Planning and Positioning of the 3D Laser Scanner
Written by Brenda Butler, CCSA   

WHEN AN AGENCY DECIDES to enter the world of 3D laser scanning to document crime scenes, they often struggle with remembering the best techniques and practices that are available to them. When it comes to training, there is never enough time in the day. We are often multi-tasking to meet the demands required of the complex task of crime scene processing, and that creates a struggle to keep up with the latest developments. Technology is continually advancing and, although it is beneficial to us, it is sometimes a challenge to keep up to date with our skills. This article is a compilation of the best techniques available to the crime scene investigator for documenting crime scenes in the 3D world of laser scanning.

This article is the first in a series intended to answer many of the questions that are continually asked of the author as a forensic solutions specialist for FARO Technologies. The author has more than 20 years of experience as a police officer and 14 years as a crime scene investigator and an evidence technician. This article series will provide helpful techniques and best practices compiled from the author’s experience and the experience of other crime scene investigators across the United States. Even though the technique examples may refer to the FARO laser scanner, the scanning techniques can be utilized by anyone who has a 3D laser scanner and may be applied to any scene, regardless of the manufacturer. Remember, it is always best to refer to your manufacturer’s guidelines and your agency’s protocol when determining the best scanning methods for your specific scanner.

Before you bring your laser scanner into a crime scene, here are some of the things you should know that will assist with preserving and documenting the scene, thus producing a great product for court.

Create a Plan

Before you ever bring the scanner into the scene, you should complete a planning walk-through. Often, we are under time constraints to get the scene done as efficiently as possible, and we need to strike a balance between efficiency and quality. The first step is to establish a plan. When a crime scene investigator arrives at a scene, an initial walk-through is completed to assess the situation, create a plan, and determine if any additional equipment or supplies are needed. The same holds true for the measuring of the scene, including using a 3D measurement device such as a laser scanner.

When you are ready to scan your scene, conduct another walk-through—only this time, as you walk through your scene, ask yourself what is important in your scene, and ensure the laser scanner captures the most valuable areas. A laser scanner is a line-of-sight device. It can only capture what it sees. It cannot look through things or around things. In a perfect world, it can document every single square inch of your crime scene, but you will sacrifice time. If you have the time, that is great! But often we are demanded elsewhere. We must find a solution. Make sure you look for areas of your scene that lack variation—where everything looks the same. If we have those areas, such as long school hallways with lockers on both sides, a heavily wooded forest, a corn field, or something that just lacks any disruption to the geometrical pattern, we may want to consider adding markers, targets, or registration spheres to make our jobs easier when we want the software to register the scanning project automatically.

A rough sketch of the scene, with placement of the laser scanner indicated with an X, will help you move through the scanning of the scene in a logical manner.

After completing your walk-through, create a rough sketch of the area and identify scan positions that will best capture the areas that you have identified as most important. Remember the laser scanner is a 360° device. Because we have received training in crime-scene photography—which reinforces the use of cameras in the corners of the room or outdoor scene to obtain overall descriptive photographs—we often get into the photographers’ frame of mind when we see something on a tripod. The laser scanner is a different beast. If you move your laser scanner tripod to the exterior corners, you will be depriving yourself of 180° of measurements and documentation. You should move your scanner away from walls and think more about the full circle of scanning when determining the placement of your scans unless the situation requires otherwise.

The laser scanner has the benefit of capturing 360° detail. Take advantage of that by avoiding placement of the device in corners or against walls.

Make sure that your scan placement allows your scans to obtain enough overlap in scans while reducing the amount of over-scanning. The overlap is necessary for your scans to register in software automatically, and over-scanning prevents us from efficiently capturing our scene. Although only greater than 30% of overlap is required, a good guide is to try for a 50% overlap. You should always scan methodically. This is where your walk-through and rough sketch help. If your scans do not register automatically due to not enough overlap or other scene-related issues, you may need to register them manually. If you scanned methodically, it is easier to remember which scans overlap to match them together in the manual registration process. The more scans you have in your scene, the more valuable methodical scanning becomes.

Overlap of each scan is required in order for your scans to automatically register in the laser-scanning software.

3D Laser Scanning vs. Photography

Now that you have a plan, you are ready to begin capturing evidence to build your 3D diagram. As we begin the recommended techniques, you should understand that your agency’s policies and procedures are of the utmost importance. Although suggestions are offered within this article, they should never replace your personal agency’s protocol. Please refer to your agency’s policies and procedures when determining what suggestions you should implement for your personal use.

The scanner does not replace photographs. It is not a camera. It contains a camera, but the sole purpose of that camera is to apply color to your laser data points if you choose to scan in color. All the crime- and crash-scene photography rules apply here, and you should refer to your photography training regarding that process. Always take overall photographs in situ, or as your scene was found. Always take overall photographs of your scene after your evidence is identified and follow through with the evidence-establishing or mid-range photographs and—of utmost importance—your macro or close photographs. The macro photographs are great tools to add to your scan data later if desired for court.

Even when using a laser scanner, remember that all crime scene photography rules still apply. Capture overall photographs of your scene in situ; after your evidence is identified (top); as well as mid-range and macro (bottom) images.

Identify, Mark, and Preserve Evidence

Identify your evidence before you scan. Sometimes we want to preserve the scene with the scanner before processing evidence. That is not the most beneficial use of the laser scanner. Instead, you could use the scanner as a wonderful court-presentation tool, taking the jury to a virtual world and immersing them into the scene as it was found that day. If you were taking hand measurements, you would not measure the scene before locating the evidence. You would locate the evidence first and then measure your scene to document the location of the evidence in your diagram. It is the same if you are taking measurements using a laser scanner. Think about presenting your scanning point cloud to a jury and talking about a piece of evidence within your scene that was very valuable to your case. Do you want the jury paying attention to you and that piece of evidence, or do you want them distracted as they search for the item you are talking about?

Using identifying markers or evidence placards helps you to stay organized on the stand and helps a jury to quickly understand where in the scene the item being discussed is located, and how it relates to your testimony. You should scan your scene after you have identified your items of evidence, after you have identified and labeled your bullet impacts, and after you have inserted trajectory rods into the applicable impacts. You should also scan after the bloodstain patterns have been identified and after they have been mapped. Not only will it enhance your courtroom presentation, but it will also allow for a shooting trajectory analysis or bloodstain pattern analysis to be accomplished later using forensic software if it becomes necessary.

Scan your scene after you have identified and marked the evidence, including bloodstain patterns and bullet impacts.

If exigent circumstances apply, remember that preservation of evidence comes above everything else. Always collect any evidence that is at risk of contamination or destruction. Just leave your evidence marker in place. Then it is easy to show where the evidentiary item was located. If a macro photograph was taken before collection, it could simply be added as an annotation to the 3D scene diagram for demonstration purposes, along with any lab results, reports, or other important information.

Never use chalk to identify your items of evidence. Leave that for the fictional television dramas! Chalk is a powder that can disperse in the air and deposit on evidence, causing potential contamination. It is best to use stickers or markers, but make sure you are not applying them on the evidence, or in extreme proximity of the evidence. Only place stickers or markers near the item to identify it. Also, be cautious around evidentiary items intended for DNA analysis. Make sure your evidence markers are sterilized before using them on any scene. Contamination and cross-contamination of DNA evidence can happen. Always sterilize your tripod legs between scenes. All crime scene processing rules for DNA apply here!

Dealing with Reflections

If you have reflective surfaces, there are additional considerations. Reflective surfaces that can affect the quality of laser scanning include shiny chrome or metal, mirrors, windows with bright sunlight, snow-covered ground, freshly washed vehicles on a bright sunny day…You get the idea. One method is applying craft paper to the mirror. That works if you have the time and resources, but keep in mind that the craft paper will also be visible in your final product. If you are scanning in a controlled environment and have already collected the evidence near the surface that is reflective, a great technique to use is dry shampoo or foot powder to reduce the reflective nature of the surface. Do not coat the item with powder! Not only will that become expensive, but it will look distracting, and it can create a cloud of powder that might counteract what you are trying to accomplish. A light puff is enough; you should barely be able to see it. If you can see it completely coating the surface, you have used way too much. Wait several minutes for the dust to settle before you ever bring your scanner into the area. A great time to apply this technique is when you are conducting your scan-planning walk-through. Then it has enough time to settle any dust particles before scanning.

Find Your Starting Point

Bring your scanner into the scene and place it at your first scan position. Even though the scanner is a 360-degree device, it cannot display the scan on your scanner screen in a circular manner; otherwise, you would not be able to view it completely to determine if you captured the desired scan correctly. Therefore, it needs to have a starting and stopping point to lay out the scan in a complete flat view. To do this, you need to know what the starting and stopping point is for the scanner. In other words, what is 0°, what is 90°, 180° and 360° (which should be the same as 0°)? Determine the most important item to document in that specific scan. Make sure that the point of 0° / 360° is not pointing at that item of importance. It looks awkward when you split a vehicle or a body in half!

Restricted Access

It is important to restrict access to your scene while scanning. Someone in your scene while your scanner is collecting data points can become noise or a distracting partial image. One example is when a supervisor walked through an outdoor scene to observe progress during the last three minutes of a scan where color was applied. During approximately the last three minutes of the scan, the camera was taking photographs to apply color to the data points. The supervisor happened to walk in front of a utility pole at the specific time he was captured by the camera. Since he was not in that position when the data points were collected, the colors of his body and clothing were applied to the pole data points. The circumstance made for a strange-looking utility pole or an awkward-looking human, depending on your perspective! If you do not have complete scene control, make sure your scanner has the “retake picture” function enabled. Doing so will permit you to retake your photographs before finalizing your scan, in the event someone walks through at the wrong time.

Set Tripod Height

Sometimes we set up the tripod and never give it another thought, but the height of the tripod should be adjusted as needed for each scan. Make sure the height of the scanner is appropriate for the area of the most importance on each specific scan. It may require you to adjust the height of the scanner in between scans. A good rule of thumb is to have the scanner body higher than the height of the item of most importance. For example, if I am not concerned with the top of the refrigerator in the kitchen, then I do not need to get the scanner body above the height of the refrigerator. If my concern is what is on the counters and the floor of the kitchen, then my scanner body needs to be above the height of the countertop. And avoid collecting data points on the items of importance at an extreme elongated angle.

When outside, we typically are scanning longer distances and must raise the scanner as high as possible. Doing so also helps capture the tops of vehicles. Keep in mind that if the evidence is outside on the ground, or if the goal is to document a point of impact between vehicles, the scanner body should be lowered to just above those surfaces. Doing so allows for cleaner, more direct laser point contact that helps the scanned project look nicer when it is finished. It is not a hard-fast rule, and each situation will determine the scanner placement.

Look Out Below

Even though the scanner is a 360° device horizontally, it will not scan below the scanner in the vertical rotation. It cannot see through the scanner body under the mirror location. It becomes an important factor in scanner placement. If you place your scanner too close to an item of importance, it might not scan.

A good way to estimate how much distance you need to have between your scanner and an item of importance is to look at the scanner height. The unscanned area underneath the scanner is a diameter equal to the height of your scanner. If it is 4-feet tall, then you will have an unscanned area underneath with a void of about 4 feet, which is 2 feet in every direction from the center. Now, this is not the exact method of calculation, but it is a quick reference of estimation to make it easier for the crime scene investigator to judge the distance from the scanner to objects or surfaces nearby that needs to be included in the scan. If you are scanning methodically as part of your scanning plan, then these unscanned areas will be scanned by the previous scan or the next scan and sometimes by both scans. This is where methodical scanning and scanner placement are very important. It is not enough to hop the scanner through the scene without much forethought—at least, not if you want a great diagram and presentable product!

The unscanned area underneath the scanner is a diameter equal to the height of your scanner.

Navigating Small Spaces

If you find yourself needing to document areas that are very small or low to the ground, such as under a table or a tiny bathroom with limited floor space, do not hesitate to remove the scanner body from the tripod and place the scanner body on the ground or a surface like a countertop. The scanner needs to be free to rotate without striking objects or surfaces nearby. Remember, crime-scene processing rules apply: If you remove the scanner from its tripod, you must protect the tripod quick-connect on the bottom of the scanner from contamination. You do not want to have to clean biological fluids out of your quick-connect. The scanner body can be protected from contamination by placing it on an item that you bring with you, such as a sealed piece of wood, tile, or other items that you have sterilized and can be sterilized or disposed of between your scenes. You can also cover the quick connect with a latex or nitrile glove, but you must make sure it is resting securely and not sitting on the bumpy fingers of the gloves.

Scanning in a confined space can be achieved by removing the laser scanner from its tripod.

Watch for
Part 2: Executing the Scan
in the Winter 2019 issue of Evidence Technology Magazine

About the Author

Brenda Butler is a commissioned police officer in Ohio and a private consultant. She is a state-recognized expert in multiple Ohio counties in areas of investigation, crime scene investigation and reconstruction, 3D laser scanning, bloodstain pattern analysis, and shooting-incident reconstruction. She has processed countless homicide scenes, officer-involved shooting scenes, and everything in between. Butler has worked as a police officer in Ohio for 20 years and a crime scene investigator for 14 years. She is a graduate of the National Forensic Academy Session XXXIV and has a Master’s Degree in Justice Administration from Tiffin University, as well as a Bachelor’s Degree in Executive Public Safety Management (summa Cum Lade) from Cleveland State University. She served in the United States Army (military police). Among other certifications, Butler is a certified crime scene analyst with the International Association of Identification and is a previous deputy director & instructor with the Ohio Peace Officer Training Commission. She is an experienced college instructor and has trained hundreds of police officers on a multitude of topics. Butler currently works as a forensic solutions specialist at FARO and has taught 3D laser scanning and crime scene documentation to police agencies across America.

This article appeared in the Fall 2019 issue of Evidence Technology Magazine.
Click here to read the full issue.

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