Mapping choices abound as traffic and crashes mount

Get smart about technology choices when mapping crash scenes

"We can definitely complete the scene (using an LTI Angle Encoder) a lot faster, and we know for sure it's to scale," adds Manges. "We can include 100 times more points this way than we could measuring it by hand, which took several hours. It (the angle encoder) just makes you more thorough in your job, and more accurate."

GPS and laser scanning systems

GPS technology has been applied to crash scene investigations over the past few years, although it is not a widely used method. AutoDocs, from OPTIMUS Corp. in Silver Spring, Maryland, is an automated crash scene measurement and document system. Using GPS technology, AutoDocs automatically generates a graphical representation of a crash scene that is accurate to less than 2 centimeters.

According to OPTIMUS, this system makes more effective use of manpower resources since only one individual is required for operation. An investigator simply points at crash scene objects, and AutoDocs automatically records the GPS measurements for each point. Then the processing software accurately draws the scene and generates a companion text-based accident report. The report also can be wirelessly e-mailed.

OPTIMUS no longer supports its AutoDocs product, although the company is interested in selling the product licensing.

Laser scanning systems, which tend to be expensive, represent another interesting electronic crash scene measurement method. Basically, a 3D scanner is capable of capturing information from a large area of space. They typically can scan 360 degrees on the horizontal and 150 degrees on a vertical area. These scanners produce a very dense dataset of XYZ coordinates for 3D visualization and measurements. Data files can be huge, containing millions of coordinate points (a typical scan will have more than 9 million points) that are quite accurate. Many of these systems have their own viewing software, or the data can be exported to various other 3D programs.

One offering in this crash measurement category is the DeltaSphere-3000 3D scanner from 3rdTech, located in Durham, North Carolina. In operation, a rotating mirror directs a laser in an arc around the scanning head. This then rotates on a motorized base to produce a 360-degree panorama. As the scanner laser rangefinder scans the scene, in 2 to 15 minutes, it takes millions of exact measurements as well as digital photographs.

Next, SceneVision-3D software, which is bundled with the DeltaSphere-3000 scanner, allows the user to take measurements and convert the data points and photos into a high-resolution 3D depiction of the scene. Once completed, the scene can be viewed from any vantage point, and the distance between any two points can be measured.

Cost of the DeltaSphere-3000 3D scanner is $30,000 to 40,000, and can be purchased with or without color.

3D measurements from photographs

Photogrammetry, the technology of obtaining 3D measurements from photographs, is gaining traction with reconstructionists and traffic investigators since it is a one-person operation and takes a short time to accomplish at a crash scene. It typically involves using a digital camera and close-range photogrammetry software.

Investigators use a digital camera on scene to take photographs from two or more perspective angles that record the 2D positions of specific feature points. The photogrammetry software then uses these photographs to determine the XYZ coordinates of these feature points via a process of photogrammetric triangulation.

Among the benefits of using photogrammetry is the image recording process is very fast, reducing time required at the crash scene. Studies have shown that police officers have, on average, reduced on-scene mapping time by 50 percent using photogrammetry, which is a great asset to officer and motorist safety. The imagery from this method also provides a permanent, irrefutable visual record of the scene. Another key benefit is the ability to measure any objects or items visible in the photos, if needed for litigation later.

Proponents of photogrammetry claim the 3D data accuracy of this method is comparable to total stations but at a fraction of the overall relative cost. For a moderately priced digital camera and close-range photogrammetry software, the price tag is about $2,000, or roughly 20 percent of the cost of a total station.

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