Estimation of the optimal criterion for matching coinciding stria in marks of rifling lands

Algorithms for automatic comparison of the traces of the rifling lands (secondary toolmarks) are currently under active development. The calculation of a quantitative estimate based on the results of the comparison of the similarity of the traces of the rifling lands is also being investigated. Determining the optimal criterion for categorizing striae as “matching” in coincident secondary toolmarks is an actual problem. Our studies have shown that assigning traces to the “matching” class can be performed using Shannon information entropy. In this case, the Shannon entropy is used to estimate the criterion of optimal striae intersection. To carry out a model experiment, a sample of 344 pairs of obviously matching and 344 pairs of obviously non-matching secondary toolmarks was formed. On its basis, 200 validation subsamples were formed. The realizations characterized by the lowest entropy were calculated for each criterion of striae overlap in width (10%–100%, 20%–100%, $\dots$, 100%) for all subsamples. It was shown that for secondary toolmarks on bullets fired from a Makarov pistol, this criterion is the interval of striae overlaps in width from 60% to 100%.