FA-70164 / Map projection transforms / Member archive

Spherical polar stereographic forward: south aspect northing sign · case 04

The south polar grid is mirrored top to bottom.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input [lon, lat, pole, lon0, k0]. pole "N" accepts lat >= 0 and "S" accepts lat <= 0; other points return None. Sphere R = 6371000, dl = rad(lon - lon0). North: rho = 2*R*k0*tan(pi/4 - phi/2), x = rho*sin(dl), y = -rho*cos(dl). South: rho = 2*R*k0*tan(pi/4 + phi/2), x = rho*sin(dl), y = rho*cos(dl). Rounded to 2 decimals.

Why this case matters

Sea-ice, Antarctic and Arctic products are gridded in polar stereographic; a sign slip rotates whole continents.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
control #6	`[-3646684.72, 3180757.54]`	`[-3646684.72, -3180757.54]`	Failed

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