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Fixing Albers projection bounds checking for southern hemisphere CRS's. #337

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Merged
juliohm merged 2 commits into from
Jan 2, 2026
Merged

Fixing Albers projection bounds checking for southern hemisphere CRS's. #337

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aea5449
Updated albers.jl renamed `ambers` to `albers`. refactored _albersρ t…
souma4 Jan 1, 2026
8f5ff44
update to throw in _albers\rho just in case
souma4 Jan 2, 2026
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37 changes: 19 additions & 18 deletions src/crs/projected/albers.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -64,9 +64,9 @@ function inbounds(::Type{<:Albers{latₒ,lat₁,lat₂,Datum}}, λ, ϕ) where {l
ϕ₁ = oftype(λ, ustrip(deg2rad(lat₁)))
ϕ₂ = oftype(λ, ustrip(deg2rad(lat₂)))

C, n = _ambersCn(ϕ₁, ϕ₂, e, e²)
ρ = _ambersρ(ϕ, C, n, e, e²)
ρ ≥ 0
C, n = _albersCn(ϕ₁, ϕ₂, e, e²)
ρ² = _albersρ²(ϕ, C, n, e, e²)
ρ² ≥ 0
end

function formulas(::Type{<:Albers{latₒ,lat₁,lat₂,Datum}}, ::Type{T}) where {latₒ,lat₁,lat₂,Datum,T}
Expand All @@ -77,10 +77,10 @@ function formulas(::Type{<:Albers{latₒ,lat₁,lat₂,Datum}}, ::Type{T}) where
ϕ₁ = T(ustrip(deg2rad(lat₁)))
ϕ₂ = T(ustrip(deg2rad(lat₂)))

C, n = _ambersCn(ϕ₁, ϕ₂, e, e²)
C, n = _albersCn(ϕ₁, ϕ₂, e, e²)

θ(λ) = n * λ
ρ(ϕ) = _ambersρ(ϕ, C, n, e, e²)
ρ(ϕ) = _albersρ(ϕ, C, n, e, e²)
ρₒ = ρ(ϕₒ)

fx(λ, ϕ) = ρ(ϕ) * sin(θ(λ))
Expand All @@ -98,15 +98,11 @@ function forward(::Type{<:Albers{latₒ,lat₁,lat₂,Datum}}, λ, ϕ) where {la
ϕ₁ = oftype(λ, ustrip(deg2rad(lat₁)))
ϕ₂ = oftype(λ, ustrip(deg2rad(lat₂)))

C, n = _ambersCn(ϕ₁, ϕ₂, e, e²)
ρ = _ambersρ(ϕ, C, n, e, e²)

if ρ < 0
throw(ArgumentError("coordinates outside of the projection domain"))
end
C, n = _albersCn(ϕ₁, ϕ₂, e, e²)
ρ = _albersρ(ϕ, C, n, e, e²)

θ = n * λ
ρₒ = _ambersρ(ϕₒ, C, n, e, e²)
ρₒ = _albersρ(ϕₒ, C, n, e, e²)

x = ρ * sin(θ)
y = ρₒ - ρ * cos(θ)
Expand All @@ -122,8 +118,8 @@ function backward(::Type{<:Albers{latₒ,lat₁,lat₂,Datum}}, x, y) where {lat
ϕ₁ = oftype(x, ustrip(deg2rad(lat₁)))
ϕ₂ = oftype(x, ustrip(deg2rad(lat₂)))

C, n = _ambersCn(ϕ₁, ϕ₂, e, e²)
ρₒ = _ambersρ(ϕₒ, C, n, e, e²)
C, n = _albersCn(ϕ₁, ϕ₂, e, e²)
ρₒ = _albersρ(ϕₒ, C, n, e, e²)

θ = n ≥ 0 ? atan(x, ρₒ - y) : atan(-x, y - ρₒ)
ρ′ = sqrt(x^2 + (ρₒ - y)^2)
Expand All @@ -140,7 +136,7 @@ end
# HELPER FUNCTIONS
# -----------------

function _ambersCn(ϕ₁, ϕ₂, e, e²)
function _albersCn(ϕ₁, ϕ₂, e, e²)
m₁ = _albersm(ϕ₁, e²)
m₂ = _albersm(ϕ₂, e²)
α₁ = _albersα(ϕ₁, e, e²)
Expand All @@ -150,9 +146,14 @@ function _ambersCn(ϕ₁, ϕ₂, e, e²)
C, n
end

function _ambersρ(ϕ, C, n, e, e²)
α = _albersα(ϕ, e, e²)
sqrt(C - n * α) / n
_albersρ²(ϕ, C, n, e, e²) = C - n * _albersα(ϕ, e, e²)

function _albersρ(ϕ, C, n, e, e²)
ρ² = _albersρ²(ϕ, C, n, e, e²)
if ρ² < 0
throw(ArgumentError("coordinates outside of the projection domain"))
end
sqrt(ρ²) / n
end

_albersm(ϕ, e²) = cos(ϕ) / sqrt(1 - e² * sin(ϕ)^2)
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