How 3D Laser Scanning Systems are Changing Crime Scene Documentation
Written by Robert S. Galvin   

WHEN IT COMES TO RECORDING A CRIME SCENE, most reconstruction experts would agree that it just takes a significant amount of time. This is a primary reason why so many law enforcement agencies and private reconstruction firms have turned within the past several years to using 3D scene capture technologies. The predominant and highly popular solution is the LIDAR (Light Detection and Ranging), which is also commonly referred to as a 3D laser scanner or terrestrial scanner.

This article appeared in the January-February 2021 issue of Evidence Technology Magazine.
You can view that full issue here.

 

 

An excerpt from Crime Scene Documentation: Preserving the Evidence and the Growing Role of 3D Laser Scanning

While this 3D scanning technology has been around for several decades and has widespread acceptance across many industries, it has been viewed as the next generation of crime and crash scene reconstruction technology among a majority of crime scene investigators and reconstruction experts. The 3D laser scanner is an effective and efficient way to capture most crimes scenes. Usually, when arriving at a crime scene, reconstruction practitioners must decide which parts of the scene are relevant to their case. They need to quickly determine what evidence to photograph as well as measure and collect. Prior to scanning, this process was accomplished using traditional mapping methods such as tape measures, measuring wheels, 35mm cameras, video cameras, and total stations to capture physical evidence indoors and outdoors. However, these mapping methods could take hours or even days to capture relevant parts of a scene, which also means certain key scene details might be missed (Figure 1).1


Figure 1. The 3D laser scanner is well suited for mapping and docuenting crime and crash scenes. (Photo courtesy of Bobby Jones Accident Reconstruction, Knoxville, Tenn.)

Millions of Data Points are Transformed into a 3D Point Cloud
A laser scanner can digitally capture the surrounding environment as well as the shape of physical objects using a line of laser light. It is a way to capture the environment, frozen at a moment in time, to include the conditions of the scene and the exact size and shape of items within. The result is a complete digital three-dimensional representation. The laser scanner produces a line of laser light which sweeps across the screen while sensors continuously record the changing distance and intensity of the returning wavelength shape of the laser line in three dimensions (X, Y, and Z) as it strikes the object. As the laser scanner sweeps across a scene and performs a 360-degree scan, it creates an accurate, spatially correct 3D model comprising millions of points called a “point cloud.” The point cloud can be easily navigated using a standard desktop or laptop computer as a dense representation of the scene is displayed (Figure 2).


Figure 2. As the laser scanner sweeps across a scene and performs a 360-degree scan, it creates an accurate, spatially correct 3D model comprising millions of points called a "point cloud." (Photo courtesy of Eugene Liscio, ai3-3d, Ontario, Canada)

This whole scanning process is very fast, capturing upwards of 750,000 points per second, with scene details down to the millimeter. This data set is what is referred to as a point cloud. The point cloud may contain as many as 10 million points after a scan of about 5 mins, defined in terms of the X, Y, and Z coordinates. The typical file formats of point clouds are ASCII types like XYZ and OBJ, as well as E57, LAS, IGS, and other proprietary file formats.2

Typically, an operator will set up the laser scanner at a scene and move the device several times to accomplish different scans from many angles. Once the point cloud files are created, they are merged into one big three-dimensional representation of the object and then post-processed with various software packages, each designed for a specific application. The end result is the creation of point cloud data that is a precise reproduction of the scanned scene.3

Different Ways to Use 3D Laser Scanners

Terrestrial Scanner
Most common of the various scanners is the terrestrial laser scanner, which is typically mounted on a tripod or, in some cases, can be placed on any flat surface. Terrestrial laser scanners have a wide range of applications and can capture dense point clouds with millimeter accuracy. The goal of a terrestrial scanner is to collect data on an environment or an object’s shape and perhaps its appearance. The 3D scanner’s aim is to create a point cloud of data reflected back from the surface of the object. The resulting data set then can be used to build a 3D model or animation. The 3D laser is well suited for mapping and documenting crime and crash scenes, but also building interiors and exteriors as part of pre-planning efforts.

Airborne (UAVs) LIDAR Scanning
Airborne LIDAR can capture data on Earth’s surface. The UAV (unmanned aerial vehicle), or drone, is equipped with 3D laser scanning technology. Airborne scanning can quickly gather large area data for outdoor crime and crash scenes. These do differ from drones equipped with digital cameras for aerial photos which in some cases can also produce 3D data through another technology called “photogrammetry” (the science of making measurements from photographs).4

Handheld Scanners
The handheld laser scanner is not prevalent within the forensic sector—so far—but they can provide value to investigators with particular, challenging crime scene aspects such as bodies, small spaces, behind or under furniture or vehicle interiors.

Mobile Scanning
Unlike terrestrial scanning, which is performed from a static position, mobile scanning collects geospatial data from a vehicle or person outfitted with LIDAR, cameras, and other remote sensors. Mobile scanning is designed for rapid exterior mapping to collect geospatial data quickly and accurately. It is ideal for asset management, planning, and disaster/major incident management.

Reduced Time at Scenes
Because the laser scanner is so fast at recording a scene, it helps reduce the amount of time for investigators to completely clear a scene while grabbing a huge amount of scene data. The scanner does this far more precisely compared to a measuring tape or a total station. After all, if the measuring tape, for example, isn’t straight, or the total station is not level, this can greatly affect the accuracy of the collected data. Software for creating a diagram of the scanned scene provides a view of the entire scene that can be studied from any viewpoint (Figure 3).


Figure 3. With laser scanning technology, public safety officials, like investigator Weston Hadley, of the Santa Ana, California, Police Department's Collision Investigations Unit, can capture an entire scene—billions of highly accurate data points—in less time than with other technology tools. For crash scenes in particular, laser scanning significantly increases efficiency, saves time, and prevents major shutdowns of intersections and highways for collision investigation. (Photo courtesy of Leica Geosystems)

The reduced time spent recording a scene with laser scanning means it is possible to process more crime scenes, and with fewer people. This results in more efficiency with crime scene processing department-wide along with helping agencies to keep on budget. Another benefit with laser scanning is that it captures and preserves the crime or crash scene as it is. In a crime scene, viewing and analyzing data can allow investigators to revisit the scene virtually anytime, which is extremely beneficial as they uncover new information that emerges in the case. And, it is easy to share the scene with others who may have not been at the crime scene when it was processed. When scanners are used at crash scenes, they yield safety for the reconstruction expert because collisions can be cleared more quickly due to the short amount of time needed to scan a scene. Traffic, congestion, and particularly the chance for secondary crashes is greatly reduced.

Laser Scanning Gives You Tools You May Not Have
The use of 3D laser scanning to map and document crime and crash scenes offers a wide range of benefits to those discussed above, but also some tools you may not have. First, let’s review the key benefits that 3D laser scanning offers:

  • Acquisition of large data sets—Eliminating the need for revisiting the scene
  • Faster, more accurate data acquisition
  • Compressed field-to-office timeline
  • Selected feature extraction and manipulation
  • Security planning analysis
  • Creation of Building Information Models (BIM)
  • Geographic Information Systems (GIS) interaction
  • Data can be viewed, navigated, and analyzed similar to a 3D model in traditional CAD systems5

Second, consider these tools that you get with laser scanning:

  • Take 360-degree photographs of the scene
  • Overlay scan data over photos and make precise measurements between any two points in real time—even while testifying
  • Place a virtual camera at any location in the 3D scan data and view the scene from various points
  • Create a fly-through video to take a jury into a crime scene as an effective way to show different perspectives of a scene and its evidence. The video can also be effective for crash scenes by showing the scene in slow motion, then speeding up the video camera to show the actual speed of a vehicle. This can help demonstrate what the driver saw. And, the video can show the scene in slow motion to allow a jury to study details.
  • All of this information can be used to recreate a crash or crime scene to convey the investigator’s hypothesis as to how the event most likely unfolded.

A significant advantage with scanning is that the photography and scanned data points, registered together, become a compelling communication tool for use with juries. Law enforcement agencies nationwide are using scanning to document crime scenes, show line of sight details, and what scene aspects perpetrators and victims could see from different vantage points (Figure 4).6


Figure 4. A 3D laser scanner, widely used by law enforcement agencies and reconstruction experts, can capture a scene to include the conditions of the scene and the exact size and shape of items within. (Photo courtesy of Trimble.com)

Choosing a Laser Scanner Model
As this technology becomes more widely recognized and used for investigators, reputable organizations like the Forensic Technology Center of Excellence and the National Institute of Justice help provide unbiased information and studies. There are excellent studies to help introduce readers with a basic understanding of 3D laser scanners. The report, “A Landscape Study of 3D Crime Scene Scanning Devices,” offers a view of what 3D terrestrial laser scanning technology was offered at the time, as well as factors impacting the implementation and use of this technology.

One of the report’s key components is a comparison of the capabilities of commercially available 3D laser scanning instruments, their use, benefits, and limitations. It also provides considerations that will affect an agency’s or reconstruction expert’s purchase, training, and use of a laser scanner.7

Preserved Laser-Scanned Scenes are Highly Impactful in Court
The laser scanner is particularly valued for its ability to digitally preserve the stored crime scene point cloud once the scene has been scanned. This enables investigators and anyone else to re-examine the scene and to get additional measurements they may need.

Additionally, a laser scanner lends great objectivity to scene documentation because of its speed and compact nature, meaning that everything in the scene can be documented in its original position. The permanent record provided through scanning allows for detailed crime scene analysis long after the scene itself is gone.

Another tremendous advantage to using 3D laser scanning is the point cloud data it provides. The ability of a forensic team or reconstruction expert to use the laser scanner’s point cloud data in their workflow cannot be overemphasized. By bringing scan data into a software program to register the data points, a photorealistic 3D model can be created that proves invaluable in a courtroom presentation to not just show the jury the crime scene, but to actually bring them to it. A full-color walk-through is possible, allowing attorneys to drop the jury right into the scene so it can see the movements of people and activities as they most likely unfolded. When a case goes to trial, it can be months or years after the crime was committed. Luckily, the 3D model of the original scene remains intact and can be re-examined at any time to see additional information or evidence. The laser scanner is able to document indoor and outdoor scenes in high resolution and with ample measurements of rooms and environments. This powerful capability yields a more efficient workflow in a short timeframe (Figure 5).8


Figure 5. Once a crime scene has been scanned, the point cloud can be imported into CAD software to create a detailed 3D model, such as this scene of a homicide victim in an office. (Photo courtesy of FARO Technologies, Inc.)

Utilizing 3D Data in Court
As with any evidence or documentation from a scene, there is a possibility for it to be presented in court. Fortunately, 3D laser scanning technology has been around for several decades and laser scan data have been accepted in court. There are also many peer-reviewed reports available about the technology as well as published known error rates on these devices. Contacting the laser manufacturers can help provide this information. In preparing to testify, it is good practice to prepare for questions not only about the technology but also if the scanner was in working condition and if the operator handled the equipment properly. These can be answered clearly with ensuring the device is calibrated per the recommendation of the manufacturer as well as operators completing training to be certified in laser scanning.9

Setting Control Points for Any Scene Urged When Using Laser Scanner
A laser scanner is like a total station that functions extremely fast. It can measure distance, direction, and deflection to place a point in space. It does this between 500,000 and 1.5 million times per second, and the scanner establishes all of the point positions from an arbitrary origin, which is why all of the data points taken from a scan will be accurate relative to the scanner’s original position. However, according to Senior Trooper William Bush, an Oregon State Police District Lead Reconstruction expert, “Where we start having issues is when you start moving the laser scanner. And we always move it.”

Bush is a fervent advocate of establishing control points for any scene he will map and document because, he argues, this is how accuracy of the data collected can be assured. Too many laser scanning practitioners count on their post-processing software to calculate a best-fit model to combine multiple scans, Bush said. Therefore, instead of reconciling multiple scans back to a set of shared, fixed knowns, these scanner users try to reconcile datasets by letting the software determine how the arbitrary clouds fit. This is a risky move, cautioned Bush. “The problem is that the user may not know how well, or if, the software is giving him the degree of uncertainty about each individual scan’s fit as the scanner is repositioned while mapping a scene,” he added. In such an instance, it doesn’t matter what reconstruction tool is being used because it is still essential to have the same, absolute fixed control positions that are shared among different pieces of technology. And, Bush further adds, it is never a good idea to trust too deeply in any one laser manufacturer. “This (laser scanning) is surveying technology being applied to forensics,” he said. “So, we need to apply survey level control to what we are mapping and documenting at a scene.” After all, Bush continued, “There is never an instance where a surveyor would not control his work.”

Spheres are a way of setting known control points that the post-processing software would recognize, and this is how it is possible to reconcile multiple scans. Scanning projects that use spheres can be more easily solved because the spheres can be used to align the scan data with the photographs that are taken during scanning. Spheres are an effective scanning target. They are hollow, typically made of plastic with a distinctive surface comprised of wear-resistant paint that provides excellent reflection.10

The further away from the origin that a laser scanner is scanning, the more space is being missed, said Bush. Granted, establishing control points takes time, but “as long as the controls are there, captured, it’s just as good to assign them in post-processing than it would be to execute a resection into those controls prior to scanning,” Bush added. The main point here is that the control points still are needed. “We are applying survey industry best practices to the laser scanning of crash and crime scenes and we are asserting that whatever we scan is an accurate representation of the scene,” Bush said. “We are forensic surveyors.”


About the Author
Robert S. Galvin
has been a professional writer for more than 40 years. He has worked as an editor of a community newspaper, and a correspondent for The Oregonian newspaper in Portland, Oregon. In 1989, Galvin launched his own public relations consultancy, which eventually enabled him to work with clients in the law enforcement and public safety sectors. During the last ten-plus years leading up to his retirement, Galvin wrote and published articles that explored the challenges of documenting crime and crash scenes, and how 3D laser scanning, photogrammetry, total stations, and other technology tools proved effective at capturing scenes and their evidence.


Notes

  1. “Laser Scanning for Forensic Investigations.” FARO Technologies UK, 2011. www.faro.com
  2. “Quality Basics – How Does 3D Laser Scanning Work.” 2016. www.engineering.com
  3. “What is 3d Scanning.” www.laserdesign.com
  4. “Drone-photogrammetry-us-lidar.” 2019, October 18. www.wingtra.com
  5. “About 3d Laser Scanning.” www.smartgeometrics.com
  6. Jones, T. “Scanning for Forensic Presentations.” 2011, February 2. www.kci.com
  7. “3d Crime Scene Scanning Devices.” 2018, August. www.forensiccoe.org
  8. “Laser Scanning for Forensic Investigations.” FARO Technologies UK, 2020. www.faro.com
  9. “Hardware 3D Scanners.” www.faro.com
  10. “Basic Reference Sphere Set.” Laser Scanning America, 2020. www.laserscanning-america.com
 
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