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fix problem with calculations for southern hemisphere #13

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fix problem with calculations for southern hemisphere #13

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6 changes: 4 additions & 2 deletions src/solar_geometry.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -102,11 +102,13 @@ function solar_azimuth_angle(hour_angle, latitude, declination)
h, ϕ, δ = hour_angle, latitude, declination

tan_azimuth = sin(h) / (cos(ϕ) * tan(δ) - sin(ϕ) * cos(h))
azimuth = atan(tan_azimuth) * sign(latitude)
azimuth = atan(tan_azimuth)

# Correct for hemisphere/quadrant
azimuth = if h == 0.0 # Special case: solar noon
180.0u"°"
# Sun is south when observer is poleward of sub-solar point (denominator < 0
# at h=0), north otherwise.
(cos(ϕ) * tan(δ) - sin(ϕ)) < 0 ? 180.0u"°" : 0.0u"°"
elseif h <= 0.0 # Morning - east of reference
if azimuth <= 0.0u"°"
-azimuth # 1st Quadrant (0–90°)
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