Data processing: measuring – calibrating – or testing – Measurement system – Performance or efficiency evaluation
Reexamination Certificate
2003-01-06
2004-08-31
Hoff, Mark S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Performance or efficiency evaluation
C356S153000
Reexamination Certificate
active
06785634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to computer aided ballistic analysis systems and methods and, more particularly, to a computerized ballistic analysis system and methods in which correlation coefficients obtained by comparing land impression data from the surfaces of bullets is statistically analyzed to evaluate gun identifiability and/or bullet-to-gun classifications.
2. Brief Description of the Related Art
The scratches or striations formed on the surface of a bullet by a gun barrel through which the bullet is fired create a signature with enough unique features that it may be matched with other bullets fired by the same gun. The matching process has been manually accomplished for many years using an optical instrument called a comparison microscope. Manual comparisons of bullets can be quite time consuming and such technique is used sparingly unless there is some reason to believe that a bullet from a crime scene was in fact fired from a gun in question.
Recent machines have been built which attempt to automate the process of ballistics analysis. The goal is to enter bullet images into a database and to allow a computer to search the database for matches. Due to the fact that a computer can make such comparisons many times faster than a human, searching large databases is, at least in principle, feasible. The digitized images of bullets and cartridge cases can also be used to provide additional tools which assist firearms examiners in their manual comparisons.
For example, U.S. Pat. No. 5,654,801 to Baldur describes a fired cartridge illumination method and imaging apparatus which includes a light source and a microscope to image impressions on the surface of the cartridge. Images of the impressions are then used for comparative analysis, during which a first image from a test cartridge and a second image from a computer databank are compared with each other and a maximum correlation value between the first and second images is obtained.
As is common among the current systems capturing data from bullets and cartridges, the devices described in the Baldur patent and in U.S. Pat. No. 5,390,108 to Baldur et al capture strictly visual data which does not distinguish between shallow scratches or deep scratches on the surface of the examined cartridge or bullet. Therefore, important analysis parameters are not considered, which lessens matching reliability and reduces provability of consistent conclusions.
A fundamental problem of all computer aided ballistic analysis systems is that bullets fired from the same gun do not match exactly for a number of reasons, including the facts that the cartridge casing may have different amounts of powder, or that the gun barrel may have been at different temperatures when bullets are fired as compared to the test firing. Due to the fact that the impressions made by a gun on a bullet can differ from firing to firing, all comparison algorithms must necessarily be statistical and cannot look for an exact or even nearly exact match of all striations on the bullet's surface.
Currently, the algorithms which compare bullets have a high false positive match rate. Qualitatively, this means that automatic searching of a large database of ballistic data which may have tens of thousands of entries is not viable. By using the large database, there would be so many false positive matches requiring so many comparisons that essentially no useful information would be obtained. Another problem of current algorithms used in ballistic analysis involves the false negative match rate, resulting in reliable evidence being missed.
The poor false match rate using current algorithms is the result of fundamental problems, most of which are associated with the fact that the data used for the bullet comparisons is 2-D data as represented by the Baldur and Baldur et al patents. 3-D data is much more reliable and robust than 2-D data. In 2-D data capture, a source of light is directed at the bullet's surface, and a camera records the light as it is reflected by that surface. The data capture process is based on the fact that the light reflected by the bullet's surface is a function of its surface features. However, this is an indirect measurement because it involves a transformation of the incident light into the light recorded by the camera. By comparison, a 3-D acquisition process is simply the distance between the surface features and an imaginary plane, and is thus a direct measurement. The disadvantages associated with the indirectness of 2-D data capture are:
Robustness: A significant problem associated with 2-D data capture lies in the fact that the transformation relating the light incident on the bullet's surface and the light reflected by it depends not only on the features of the bullet's surface, but also on a number of independent parameters such as the angle of incidence of the light, the angle of view of the camera, variations on the reflectivity of the bullet's surface, light intensity, et cetera. This implies that the captured data (the data recorded by the camera) is also dependent on these parameters. To attempt to eliminate the effect of these parameters on the captured data would be next to impossible, except possibly for light intensity. As a consequence, the 2-D captured data is vulnerable to considerable variability or, in other terms, it is non-robust.
Indeterminate conditions: A different kind of problem associated with 2-D data capture is the presence of indeterminate conditions in the data. Given an incident light source angle, some of the smaller surface features can be “shadowed” by the larger features. This implies that there will be regions of the surface where the captured data will not accurately reflect the surface features. In mathematical terms, the transformation between the incident light and the reflected light is non-invertible. Furthermore, this is an example where the angle of incidence of the light source can have a critical effect on the captured data, because arbitrarily small changes in the angle of incidence may determine whether smaller features are detected or not. In mathematical terms, the transformation between the incident light and the reflected light is discontinuous with respect to the angle of incidence.
In summary, 2-D data capture methodologies can be affected by extraneous variables that can be next to impossible to control. Moreover, because these variables are not measured, their effects on the captured data cannot be compensated for. As a consequence, the normalized data resulting from some capture processes is also vulnerable to significant variability or, in other words, lack of repeatability. The performance of even the most sophisticated correlation algorithms will be degraded in the presence of non-repeatable data. Taking in consideration that the bullet matching problem is quite demanding to begin with, it is not surprising that ballistic matching methodologies based on 2-D captured data have had significant difficulties delivering satisfactory performance.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to overcome the disadvantages of prior ballistic analysis systems and methods and, in particular, prior computer aided ballistic analysis systems and methods.
Another object of the present invention is to perform ballistic analysis utilizing 3-D information of a bullet's surface.
A further object of the present invention is to perform ballistic analysis by comparing at least the land impressions of two or more bullets and, in particular, by comparing fine details within the land impressions.
An additional object of the present invention is to determine whether a gun is identifiable utilizing matching coefficients and non-matching coefficients obtained by comparing the land impressions of a plurality of control bullets fired by the gun.
It is also an object of the present invention to utilize matching coefficients, obtained by comparing the land impressions of a plurality
Bachrach Benjamin
van Doorn Eric
Hoff Mark S.
Intelligent Automation, Inc.
Raymond Edward
LandOfFree
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