FA-70007 / Map projection transforms / Member archive

UTM zone and latitude band lookup: band x extension · case 02

Points in the 12-degree band X above 80N are labelled C.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input [lon, lat]. zone = floor((lon+180)/6)+1, with lon=180 mapped to zone 60. Exceptions: lat in [56, 64) and lon in [3, 12) is zone 32; lat in [72, 84] uses zone 31 for lon in [0, 9), 33 for [9, 21), 35 for [21, 33) and 37 for [33, 42). Band letters "CDEFGHJKLMNPQRSTUVWX" (no I or O) cover 8 degrees each from -80; band X also covers up to 84 inclusive. Outside [-80, 84] the band is None. Return [zone, band].

Why this case matters

Grid references, MGRS labels and CRS selection rely on the zone and band, including the Norway and Svalbard exceptions.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
control #2	`[50, "C"]`	`[50, "X"]`	Failed

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