From UAV to BIM – How UAV data fits into the Scan to BIM work flow

We are moving towards a world where 3D is the expected format, whether it is in games, the cinema or indeed the world of construction and surveying.  For the next generation to enter the construction workforce this will be the new normal. However, there is no doubt that its adoption in a commercial sense is being hastened in the construction industry by the shift towards the adoption of BIM(Building Information Modelling).  The embracing of information rich BIM technologies will be a catalyst for new more efficient ways of working at all stages of the building project life-cycle.

Major projects all require multidisciplinary engineering infrastructure, from design & project management to enabling works, site clearance, remediation and environmental impact assessment and so on. These projects will consequently benefit from being information intelligent with this information being able to be viewed holistically. To be information rich requires the input of large amounts of spatially accurate data all through the project. 

Contrast this with the traditional method of surveying which involves capturing one point at a time; a process which can be slow, predisposed to human error and necessarily selective. Increasingly though the requirement is for a faster process with visual feedback. Given as mentioned above the workforce is changing and increasingly comfortable with a 3D in-line environment it is not unreasonable to expect modern surveying techniques to deliver a similar scenario.

The availability of 3D data is not just a technological advancement in surveying techniques but it delivers a fundamental shift in how survey data can be used. In a nutshell it brings the real world to the desktop and this means that (in addition to saving time and money on the survey process) 3D data provides the tools to appraise existing conditions, monitor construction progress, carry out structural assessments, record as-built conditions and generally enhance asset management.

Delivery of an information rich environment can be achieved through ‘Scan to BIM’ a process which takes scan data, traditionally from laser scanners and turns it into solid surface models using automated software.  The data is in the main captured via a laser scanner which is a fantastic tool for collecting point cloud data, providing incredible accuracies and detail. The main drawback with laser scanners is the static nature in which they collect data. Laser scanners collect points by spinning lasers beams from an accurately known location and measuring the time taken for the light to reflect back to the scanner. Since light can only travel in a straight line, if there are any objects in between the scanner and the target, a shadow is cast causing holes in the data. To overcome this limitation the scanner has to be moved around on site to ensure all the details are captured. Selecting suitable scanner positions requires a lot of experience and skill, and each time the unit is moved, a lot of time is taken setting it up. Even with the most skilled users there are still surfaces, such as roofs, which cannot be captured.

UAVs are an alternative solution which readily addresses the need to capture inaccessible areas such as roofs. UAVs are best utilised when scanning the externals of buildings due to their speed. This data can then be merged with for example, laser scan data collected for the building internals to produce a complete point cloud of the whole building, inside and out.

Unlike laser scanners, UAVs are able to scan roof tops meaning that a full and complete data set can now be achieved, and due to their mobile nature they suffer much less from shadowing from nearby objects. As well as producing point clouds a UAV survey also provides hundreds, if not thousands of images of a building from every angle providing a much greater depth of information than could be achieved from ground based scanning techniques. With improvements in positioning accuracies, developments with software and a continual improvement in understanding from drone operators, point accuracies have now been demonstrated and validated down to just a few millimetres. A UAV survey will provide clients with accurate point cloud data which can be processed and imported into BIM software such as Autodesk Revit & Archicad to create an intelligent 3D model.

It should be noted that achieving high data tolerances requires skilled operators who know how to capture the data, understand surveying principles to generate accurate points and who have the experience of operating in challenging environments. This is equally true however with all developments in surveying or indeed more broadly whereby a balance has to be found between technology and employee capability.

With data from both internal and external sources the survey workflow must therefore use a multi-threaded approach to provide an economic solution to BIM modelling. For example, terrestrial laser scanning can be used to capture the inside of a building, a UAV can be used to capture photogrammetry that can be processed to give data on the externals and of the surrounding area and mobile laser-scanning can be used to capture engineering grade information about access roads.  Integrating all of the information from different sources enables a complete representation of a building that can be used for a variety of purposes including redesign, visualization of the building inside and out for prospective customers and as a historical record.

At each stage of the construction process, UAV Scan to BIM can be used for verification as it is a quick and effective tool for checking the real world against design plans. Any damage or deformation in building structures or roofs can easily be modelled using UAVs and can be easily integrated into BIM workflows.

Below is the “UAV Scan to BIM” workflow:

 Building Information Models are on the way to providing the depth of information that tomorrow’s clients will come to expect and are undoubtedly much richer than the previous 2D representations. There is a far higher density of knowledge captured and layered with BIM. What the UAV can do is essentially capture reality and transfer it to the desktop to be manipulated in endless ways. This is only possible because the survey is capturing millions of points of data where as traditional methods are only able to capture at most a few thousand.

This is going to be a very exciting and transformational era; there will be significant changes in the way buildings are managed starting from design, right the way through the building’s lifecycle. Moving from traditional surveying and the data that provides to a radically different approach with its wealth of data may feel like a brave move currently but there is a point in the not too distant future when UAV surveys and laser scans will be the norm.

The advantages of UAV scans are already available here and now and additionally offer a low cost advantage meaning the only barriers to adoption really are those who fear the process of change.

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