A Thermally Decoupled Planar Calibration Target with Vanishing-Edge Fiducials for Joint Visible–Thermal Camera Calibration

Joint geometric calibration of visible-light and thermal-infrared cameras requires calibration features that can be localized consistently in both spectral bands. Established targets generate infrared contrast at the calibration boundary itself, so lateral heat conduction between thermally dissimilar regions blurs the temperature field precisely where subpixel localization is required. Raising the pattern to break that contact instead introduces sidewalls, which are imaged at every pose except exactly normal incidence. This note describes a calibration-target architecture that displaces the conduction path out of the feature plane using thermally resistive standoffs oriented normal to the calibration plane; drives the fiducial thickness to zero at the calibration boundary, so that no sidewall exists to be imaged; and recesses the background, yielding an admissible viewing range θ_max = arctan(R/H) for a lateral support offset R and recess depth H. All calibration points remain coplanar, so established planar calibration algorithms apply unchanged. A modular implementation is described in which interchangeable, individually heated and individually monitored fiducial modules mate to a keyed connector grid on a rigid baseboard, giving uniform closed-loop thermal contrast, reconfigurable pattern geometry, and detection of failed or mis-seated elements. The architecture has been realized as a circular-fiducial prototype and tested qualitatively; no quantitative characterization is reported here. This is a disclosure of the architecture, published as prior art.