Determining the reference points from an elliptical Gaussian fitted to the subcomponents: the centre of light is given by the relative coordinates Δα and Δδ in Table 2, here denoted by (α₀, δ₀). For images A and C with the same parity, we use the positions of the semi-major and semi-minor axes as denoted by (α₁, δ₁) and (α₂, δ₂). Since image D has opposite parity, we employ (α₁, δ₁) and (α₃, δ₃) as reference point positions in addition to (α₀, δ₀).