TatMapper calibrates one physical plane. It does not reconstruct curvature or guarantee real-world accuracy.
Raw observations and derived results are stored separately. Derived scale must be reproducible from the raw points, physical dimensions, and transforms.
Place a clean U.S. quarter flat, fully visible, and in the same physical plane as the placement. Align the four rim observations. TatMapper uses the official 24.26 mm diameter; it does not guess the denomination. A quarter is quick and widely available, but the camera still needs to be as square to the placement plane as practical.
Place a TatMapper Placement Card in the same plane as the placement. Position the four large numbered handles on the authoritative inner-square corners. TatMapper checks corner ordering, convexity, area, image bounds, perspective severity, reference resolution, and invertibility before creating a rectified working image.
The original normalized photo is preserved. Trace and design geometry use the rectified image coordinate space. Recalibration is available before downstream geometry would become ambiguous.
Coin and custom-round modes use four draggable rim observations. TatMapper checks diameter in pixels, center consistency, and excessive ovality. All single-round-reference methods are sensitive to camera tilt because a circle appears elliptical in perspective. The Placement Card is the backup when four-corner planar perspective correction is preferable.
The manual method uses two endpoints and an entered positive distance. A reference under 12 pixels is rejected; short references receive a warning. Schema-v2 projects migrate to schema v3 as a clearly labelled legacy method and remain usable.