LensGrid: measured-domain maps

PASS means supported digital checks passed. It is not optical ground truth or full-frame calibration.

Measured calibration coverage
{
  "training_views": 6,
  "holdout_views": 2,
  "training_hull_area_fraction": 0.32523541162696457,
  "undistort_valid_pixels": 161662,
  "redistort_valid_pixels": 156118,
  "image_pixels": 480000,
  "training_max_view_rmse_px": 8.821957996016209e-06,
  "holdout_max_view_rmse_px": 5.179597609661923e-06,
  "openexr_files": [
    "undistort.exr",
    "redistort.exr"
  ]
}

Coordinate contract

{
  "input_pixels": "top-left origin; first pixel center (0,0); x right, y down",
  "map_channels": "R=(source_x+0.5)/width; G=1-(source_y+0.5)/height; A=valid mask; normalized UV origin bottom-left",
  "array_order": "height,width,2; channel order R,G; rows top to bottom",
  "undistort": "ideal output pixel -> distorted source pixel",
  "redistort": "distorted output pixel -> ideal source pixel",
  "border": "no overscan; source centers inside [0,width-1] x [0,height-1]; invalid RG=0,A=0",
  "support": "distorted sample coordinate inside convex hull of training observations; holdouts never enlarge support"
}