Surveying the scene

Laser scanning and 3D modelling provides a fresh innovative approach to accident investigations. In an article for SHP Matthew Eyre, Dr Patrick Foster and Georgina Speake explained how it works in practice.

 

When an accident happens it is important to gather information about the circumstances that surround it. One of the essential operations that has to be undertaken is a survey of the scene, which provides a record for future reference and captures the scene in the condition when the incident occurred. It is important to perform the survey a soon as possible, as the scene following an accident is in an immediate state of decay.¹

However, a survey should only commence when it is safe to do so and an emergency response has been undertaken. Although accident investigation is paramount across all industries, a survey can vary greatly in respect to scale and in some ways can be governed by the severity of the event itself.²

When conducting an accident investigation survey, it is crucial to consider what information may be regarded as important by the accident investigator and what may be useful for future reference.³ However, not all information gathered may have a direct relation to the cause of an accident.

Little has changed in regard to accident investigation surveying techniques over the last two centuries, with surveyors being tasked to represent a 3D scene using conventional 2D deliverables. This has largely been based on the instrumentation available to investigators and surveyors. The equipment has mainly been linear-based in terms of measurement with theodolites used for angular measurements. This has restricted the possibility of enhancing the survey deliverables, due to subjective, discrete point data collection.

However, recent developments in survey equipment such as laser scanning technology provide high-detail 3D data capture and could have a profound effect on accident investigation.

Laser scanning captures spatial data through laser measurement. A laser scanner has the ability to scan any structure within its field of view and create a 3D representation of the object. The data collected, referred to as a point cloud, can be used to create 2D plans or 3D models of a scene.4

Laser scanner set-up positions should be decided in order to obtain details of the entire reference area. On many occasions, multiple set-up positions are required to survey the entire scene, which are then joined together through the registration process. This involves using common features between set-up positions to produce a complete model.

The resulting data from a laser scanned scene can be very rich. A number of deliverables with reference to accident investigation can be produced including:

• 3D fly through or walkthrough simulations;
• 3D models and scene reconstruction;
• 2D plans and sections;
• views from specific or arbitrary angles (witness verification);
• physical 3D models; and
• videos combining photography, point cloud data and 3D models.

Many of these deliverables can be created directly from the point cloud data. However, 3D models and scene reconstruction require the points to be triangulated to form a solid mesh.
Staged electrocution
To demonstrate the potential of 3D surveying in relation to accident investigation, the author simulated a staged fatal injury. A maintenance worker who had been tasked to replace the metal cage doors on the entrance to a switchgear chamber was electrocuted. A laser scanner and photography were used to demonstrate the advantages of this technology. These offered an accurate, photorealistic reconstruction of the model that could be revisited, while providing the ability to explain the scene to lay people.

When undertaking the survey, digital photographs were taken from the same position in which the laser is emitted from the scanner. This allows the point cloud to be accurately overlaid with the photographs and provides geodetic realism where measurements can be taken.

Photographs were also taken from key locations in the accident area in order to provide additional information.

Using the point cloud and photographs, an accurate 3D model can be produced. The model not only provides additional clarity to the scene, but also the combination of all the above can be made into a video format, which can help navigate around the scene stopping at key areas of interest.

In addition, a 3D model can be used to reconstruct the accident and may help to illustrate the sequence of events prior to the incident, by producing an animation of the events as they unfolded.

Once a 3D model has been created sections can be removed such as the roof of the accident area to demonstrate the locality of elements within the accident.

Although the data is captured in 3D, it can be used to produce 2D deliverables in the form of plans and sections. The 2D deliverable produced from point cloud data is a precise representation of the complex geometry and not an interpretation.

Laser scanner benefits
The benefits that laser scanning offers over conventional survey methods within an accident scene are numerous.

These include 3D data collection, which can be key in the explanation of an environment to people or persons that were unconnected to the event. 3D data allows the observer to see a realistic and spatial view of the full scene, rather than a singular planner view in plan or section.

It is hard to distinguish what is relevant within an accident scene. Data collection using conventional survey methods is subjective and is influenced by the surveyors’ judgement as to what points need to be recorded. Laser scanning methodology will record all visual data within a scene, thereby reducing human error that may occur within the surveying process.

Laser scanning also enables the user to obtain a vast amount of data far more accurately than using conventional methods. The use of a laser scanner can provide a far more comprehensive survey of the scene in comparison to conventional methods. This is of particular relevance when surveying complex structures or unnatural environments. In addition, the dense dataset can provide additional clarity providing the ability to observe the relationship between everything in the accident scene.

An accident survey must be efficient and effective. Modern laser scanners can perform a high-resolution full dome scan in approximately four minutes depending on the make and model, which obviously speeds up the data collection process.

With the use of laser scanning the data is captured and archived. This allows the investigator to revisit the scene virtually any number of times.

Accident scenes can sometimes be unsafe areas in which to operate, for example if a fall of ground or landslip has occurred. Some modern laser scanners offer a large range allowing operation from a safe distance.

When data is collected using a laser scanner, the data can be used as a base to make accurate 3D models.

Using this model, the accident can be reconstructed and different scenarios can be staged and tested within a virtual space, establishing full-incident reconstruction. This can be particularly useful to establish the reach of machinery in relation to the surveyed environment for example.

In terms of witness statement verification/first person viewpoints, a virtual camera can be positioned within an accurate 3D surveyed environment, which enables the user to demonstrate what they may have seen. This can be helpful when it comes to assessing statements.

Depending on the severity of an incident, sometimes the persons involved will be in breach of the law and can be subject to judicial review. Laser scanning gives the ability to demonstrate the scene accurately to an audience that is unconnected to the event, like a jury.

Industry innovation
Laser scanning and 3D modelling does have a place within the accident investigation process as a new methodology for capturing/presenting data, while also providing a real world environment to test possible hypotheses.

Because a laser scanner can capture data in 3D, it offers considerable benefits in terms of clarity and understanding an incident scene. It enables the user to observe the relationships between every object in the environment from any possible angle, which may not be possible in the actual environment.

It also provides an archived record of the scene that can be used to educate others on the ever-changing risks found within the industrial setting.

With the rapid progression of 3D capture technology new software and solutions are being explored daily with innovative new ways to capture and present data for wide ranging solutions. This indicates exciting times ahead from industry developments, where companies aim to secure a competitive edge over rivals.

However, it is important for research to remain ahead of the technological advancements so that safety professionals can examine the reliability and accuracy of new systems of data management and capture, particularly when it comes to accident investigation where the integrity of the data is so important.

Matthew Eyre is a PhD student and Dr Patrick Foster is senior lecturer in mining engineering at Camborne School of Mines, Exeter University. Georgina Speake is an HSE inspector.

References

1. Helmricks, D.R., 2010. Motor Vehicle Accident Forensic Survey. In FIG Congress 2010: Facing Challenges – Building Capacity. Sydney, Australia, pp. 11–16. 
2. Foster PJ, Barnes S, Flumm L, Jobling-Purser J, Stroh F. (2013). Accident Scene Reconstruction in Underground Mining Operations, PositionIT, no. 46 (April/ May), pp30-34 HSE, 2004. Investigating accidents and incidents, HSE.
3. Quintero MS, Genechten BV, Bruyne MD, Poelman R, Hankar M, Barnes S, Caner H, Budei L, Heine E, Reiner H, Garcia JLL, Taronger JMB 2008. 3D Risk Mapping: Theory and practice on Terrestrial Laser Scanning Version
4. Leonardo da Vinci (EU) – Community Vocational Training Action Programme.