This location of a center point of reference of a fingerprint is used to indicate how centered a fingerprint is for registration or orientation by the AFIS algorithms, as a feature in annotation, and for quality measurements. Although the core may serve some of the same purposes, a center point of reference is defined for arches and also provides a single center location for complex whorls. The center point of reference does not apply to palmprints or plantar impressions.

The center point of reference is the sole EFS feature that can be located outside of the Region of Interest; as such, it allows the estimated center of the finger to be marked even for an extreme side or tip. The center point of reference must be within the bounds of the overall image itself.

The location of a center point of reference can be determined using different approaches. When practical, use the uppermost point of the ridge with greatest curvature approach. Otherwise, use an estimate of the approximate center of the distal fingerprint pad, with a radius of uncertainty. For extreme tips, lower joints, or any cases where the center of the distal fingerprint pad cannot be estimated, indicate the lateral centerline of the finger.

The center point of reference is marked if EFS Profile 3: Detailed Markup Profile is to be used.

Uppermost point of the ridge with greatest curvature

For a fingerprint with a known or estimated orientation, determine the center point using the following process:

1) Find the highest point of each ridge that is convex and pointing upward.

2) From that point, trace the ridge about 3 ridge widths in both directions. Create a line from the high point to the end of each trace, then measure the angle between the two lines to find the peak angle.

3) Compare the curvatures of the ridges. The point with the minimum angle (greatest curvature) is the center point of reference. (See Figure 2.)

Estimate of approximate center of the distal fingerprint pad

When the ridge structure is not clear, estimate the center of the distal pad of the finger. Measure halfway vertically between the crease and the tip, and halfway horizontally across the finger. This is the center of the physical finger, not the center of the print as seen in the image.

Lateral centerline of the finger

For arches, tips, and lower joints, if the vertical center can not be determined but the approximate horizontal centerline of the finger can, mark the lateral centerline. The lateral center is only meaningful if the orientation is known or can be estimated.

Determine whether you want to mark a center point of reference or a lateral centerline, then select that tool. For the center point of reference, click on the center point, then click again to set a radius of uncertainty. For a lateral centerline, the mouse’s vertical position doesn’t matter. Click anywhere along that vertical line to set the lateral centerline.

Setting another center point of reference or lateral centerline will erase any existing markings. You can also use the Delete tool to clear your marking.