration, refurbishment and restoration, after which a 3D or BIM model is drawn within the point cloud: scan-to-BIM.
- Checking work as built against the design: floor flatness, position of openings and service penetrations, verticality of walls.
- Monitoring deformation and settlement by scanning the same structure at intervals.
- Recording historic buildings, capturing shapes a tape measure cannot.
Points to watch
- A scanner only sees what is in view. Behind a cupboard or a beam you get a shadow with no points. Clear the space as far as possible and plan enough set-up positions; going back to measure costs more than one extra station.
- Glass, mirrors and wet glossy floors produce false or missing points. Survey such surfaces conventionally where necessary.
- Accuracy is a figure quoted at a distance. Terrestrial scanners generally achieve point accuracy in the order of a few millimetres at short range; handheld scanners are clearly above that. Ask for the stated figure at the measuring distance relevant to your project.
- Agree the deliverable. A point cloud is not a drawing and can run to tens of gigabytes. Set out what you will receive: raw cloud, cleaned and registered cloud, or a worked-up 3D or BIM model. Only the last of those can be designed on directly.
- Fix the survey datum. Tie the scan to a control point and to the level datum, so later surveys and the design all sit in the same system.
Related terms
- BIM
- Digitalisation
- Geodesy
- Geomonitoring
- Building archaeology
- Section
- Datum level
Want to know more about building terms? Take a look at our knowledge base on fredsdiyplans.com.