dence have begun to emerge. As part of our charge to consider technical enhancements to the present National Integrated Ballistic Information Network (NIBIN) system—and to ballistic imaging, generally—consideration of three-dimensional measurement versus two-dimensional photography as the imaging standard was a natural pursuit. As Thompson (2006:10, 12) suggests, fully exploiting the three-dimensional aspects of the toolmarks left by firearms raises new levels of complexity relative to two-dimensional photography. “Striated [three-dimensional] toolmarks would be easy to match if, from the beginning to the end, they always stayed the same,” but they do not. Indeed, even fine striations—colloquially referred to as lines—do have a third dimension, depth, that can be appreciated “by using higher magnification”; ultimately, computer-based systems for analyzing striations will have to contend with the problem of deciding whether the different depths of “lines” convey any special significance. Moreover, Thompson (2006:12) notes:
The dynamics of a bullet going down the barrel of a firearm, the downward movement of a fired cartridge case against the breech face of a Glock pistol, or the movement of a screwdriver across a door strike plate all leave 3-dimensional toolmarks that can change considerably in a short distance…. These features, toolmark angle, ammunition variability, [and] tool/barrel wear are features that an examiner considers during an examination and none of these can be [fully] captured in a [two-dimensional] photograph.
In Chapter 8, we discuss experiments conducted on the committee’s behalf by the National Institute of Standards and Technology (NIST) using a prototype three-dimensional sensor on cartridge cases. This chapter provides basic background for that discussion, beginning with a discussion of the conceptual differences between two-dimensional and three-dimensional image acquisition technologies (Section 7–A). Previous efforts in three-dimensional measurement of ballistics evidence are described in Section 7–B, along with currently emerging three-dimensional products (7–C).
A two-dimensional approach to pattern comparison uses a photographic image of the object as the basic element. In considering the impact of two-dimensional imaging on the comparison process, there are several key factors—all driven by the fact that the image is a projection of light