Visual asset surveys using High Dynamic Range (HDR) imaging was, until recently, one of the last remaining frontiers for advancement in the surveying sector. Prior to HDR, when the only available technology was Low Dynamic Range (LDR), the limiting factor with visualisation surveys was that the actual scene being surveyed had a huge dynamic range that couldn’t be completely captured in a single exposure.
Another limitation of LDR technology over the last few decades was that it struggled to keep pace with data requirements, specifically the need for precise, accurate information for inputting into the BIM (Building Information Modelling) process. For instance, LDR cameras have difficulty capturing images 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. That meant if an asset on site was being photographed, either everything inside the building appeared dull and under exposed, whilst a near perfect view through the window was captured. Alternatively, inside the building had the right exposure level – albeit with darker areas on the unlit corners – but with over overexposure in the window appearing as a bright white mass.
For everyday images this may not necessarily be an issue, although with visual asset management in the surveying sector, under and over exposure can result in loss of vital data. The light areas, for example, in the window or the dark corners in the room could be hiding a critical service, fire stop aperture or anomaly within the substrate. 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 surveying of 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 high intensity lighting that can also present H&S issues.
Conversely, HDR (High Dynamic Range) cameras produce images that are revolutionary in terms of quality and content. 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. HDR cameras work by camera capturing 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 and the same 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 white-out area. The end result is an image that is close, or sometimes better, to what the human eye sees.
Apply 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 on a number of areas such as BIM, because it means better quality information us 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 – 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 below.
Building Information Modelling
Building Information Modelling (BIM) is becoming increasingly common on construction projects in the UK. It is now required on all government funded projects over £5m, whilst it is being used to improve the specification, usage and delivery of information on a wide range of other construction projects.
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 and 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.
BIM will also be used more 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 can 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.
Case Study – UK Rail tunnel
We recently completed an inspection survey of a working railway tunnel in the East Midlands using our Spheron HDR SceneCam solution and battery powered ‘ScanLight’ lighting system, which was able to capture all the detail present despite the complete darkness.
A two-person team, using three HDR cameras, were deployed and completed the survey of the approximately 1000m long tunnel over three nights. Image-pairs were recorded every ten metres at chainages that had been marked out with survey chalk and referenced to a mile-marker, located just outside the tunnel. Three image locations were captured simultaneously and the cameras then moved on to the next three locations. 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 HDR 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 was 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 allows 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 can be carried out on site. The images require no ‘cloud-processing’ so all data is retained by the operator. The spherical images were imported directly into Spheron’s own SceneCenter software. This software is 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 can be viewed within the software. Once complete the report allows the viewer to navigate through the tunnel in a similar way to Street-view. The viewer can 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 amounts to a new form of deliverable that simply could not have been captured or presented using any other means.
A revolution in visual data capture in the surveying sector was 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 handover documentation.”