Use safe_divide for the pole scaling in meters_to_degrees#37
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meters_to_degrees divides the zonal component by cos(lat), which is exactly zero only in the degenerate pole case. Route it through safe_divide so an exactly-zero cos yields 0 with a finite gradient instead of inf/nan. This is a corner-case guard: the flat-Earth longitude scaling genuinely diverges at the poles, and near (but not at) +-90 deg — where cos(lat) is tiny but nonzero — the zonal component is still legitimately huge. The docstring now states this limitation explicitly.
vadmbertr
marked this pull request as ready for review
July 8, 2026 12:19
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Context
meters_to_degreesdivides the zonal component bycos(lat), which is exactly zero only in the degenerate pole case.Scope, stated plainly: this is a corner-case guard, not a fix for the near-pole blowup. At
lat = 90°,cos(radians(90.0))is~6e-17in floating point — not zero — so the result is already a huge-but-finite number today, andsafe_dividedoes not change it (itsdenominator == 0branch never fires).safe_divideonly affects an exactly zero denominator (finite gradient, returns0), and the flat-Earth longitude scaling genuinely diverges at the poles regardless. The docstring now says this outright.Change
cos(lat)division throughsafe_divide.Tests
test_meters_to_degrees_finite_and_safe_at_pole: forward value and gradient finite atlat = 90°.test_meters_to_degrees_unchanged_at_normal_lat: identical to the naive division wherecos(lat) != 0(no regression from the swap).Full suite: 331 passed.