Precise accuracy of measurement is the main reason why progressive police departments in
North America have moved from the stretchy measuring tapes of the 80’s and 90’s to total stations for
measuring crash scenes. Migration to this new technology has been a huge improvement but has not
been without introducing a new set of problems. What can be done with the partner that won’t or
can’t hold the target still long enough to get an accurate shot? The Abbotsford Police Department in British Columbia, Canada deploys the equivalent of four full-time Collision Analysts and Reconstructionists. According to these officers, Abbotsford is the home of the worst drivers in North America. This is evidenced by the large quantity of collision scenes that are measured by these officers every year. With significant pressure to get roads open quickly but to conduct thorough investigations, members of the Abbotsford Police Department began experimenting with alternate targets. The Abby-cube is made of 2 inch square aluminum extrusion cut to 2 inch lengths. It is covered with reflective tape on four sides and numbers on two sides over the reflective tape. The cubes are light enough to move around in large quantities, but heavy enough to remain in place in a stiff wind. The multi-purpose Abby-cube is deployed well prior to the measurement process. These cubes provide scene labeling in the photography process and provide excellent orientation for large scenes in the dark. The cubes are set up to mark evidence points and measurement points and also assist with providing evidence descriptions in photographs. After the photography occurs and the measuring begins, the target holder can sit back and watch as the officer operating the total station blast through the scene in minutes. For larger scenes, the “almost” unemployed target holder assists with target selection by standing behind the target cube (at night with a flashlight). This assists the total station officer with selecting the next target in the appropriate sequence. When close points within a large scene are being measured the former target holder can be tasked with taking notes or carrying out other investigative functions such as getting coffee. Acquiring targets in quick succession is one of the strengths of the Abby-cube system. As fast as the total station operator can swing the instrument and focus it on the center of the cube is about how long it takes. A shot every 15 seconds is not out of the question if the MapScenes label is the same. So how does the target acquisition and measuring actually take place? After the cubes are placed, the target height is set at 1 inch (0.025 meters). This is half the height of the actual Abby-cube target. The total station is set in reflectorless mode and aimed at the center of the cube (half the height if a 2 inch cube is 1 inch – the math is easy on this one). Unless there are near hurricane force winds, these cubes are not going to move. For those that don’t use a total station with reflectorless capability, the cubes are covered with 3M high reflective tape that are usually reflective enough for use with a standard total station. Sometimes a measurement adjustment must be made to compensate for the depth of the prism that is missing when used in this mode. If you are looking to purchase Abby-cubes, the prices vary depending on quantity and level of customization. Customized lettering and labeling is available. The important thing to remember is that they are cost effective enough to pay for themselves with use at one or two large collision scenes. The time you will save will be measured in hours. Additional information can be obtained by calling (604) 835-1265 or by emailing dhermann@shaw.ca See more photos of the Abby-cube (1) (2) (3) 
(Part 3 of a three part article) In Part 1 and 2 (Forensic Mapping Challenge)we discussed the identification, documentation and validation of an individual point measurement. The measured points are used to create a database of measurement information from which to create the map. The database is manageable and protected. Remember, to each position the rod person has assigned a code. The code sometimes looks akin to a foreign language. It is really nothing more than an abbreviation for a graphic attribute. The coding can be an a ssignment for a straight line, curved line, (concave or convex) arc or symbol. Most software suppliers provide a default coding library to launch your endeavors and accompanying editor. However not all software is based on the geometry to accurately recreate the scene. Enough emphasis cannot be placed on the responsibility of the rod person. Part of which is the assignment of the forensic code to the measured point. The rod person must be able to visually detect the differences between a straight vs. curved line, crowns, grades, and vertical curves in the area to be documented as well as classification and characterization of physical evidence. In order to map a straight line for example, two points must be measured. Each Point is assigned a forensic code and an instruction to draw a straight or curved line. Traditionally, you use a command code with the graphic instruction to start and stop the line. A code, for example ZEP1, is an instruction to begin a straight line using the graphic instructions found in the library under Edge of Pavement... continued President of McKinzie & Associates, Steve is an active Reconstructionist, specializing in Commercial Vehicle Collision Reconstruction and Forensic Mapping
A MapScenes Pro Yahoo Group was started
in October by Brad Muir and Susan Bracchi. |
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