Capturing visual construction data, photogrammetry & 3D scanning.
Collection of data relating to objects, buildings or the general site is important for visualisation of design ideas and accurate execution during construction. Two imaging technologies that can be employed to collect this data are photogrammetry and (Three-Dimensional) 3D laser scanning.
Photogrammetry
Photogrammetry is the use of an array of photographs (visual representations) taken with an overlap to measure distances and angles of objects when surveying the general environment. Information of objects is captured from different vantage points by satellites or taken within a close range by using a smart phone (within the relevant phone applications), digital cameras and Unmanned Aerial Vehicles (UAVs) like drones. Images once generated, are then fed into photogrammetry programs like Meshroom and Site Scan that triangulate this information and rebuild the form surveyed in a digital version- either as a 2D digital image, 3D model, or point cloud. This conversion employs use of optics, projective geometry, remote sensing and computer vision, of which the first two can be traced back to 1492 with Leonardo da Vinci’s explorations of optics and perspectives. This science has since expanded to include analysis of digital images, radiated acoustics, laser scanning measurements, and magnetic patterns as well.
Metric photogrammetry as a process facilitates high accuracy in establishing exact distances, angles, areas, volumes, elevations, and sizes and shapes of objects. This can be used in land survey to analyse the potential site- its grade and slope, note exact details of existing structures and any limiting elements to create a very accurate scaled site plan for design implementation. Streetscapes can be easily and accurately documented for urban planning research and design purposes by employing photogrammetry. Interpretative photogrammetry comes into play as it involves systematic analysis of the significance of images captured. Selected high quality images are captured by remote sensing instruments in moving vehicles for accurate reconstruction in the software.
Google Maps is a familiar platform that succeeds in using this tool, using satellites.
3D Laser Scanning
Laser scanning, on the other hand, employs targeted laser beams that measure the distances and angles from the point of projection. As the equipment is mounted on a tripod, it works well for a small area (as opposed to photogrammetry).
It can be employed to take site measurements for 3d modeling of the potential site (similar to photogrammetry), infrastructure and other physical site elements. These are documented accurately for mapping and design thereafter. Interior surveys can be done through this process, which is useful in renovating old structures whose architectural drawings do not exist. Point cloud data generated from the software can be imported into design software thereafter developing as-built drawings. Additionally, no future site visits are necessary as additional measurements can be taken from the model. Other specialists involved in the project can easily access this common model developed for input with the aid of cloud integration.
3D laser scanning, capable of capturing all details, can highlight potential errors that would otherwise be overlooked through a manual survey. Site inspections and reports are accurately developed and errors mitigated that would cost time and money to the client especially relating to conflict in building services. Another example is the use of the laser scanner to determine slab levelness. Employed to monitor construction progress, 3D laser scanning can also review the contractor’s performance. Scans are developed from embedded sensors around site and reviewed at specified time intervals.
This technology can also be used in the documentation of historical landmarks and conservation of cultural heritage through digital representations of the same, without which would be lost. Monuments of historical significance are recreated and the models rendered to have real world textures and appearances. Virtual walkthrough tours within the model, gives one a full perspective and an overall immersive experience with an unmatched experience.
There are several advantages of using photogrammetry and 3D laser scanning and the construction industry stands to benefit greatly from the speed and accuracy of all the valuable data collected by these technologies over traditional surveying methods.
