Preserving Evidence with 3D Laser Scanning

The site of a vehicular accident is by all accounts chaotic, with emergency personnel making their way to the scene. Between this response and the subsequent clean-up process, a good deal of potential legal evidence moves, changes or otherwise disappears before investigators can make some headway into what caused the accident.

A new surveying tool is helping forensic engineers and legal teams preserve the scene and its evidence so that detailed and accurate data can be used in causation analysis rather than relying on photographic evidence and field measurements alone.

How it Works

Three-dimensional, high-definition laser surveying (3DLS) uses laser scanning technology to remotely measure spatial data. This technology digitally captures the dimensions and spatial relationship of objects using a line of laser light. The surveys involve collecting horizontal and vertical location points by reflecting light off of objects in a matrix and using that information to calculate the positions of those points on the objects’ surfaces. The scanner outputs a point cloud image, which accurately replicates the scanned objects. The point cloud data provides a highly detailed, accurate three-dimensional representation of ground surfaces, structures, vehicles and anything else in the scene.

This kind of data can be of great value for forensic and legal purposes. Animations and modeling can help reconstruct a scene, but laser surveying uses exact, geo-positioned field data. With laser surveying, all of the spatial relationships and conditions of the scene appear exactly as they did in real life. Dimensions, elevations, depth, length, size and spacing of evidence no longer require photographic interpretation.

Laser scanning offers a number of other benefits.

Speed. Laser scanning involves very little equipment — the scanner and a laptop. A crew of one or two people can get to the scene and set up very quickly. This rapid response prevents the opportunity for changes to the site that a longer delay might allow. In addition, the scanning itself can take as little as a few hours to a day to complete, depending on the scale of the site. Using traditional survey methods, crews often spend days on field measurements, plotting out a grid and measuring data points by hand or using customary survey instruments. Survey crews are often forced to focus only on critical areas and items rather than capturing the entire scene.

Safety. Personnel using traditional surveying methods and instruments must have complete access to all areas involved in the accident scene. This often means complete traffic and lane closures as the survey team needs the ability to either hand measure or make physical observations. This process is very time consuming and involves a great deal of concentrated effort on the part of the field crew to capture important information as well as succumbing to the pressures of an eventual time frame and the need to open the public right-of-way. In fact, the California Department of Transportation “Caltrans” published and developed standards for the use of 3DLS into day-to-day survey operations, having determined the benefits of laser scanning in highway survey applications included a decreased risk of casualties.

A major benefit of 3DLS is the ability to capture existing conditions by non-contact means. Since the laser works on the principal of recording the emission of a calculated laser beam to record the surface of an object, operators can often work safely from the medians, shoulders of roadways and more particularly out of harm’s way of moving vehicular traffic.

Preservation of Evidence. The speed with which laser scanning equipment can detail an accident site is crucial to preserving potential evidence for the ensuing legal case. When accidents occur, investigators using 3DLS can quickly scan a scene and begin piecing elements together before clean-up begins and details are altered.

The technology has proven to be of great value to attorneys and insurance representatives. At an accident scene in Tennessee, state police roped off a scene of a fatal crash, which prevented independent forensic teams from entering the area. The scene was scanned from beyond the tape, collecting data and producing images before the first person entered the site. These scans can accurately document pre- and post-accident conditions and produce a reliable foundation to support the admissibility of any evidence based on them.

Accurate Spatial Relationships. The data produced by 3DLS is so accurate that investigators can clearly determine where all components of a site were located before and after an accident. With traditional site investigations, forensic engineers photograph all angles of a site and piece them together to recreate the position of the elements along with field measurements. But because each photograph is separated and slightly distorted from the next, interpretation is still necessary. That guesswork is eliminated with 3DLS.

Photographic Appearance. The incorporation of digital photos into 3D point cloud data sets has emerged and improved over the past five years. Additional applications of 3D imagery can include the combination of spherical photographs and measureable 3DLS data into a unified data management platform that allow users to virtually tour the site. Coincidence scenes being surveyed can be supplemented with photographs. With the new software systems that are being developed, photographic and point cloud data can be linked with hot spots that give the viewer tour packages with powerful visual interface to link endless types of databases. These systems have proven to be a powerful means to represent findings and conclusions in court.

Processing Data. Perhaps most important is the resulting variety of products the 3D laser scans generate. Not only do they produce rotating 3D scans of a site, but they also can be converted quickly into 2D drawings that are compatible with engineers’ in-house CAD systems. In other words, one scanning session using 3D laser scanning can provide 3D images that can be manipulated to show all points of view, 2D AutoCAD drawings that the engineers can work from, and 3D models that can be used for litigation and court proceedings.

Moreover, the technology can perform scans of undamaged pieces of equipment identical to those that have broken or failed. These scans are then superimposed onto the scans of damaged equipment, providing a better understanding of how accidents occurred. For accident sites like vehicular crashes, this can help forensic engineers immensely.

The most useful thing about laser scanning is during court presentations. After an accident, CAD drawings in combination with 3D scans can be a powerful visual representation of what happened. They show where vehicles were located at certain points and where they hit other objects, working backwards to determine how everything happened.

Mechanism of Failure. Having access to these kinds of vantage points allows investigators to work backwards to determine the order of incidence, or what happened to vehicles as they crashed, all the way back to initiation. In an automobile incident, for instance, 3D scans and CAD drawings can be combined to determine where the vehicles and components were located at certain points along the timeline and where and how they hit other objects. Even more important is the ability to use the recreations to confirm or disprove conditions others may claim.

When called for, 3DLS also allows forensic teams to digitally reintroduce previously removed objects, which can help recreate circumstances more accurately than photos or modeling alone. It is common, for instance, that accident scenes occur in remote or challenging areas. When pieces or evidence are removed from an accident scene, a scanning team can document the evidence in a warehouse or storage yard and place them back into the as-built scene. While this is similar to photographic recreation, scanning provides a much more accurate representation of each element, making the resulting model or simulation more reliable and persuasive.

Legal Lasers

Laser scanning is indeed proving to be an extremely useful tool for legal cases, including everything from vehicular accidents, construction and crane collapses to explosions and fires. Scans can show burn and debris patterns, the conditions of walls and facades, and other potential evidence for these often complex types of cases. In complex property damage and construction accident cases, quick response time and reliable preservation of evidence are often crucial issues. 3D laser scanning is another useful tool in the construction lawyer’s toolbox.