Normalize camera coordinates before blaming calibration

Context

Reprojection error increased toward the edge of the frame. The initial hypothesis was that the intrinsic calibration had drifted.

Observation

The predicted points were normalized pinhole coordinates. The observed points were distorted pixels. Their difference had no coherent geometric meaning.

Experiment

Undistorting the observations and converting both arrays into normalized camera coordinates removed the radial error pattern. The remaining residual was small and spatially unstructured.

Questions

• Should the residual interface encode its coordinate frame in the type name?
• Is pixel-space reporting still useful after the optimization finishes?

Next steps

Add coordinate-frame assertions at the projection boundary and plot both normalized and pixel residuals in the calibration report.