Henry Templeman - Pattern Force (1/2): Delta Areas

T-Model VERSION 9.2

Inference for

Fingerprint Identification

Based on Match Probability and Relevant Population

Last Update: January 7, 2012

Henry Templeman
henry@henrytempleman.com

Pattern Force (1/2): Delta Areas

Ridge flow forces occur throughout fingerprints and can impact the randomness of ridge formation density and orientation [2]. The presence of certain ridge patterns can force ridges to stop and as a consequence makes ridge orientation less random and more predictable. This phenomenon is known as “pattern force” [13] [103]. Directional ridge formations found in such areas should be considered less rare and therefore possess reduced quantitative weight. The most frequently occurring directional ridge formations found in fingerprints are the ending ridge and bifurcation. The pattern forces most prevalent in fingerprints are found in cores, deltas and diminishing areas.

Delta Areas

For purposes of simplicity, both delta ridge formations were defined as any ridge arrangement found within a 1mm x 1mm area located at the center point of any triradiae ridge formation (delta). It was observed that directional minutiae located around delta formations were impacted by pattern force based on predictable ridge orientation.

A study was performed using 234 flat fingerprints from ten-print files. A total of 139 ending ridges and 94 bifurcations were found between the delta and diverging type lines all with tails oriented towards the diverging types lines. As a result, these minutiae were deemed less random and therefore assigned the same discriminating value as ending and bifurcating ridge units in a diminishing pattern area, e.g., 10 and 18.75 respectively (see Ridge Unit Weights) with corresponding match probabilities as 1/10 and 1/18.75.

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Henry Templeman
henry@henrytempleman.com