Correct east-west distances for latitude (cos(lat) scaling) - #50
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Longitude degrees shrink by cos(latitude); the flat 111 km/deg model overstates E-W positions ~38% at the default Amsterdam center. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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offsetKmFromCenter()in bothradar_display.cppandrunway_overlay.cppconverts the longitude delta to kilometers with the same flat111 km/degfactor as latitude, which is only accurate at the equator — a degree of longitude shrinks bycos(latitude)toward the poles. This overstates all east-west screen positions and distances (aircraft and runways): ~19% at 36°N, and ~38% at this project's own default center (Amsterdam, ~52.37°N).The fix scales the longitude term by
cosf(center latitude)in both files'offsetKmFromCenter; no shared header is introduced, keeping the diff trivially reviewable. Sanity check: 1° of longitude at 52.37°N should be ~67.8 km (111 × cos 52.37°), which the corrected formula reproduces.Heads-up: aircraft will render slightly closer east-west after this change — that's the correction, not a regression. This fix has been running in a fork of this project in daily use with no issues.
(Builds against LovyanGFX 1.2.21; see #49 for why fresh installs currently need that pin.)
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