ReCo.jl/src/Geometry.jl

module Geometry

export angle2, norm2d, sq_norm2d

using StaticArrays: SVector

"""
    angle2(a::SVector{2,R}, b::SVector{2,R}) where {R<:Real}

Return the angle `φ` from vector `a` to `b` while `φ` ∈ [-π, π].
"""
function angle2(a::SVector{2,R}, b::SVector{2,R}) where {R<:Real}
    θ_a = atan(a[2], a[1])
    θ_b = atan(b[2], b[1])

    θ = θ_b - θ_a

    return rem2pi(θ, RoundNearest)
end

function sq_norm2d(v::SVector{2,R}) where {R<:Real}
    return v[1]^2 + v[2]^2
end

function norm2d(v::SVector{2,R}) where {R<:Real}
    return sqrt(sq_norm2d(v))
end

end # module