FA-70073 / Map projection transforms / Member archive

Sinusoidal equal-area inverse: pole guard tolerance · case 03

Pixels exactly on the pole rows are reported as outside the map.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input [x, y, lon0] metres on a sphere R = 6371007. lat = y/R radians; if |lat| > pi/2 return None. If cos(lat) < 1e-12 (a pole) return [lon0, +/-90]. Otherwise dl = x/(R*cos(lat)); if |dl| > pi the point is outside the map outline and None is returned. lon = lon0 + deg(dl) wrapped to [-180, 180). Return [lon, lat] degrees rounded to 6 decimals.

Why this case matters

MODIS-style sinusoidal grids are inverted to label pixels; outside-outline pixels must be recognised as fill.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
boundary #15	`null`	`[-45.0, -90.0]`	Failed

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