"Angular determination of toolmarks using a computer generated virtual tool," J. Forensic Sci., (2015)

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[73]  R. Spotts, L. S. Chumbley,  L. Ekstrand*, S. Zhang, and J. Kreiser, "Angular determination of toolmarks using a computer generated virtual tool," J. Forensic Sci., 60(2), 303-315, 2015;doi:10.1111/1556-4029.12759

Abstract

A blind study to determine whether virtual toolmarks created using a computer could be used to identify and characterize angle of incidence of physical toolmarks was conducted. Six sequentially manufactured screwdriver tips and one random screwdriver were used to create toolmarks at various angles. An apparatus controlled tool angle. Resultant toolmarks were randomly coded and sent to the researchers, who scanned both tips and toolmarks using an optical profilometer to obtain 3D topography data. Developed software was used to create virtual marks based on the tool topography data. Virtual marks generated at angles from 30 to 85° (5° increments) were compared to physical toolmarks using a statistical algorithm. Twenty of twenty toolmarks were correctly identified by the algorithm. On average, the algorithm misidentified the correct angle of incidence by 6.12°. This study presents the results, their significance, and offers reasons for the average angular misidentification. 

"Objective comparison toolmarks from the cutting surfaces of slip-joint pliers," AFTE Journal, (2014)

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[57] T. Grieve, L. S. Chumbley, J. Kreiser, M. Morris,  L. Ekstrand*, and S. Zhang, "Objective comparison toolmarks from the cutting surfaces of slip-joint pliers," AFTE Journal  46(2), 176-185, 2014

Abstract

Experimental results from a statistical analysis algorithm for objectively comparing toolmarks via data files obtained using optical profilometry data are described. The algorithm employed has successfully been used to compare striated marks produced by screwdrivers. In this study, quasi-striated marks produced by the cutting surfaces of slip-joint pliers were examined. Marks were made by cutting both copper and lead wire. Data files were obtained using an optical profilometer that uses focus variation to determine surface roughness. Early efforts using the comparative algorithm yielded inconclusive results when the comparison parameters used were the same as those employed successfully for screw-driver marks. Further experiments showed that the algorithm could successfully be used to separate known matches from non-matches by changing the comparison parameters. Results are presented from the analysis of the copper wires.

"High-resolution, high-speed, three-dimensional video imaging with digital fringe projection techniques," Journal of Visualized Experiments, (2013)

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L. Ekstrand*, N. Karpinsky*, Y. Wang*, and S. Zhang, "High-resolution, high-speed, three-dimensional video imaging with digital fringe projection techniques," Journal of Visualized Experiments (JoVE), (82), e50421, 2013. (Associated with Video Illustrations) (invited); doi: 10.3791/50421

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces. Like the human eyes and brain, DFP uses triangulation between matching points in two views of the same scene at different angles to compute depth. However, unlike a stereo-based method, DFP uses a digital video projector to replace one of the cameras. The projector rapidly projects a known sinusoidal pattern onto the subject, and the surface of the subject distorts these patterns in the camera’s field of view. Three distorted patterns (fringe images) from the camera can be used to compute the depth using triangulation.
Unlike other 3D measurement methods, DFP techniques lead to systems that tend to be faster, lower in equipment cost, more flexible, and easier to develop. DFP systems can also achieve the same measurement resolution as the camera. For this reason, DFP and other digital structured light techniques have recently been the focus of intense research (as summarized in1-5). Taking advantage of DFP, the graphics processing unit, and optimized algorithms, we have developed a system capable of 30 Hz 3D video data acquisition, reconstruction, and display for over 300,000 measurement points per frame. Binary defocusing DFP methods can achieve even greater speeds.
Diverse applications can benefit from DFP techniques. Our collaborators have used our systems for facial function analysis9, facial animation10, cardiac mechanics studies11, and fluid surface measurements, but many other potential applications exist. This video will teach the fundamentals of DFP techniques and illustrate the design and operation of a binary defocusing DFP system.