The three coordinates (ρ, φ, θ) are defined as: * 0 ≤ ρ is the distance from the origin to a given point P. * 0 ≤ φ ≤ 180° is the angle between the positive z-axis and the line formed between the origin and P. * 0 ≤ θ ≤ 360° is the angle between the positive x-axis and the line from the origin to the P projected onto the xy-plane. φ is referred to as the zenith or colatitude, while θ is referred to as the azimuth. According to this system, φ and θ lose significance when ρ = 0 and θ loses significance if sin(φ) = 0 (at φ = 0 and φ = 180°.