UNDERWATER INSPECTION
DELVING DEEP WITH 3D PHOTOGRAMMETRY BRIAN ALLEN, CHIEF EXECUTIVE AND FOUNDER OF ROVCO (PICTURED)
Photogrammetry has been around for hundreds of years, the principles of perspective and projective geometry form the basis from which photogrammetric theory was developed. Many of da Vinci’s artistic contemporaries contributed to the understanding of projective geometry from a graphical perspective.
Other scientists continued this work on projective geometry mathematically. Albrecht Duerer, in 1525, using the laws of perspective, created an instrument that could be used to create a true perspective drawing.
Although photogrammetry today employs digital imagery for measurements, the concepts go back hundreds of years and from around 1850, have followed three development cycles – terrestrial, analogue, aerial.
One of the huge challenges that faced the scientific community was how to apply these principles to gain an understanding of the underwater world. Following years of pioneering works, photogrammetric correction lenses for underwater applications were developed and have since been widely used for mapping and survey projects encompassing large geographic areas.
Fast forward several decades and the ability to generate an accurate 3D reconstruction of underwater infrastructure has become a widespread requirement for commercial, military and ocean research studies.
Subsea photogrammetry is now a technique which is quickly transforming the way the oil and gas industry assesses critical subsea assets for damage and corrosion.
Unlike many underwater scanning and mapping systems, 3D photogrammetry enables the existing conditions of
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underwater assets to be captured from millions of data points, which can then be imported into 3D modelling software to create realistic, to-scale images of the asset.
At a time when the industry is under pressure to deliver improved safety, higher operating efficiencies and reduced costs, 3D photogrammetry does all three. It unlocks the potential to produce scaled, true colour models of subsea infrastructure with millimetre accuracy in real time.
No longer do we need to rely on poor quality video with low contrast and little detail to make important decisions, we can now have full freedom of movement around an
asset as if it were frozen in time. 3D photogrammetry improves the quality of inspections, pinpointing problem areas more quickly, which in turn provides a better means of communicating this information and finding a fit for purpose solution. By taking measurements throughout the collection process we are able to constrain the model to real world dimensions. This feature allows for a multitude of additional metrics such as the distance between structure points, surface area and volume calculations, and the ability to compare past and present models to determine areas of change.
2D visualisation has been the standard approach to underwater inspection for a long time now, however as the requirement for clearer, more accurate data has increased this is no longer a reliable method for some operators. Sea life, noise and interference, combined with the limited amount of valid data available, often leads to inspection teams having to make predictions rather than base their conclusions on facts. Traditional inspection reports based on 2D data can be immense and time- consuming to analyse, replaying the video footage can take hours, resulting in an extremely costly and labour intensive operation.
3D photogrammetry systems are being developed to deliver results in near real-time generating cost savings
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