fiducial

A fiducial is a reference point or feature used as a fixed standard for measurements, alignment, or registration. The term, derived from Latin fiducia meaning trust, denotes a known, stable point that provides a coordinate frame or measurement basis across various applications.

In manufacturing and metrology, fiducials are marks placed on objects such as printed circuit boards or precision instruments. They are designed for easy detection by optical systems and serve as reference coordinates for automated assembly, inspection, and dimensional metrology. Fiducials should be highly recognizable and have a well-defined geometry to ensure repeatable positioning.

In medicine and biology, fiducials can be implanted or external markers used to align images from different modalities or time points. In image-guided surgery and radiotherapy, fiducials facilitate accurate targeting by providing consistent reference points for image registration and treatment planning. Fiducials are also used to align serial pathological or microscopic sections in research workflows.

In computer vision and robotics, fiducial markers are artificially designed patterns (such as ArUco or AprilTag markers) placed in a scene. They are detected by cameras to estimate pose and scale, enabling camera calibration, augmented reality, and reliable localization in dynamic environments.

In surveying and geodesy, fiducials refer to known control points or marks that anchor maps and provide a stable reference framework for long-term positional accuracy.

In statistics, fiducial inference is a historical approach proposed by Ronald Fisher to derive probability statements about parameters from data without priors. It remains controversial and is not part of mainstream statistical practice.