Alasdair Kirkwood, commercial director at L&M Survey Services, looks at why HDR (High Dynamic Range) camera technology has the ability to transform survey data inputted into the BIM process
HDR (High Dynamic Range) cameras produce images that are revolutionary in terms of quality and content, compared to those carried out using existing LDR (Low Dynamic Range) cameras.
A shortcoming with LDR technology over the last few decades has been that it has struggled to keep pace with data requirements, specifically the need for precise, accurate information for inputting into the BIM process. Take just one example; LDR cameras have difficulty capturing scenes that contain very light and very dark areas.
What tended to happen was that the camera was adjusted so that it could capture either the dark or the light areas, but not both. For instance, if the interior of a building on site was being photographed, everything inside might appear dull and underexposed whilst a near perfect view through the window was captured. Alternatively, the inside of the building might have the right exposure levels — albeit with darker areas on the unlit corners — but with overexposure in the window appearing as a bright white mass.
For everyday images this may not necessarily be an issue, but with visual asset management in the surveying sector, under and over exposure can result in loss of vital data. For example, the light areas in the window or the dark corners in the room could be hiding a critical service, fire stop aperture or issue with the masonry. The problem can also be exacerbated in specialist surveying environments such as rail where it is common to have very light and dark areas, such as those in underground works or derelict structures that may not have services connected. Alternatively, surveys may need to be carried out at night, in the case of rail, meaning LDR cameras require cumbersome lighting that can also present health and safety issues.
The recent uptake of High Dynamic Range (HDR) cameras in the surveying sector is helping to address the shortcomings of traditional Low Dynamic Range (LDR) technology. The basic premise of HDR cameras is fairly straightforward; the camera captures several versions of the same image using different levels of exposure. The technology then blends these images together, creating an amalgamation, which means that it includes different exposures all in the one, final image.
If we again take the scenario of the internal survey of a building on site, the HDR camera would take a number of images at different exposure levels and then combine these so that the inside of the room was at optimal exposure – even the dark corners – whilst ensuring correct exposure on the window, avoiding it appearing as a whiteout area. The end result is an image that is close to, or sometimes better than, what the human eye sees.
Applying the technique to visual asset surveys therefore has the potential to revolutionise the way in which data is captured, presented and used. That has huge implications for BIM because it means better quality information is inputted into the BIM schedule from the start of the project. The real benefit of commissioning surveys using HDR images is that they contain pixels with a much greater range of light and colour, which greatly improves the overall quality of visual surveys — reproducing real-world appearance and an ability to ‘see in the dark’.
The practical uses of HDR technology are far reaching and range from an ability to identify anomalies that the human eye could miss, for example, hairline cracks in substrate, through to completing detailed surveys in dark, hard to reach places, such as the rail tunnel on page 50. All that is aside from HDR providing better quality and more usable information for BIM.
HDR for BIM
Within the area of BIM, HDR camera technology is able to provide 3D documentation, GIS and geomatic information at every stage of the life cycle of the asset. This extends from feasibility and topographic surveys, measured building surveys, scan-to-BIM, as-built modelling, point cloud management and distribution to as built-data collection.
The data captured by HDR integrates into all the major BIM compliant tools, such as Revit and Bentley’s suite of infrastructure design products. It also provides hands-on help with BIM implementation, workflow, documentation management, clash detection and modelling, asset management and knowledge management. Essentially, HDR creates accurate, ready-to-use models for buildings and other structures, bringing the real world into BIM.
Increasingly, BIM will be used in the refurbishment of existing buildings and it is in this area that HDR offers a number of benefits. It enables precise capture of high definition 3D data that can be used to create a parametric 3D BIM model using the precise depiction of the real world from HDR camera technology, in the form of a point cloud. It is then possible to use the point cloud as a modelling reference, enabling various views of the point cloud to be extracted. It is also possible to create high resolution images as well as spatial and panoramic model views of the asset. On a practical level, too, our SceneCentre Overlapping HDR 360 images create a ‘Virtual Tape Measure’ function allowing measurements to be taken from any authorised PC or tablet.
Tunnel vision
In July 2017, L&M was asked to complete an inspection survey of a working railway tunnel in the East Midlands. The Spheron SceneCam solution was chosen as the best tool for the job due to its 32-bit High Dynamic Range (HDR) ‘SceneCam’ camera and its battery powered ‘ScanLight’ lighting system, which would be able to capture all the detail present despite the complete darkness.
A two-person team, using three HDR cameras, was deployed and completed the survey of the approximately 1,000m long tunnel over three nights. Imagepairs were recorded every ten metres at chainages that had been marked out with survey chalk and referenced to a milemarker, located just outside the tunnel. Three image locations were captured simultaneously and the cameras then moved on to the next three loca tions.
The SceneCam images were supplemented with additional images captured using a standard frame digital camera. The images captured the whole tunnel environment and the standard frame camera captured sub-surface details like the insides of catch-pit chambers and inside the covered cable-housing. The SceneCam camera captures a single, continuous image around a full 360 degrees in the horizontal and 300 degrees in the vertical, using a slit aperture and a fish-eye lens. No stitching of images is required. The camera captures 26 F-stops simultaneously. In daylight this would capture all the lighting conditions present, allowing the viewer to look into the darkest shadow yet still retain detail in the brightest areas. On this occasion it allowed the viewer to brighten the data from dark conditions to a detailed, vibrant data-set.
Once the fieldwork was complete the processing began, and this could be carried out on site. The images required no ‘cloud-processing’ so all data was retained by the operator. The spherical images were imported directly into Spheron’s own SceneCenter software. This software was used to prepare the deliverable for the project – a complete visual tour of the tunnel. The spherical data set was added to by importing the additional images and then PDF drainage reports of the catch pits and other reports too, all of which could be viewed within the software. Once complete the report allowed the viewer to navigate through the tunnel in a similar way to Street View. The viewer could increase the brightness, zoom in, open reports and measure dimensions straight from the images (possible due to the capture of stereo- pairs on the same location). All this amounted to a new form of deliverable that simply could not have been captured or presented using any other means.
A glimpse of the future
High Dynamic Range imaging is set to grow in popularity — the benefits are simply too obvious to ignore — however, most of today’s digital cameras used in the surveying sector are not yet HDRcapable. To create HDR image files, several shots of the same scene at different exposures have to be taken and advanced software then used to create an HDR image. LDR survey cameras are unable to do this.
As such, a revolution in visual data capture in the surveying sector has been long overdue, although it was always going to happen because of the limitations of LDR and the fact that advances in BIM rely on precise, real-life images. Latest HDR camera surveys now have the capability of feeding better quality information into the BIM process, from the beginning of the project, all the way through to the handover of documentation. Our clients are constantly asking for more site information because it saves time and money at every stage of the project. That’s one of the reasons why we added spherical HDR imagery to the normal topographic survey deliverables, 2D, 3D drawings and Revit Models as well as complete site, full colour 360 tour with the ability to take dimensions from anyone’s desktop. Any documentation can be attached to the spherical images, from survey data and drawings, as-built information, reports, safety notes or handover documentation. All in a simple- to-use interface that anyone can use without having a CAD licence or specialist software, from wherever they sit.
It is foreseeable that BIM will soon require all inputted information to be from HDR technology, certainly for those that require accurate point cloud presentation of data. In itself, high dynamic range imaging offers a radically new approach of representing survey data. Instead of using the range of fixed colours and limited range of exposures, HDR manipulates and stores all colours and brightness levels visible to the human eye.
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