FA-70265 / Map projection transforms / Member archive

Affine geotransform inverse to pixel indices: column numerator · case 05

Columns drift across rows of rotated rasters.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Input [gx, gy, gt, width, height] with a six-term affine gt: X = gt0 + col*gt1 + row*gt2, Y = gt3 + col*gt4 + row*gt5, where (gt0, gt3) is the outer corner of pixel (0, 0). Invert with the 2x2 determinant, take floor of the fractional column and row, and return [col, row] if inside [0, width) x [0, height), otherwise None (also None for a singular transform).

Why this case matters

Point sampling of rasters and click-to-pixel lookups rely on this inverse; half-pixel or sign mistakes read the neighbouring cell.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
control #12	`[77, 60]`	`[75, 60]`	Failed

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