topographical surveys, measured building surveys, drone inspections & surveys, 3d laser scanning and revit building information modelling
The 3D data obtained takes the form of a 'point cloud' which consists of millions of 3D points that define the surface of whatever is being measured. Measurements can be taken directly from the point cloud or it can be used to generate a 3D computer model.
There are several different types of laser scanner available, some can measure items such as mechanical components to an accuracy of fractions of a millimetre so precise replicas can be manufactured, others can be used to map large areas from an aircraft. A laser scanner such as the Faro Focus 3D is most commonly used for measuring buildings. The Focus3D sends out up to a million laser beams a second from a mirror that rotates vertically at high speed; the main body of the scanner slowly rotates horizontally at the same time to obtain a full 360 degree scan of everything surrounding the scanner up to 330m away.
Every laser beam sent out by the scanner bounces back to the machine which records the 3D coordinates of the point it has struck along with the reflective properties of that point. A white surface would have a higher reflective value than a dark blue surface for instance. These reflective values help us to see detail in the scan, which at this stage appears like a black and white photograph when viewed in specialist software. Some scanners (the Faro Focus3D included) also have an internal colour camera. Once the scan is completed the scanner carries out another full rotation but this time it takes a series of colour photographs. The colours from each pixel in the photographic image can then be mapped to a corresponding point in the point cloud to give it an RGB colour value in addition to its reflective value. Once this has been done the point cloud can be viewed in full colour. Scanning can be carried out in complete darkness and the reflective value of each point will still be recorded, if colour scanning is required then some form of lighting is always required.
Each scan usually takes just a few minutes, but if a greater density of points is or a higher level of precision is required then scans taking up to several hours can be taken. The density of the points in the point cloud can be set before the scan is carried out. Points can be spaced from just a few millimetres apart to pick out fine detail and become less dense the further away the object is from the scanner. The quality of the scan data can also be adjusted to alter the precision of each measured point. A greater required precision will take slightly longer to measure resulting in longer scan times.
Often many scans are needed to complete a project. The laser scanner needs to be moved around to different positions in order to get full coverage of a site or building. In order to get a complete point cloud of the whole project each individual scan needs connecting to the other scans. This is achieved by placing common targets or using overlapping geometry to tie together adjacent scans. Targets usually consist of checkerboards printed on A4 or A5 size sheets or 150mm diameter plastic spheres. The software used to process the scan data can recognise the targets automatically then use their positions to fit the individual scans together to form a unified point cloud. Other items such as flat surfaces and easily identifiable points can also be used to help fit the scans together. The process of joining the scans together is known as registration. Accurate survey instruments are usually used to fix the position the targets and to join together different parts of a project. GPS can also be used to link the targets to other coordinate systems such the Ordnance Survey network.
There are many software packages available that can be used to manipulate and model the point cloud once it is all registered together. Leading drawing and modelling program's such as AutoCAD, Revit, Vectorworks and Archicad can import point clouds to be worked on. There are powerful stand-alone programs that can cut out sections of data or drape a mesh 'skin' over the point cloud. Plug-in applications are available that allow point clouds to be used in other programs such as Rhino 3D.
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posted by steve | Feb 13, 2017
We have used Bury Associates over a number of years to survey Peel Group properties. They provide a prompt and cost effective service to us, drawing up land and building surveys of our retail development sites including the latest formats used by us and our tenants.
We have used Bury Associates on numerous occasions finding them very reliable and efficient.
Having a 3D survey for our project has been invaluable! It has allowed us to fully understand the complexities of the building from within the office, reducing site visits and queries through the design process. We have also been able to present the 3D model to the client; from existing to demolition to extension.