By Michael L. Selves, Certified Accident Reconstructionist, Certified Trainer and Forensic Mappist, (PSFM)
A multicar pileup occurs at 4 a.m. on a major highway leading to fatalities or devastating injuries. Gun violence erupts downtown resulting in a homicide. In each case, law enforcement officers rush to the site of the incident, ready to reconstruct the crash or crime scene. To understand what caused the crash and to help the crime investigation, you need to capture and preserve the scene as quickly and accurately as possible. It’s essential to have equipment that allows you to work efficiently and with confidence.
Choosing the Right Tools for Your Budget
In a perfect world, all crime and accident reconstructionist would have access to a total station, a GPS unit and a laser scanner. In reality, budget is a constraint. For example, an organization with 60 officers may only be able to allocate $10,000 or $20,000 for these forensic tools. So you have to assess equipment with both functionality and budget in mind.
Four Forensic Tools to Consider
As you review the options, realize that it’s likely that you may need more than one tool. They each have unique features that you can combine for a more comprehensive solution.
1. The Total Station
Total stations use an infrared wave signal to read slopes and measure distances, capturing one point at a time. If you’re documenting small crime scenes and routine crashes, this is a practical tool. They start around $9,000, and when you consider the number of man-hours it would take to reconstruct a scene with a tape measure, this is a budget-friendly tool.
Total stations have a variety of features you need to evaluate:
Go Reflector less to Conserve Man-Hours
Traditionally, total stations required you to set up a prism pole on the object you were measuring from which to reflect the total station’s laser beam. For this process, you need two operators—one to set up the prism and the other to operate the total station. Since most agencies cannot afford to tie up too many officers for forensic investigations, I usually recommend a total station with reflector less capability.
Reflector less total stations can capture distance measurements without a prism as long as the objects you’re measuring are within line of sight. Because you don’t need to set up a prism pole, you reduce the number of people you need on the job and increase safety. If necessary, you can use reflector less total stations with a prism pole for evidence that is out of your line of sight.
A Laser Plummet: Your Eyes in the Dark
Officers have traditionally placed their total stations vertically above a point by using an optical plummet with a bullseye or crosshair. However, at night, when officers’ investigative services are often in demand, it’s difficult to see this guide.
That’s when the laser plummet, which is available on Leica total stations, is especially valuable. It projects a red laser dot on the surface below the total station. Once you’ve chosen the point from which you want to measure, you simply make sure the red dot aligns with it.
Split-Second Shot Time
When it’s 10 degrees outside, in the dark, and you’re standing on the interstate, you want a survey gun that shoots in under a second. And, of course, it’s in the public’s best interest to gather evidence as quickly as possible and re-open the highway before rush hour. Leica total stations make this split-second timing possible. I have not been able to achieve this with any other brands.
Robotic Total Stations Increase Safety
With a robotic total station, you can keep law enforcement personnel at a safe distance by operating it remotely. This is important, for instance, when documenting a vehicle crash on a road, for example, where one lane of traffic is still moving and packed with rubbernecking drivers frustrated by delays.
Keep it Simple
Don’t be taken in by the lure of a total station packed with an extensive list of features. For crash and crime scene reconstruction, it’s more important to choose one that’s easy to use and offers a faster learning curve. Simplicity is one of the reasons I recommend only Leica total stations.
You only get one chance to reconstruct a scene. You cannot tell people that your equipment has broken down and you’ll come back once it’s fixed. While many total stations are unreliable, I’ve never had a problem with Leica’s equipment.
2. The 3D Laser Scanner
The fastest and most efficient piece of equipment for forensic reconstruction is the 3D laser scanner, which only requires one operator. The one I use most frequently is the Leica C10 ScanStation, although I have my eyes on an upgrade to the new Leica ScanStation P40, which is even faster.
Measuring with a laser beam, the Leica ScanStation C10 captures 50,000 points per second, significantly more than a total station. Much like a camera, the laser scanner requires a line of sight to evidence being measured, so you may need to move it around and capture the scene from multiple angles.
Officers don’t have a choice as to when the crash or crime occurs. So, I choose Leica laser scanners because they adapt well to the inclement and challenging conditions in which law enforcement personnel have to work. It may be windy or feel that way because of the cars rushing by. If so, you want an ‘intelligent’ scanner that adjusts for that by using a liquid dual axis compensator (DAC) applies corrections during the scanning process. Also, you need a scanner that won’t fail you in rain, snow or a dusty environment.
While laser scanners are ideal pieces of equipment for comprehensive, accurate documentation, they are, of course, more expensive than a total station. I’ve worked with some agencies who thought laser scanners were out of reach for their budgets. They were, however, able to obtain grants to cover the costs. Given the benefits, it’s worth researching potential grant subsidies.
3. The Multipurpose MultiStation
The Leica MS50 MultiStation is a hybrid tool. It gives you all of the features of a total station to read slopes and distances. In addition, at the touch of a button, you can complete some minor scans. If you’re not expecting to document many multi-vehicle crashes or multi-fatality scenes, then it could provide all the functionality you need.
4. GPS for Open Areas
High-end GPS receivers, accurate to within five millimeters, are useful for mapping large areas. For example, they are used by game wardens who work out in the open and the Royal Canadian Mounted Police. Of course, GPS does not work well if you’re documenting a crime scene in a building.
Combining Tools to Solve Problems
There are occasions when one instrument will suffice, but others may require a combination.
When a crash scene involves multiple vehicles or several fatalities and has a large field of evidence, it will take longer to map the area. In this situation, you need a tool that can capture a substantial amount of detailed information in a short period. The 3D laser scanner can do just that and all from the periphery of the scene.
If, however, you have difficulty seeing a tire mark, footprint, bullet casing or ricochet strike with the naked eye, it will be hard to document with a laser scanner. So, you may also need a total station. You just put the prism pole where the footprint is, document that point and use this to supplement data captured with the laser scanner.
For more information about total stations and high-definition 3D laser scanning solutions for law enforcement and crime scene investigation, please contact us.
Michael L. Selves is the founder of Collision Forensic Solutions, Inc. (CFS) and has over two decades’ experience investigating and reconstructing traffic collisions. CFS provides certified forensic training and has taught numerous law enforcement agencies across the United States. Their offices across the United States are composed entirely of prior and current law enforcement personnel.
This entry was posted in Ready Room and tagged GPS, crash reconstruction, laser scanning, accident reconstruction, total station, crash scene mapping on April 2, 2015 by Michael L. Selves.