Structure 1
πœƒ en face 𝛳 en face
LAO/RAO CAU/CRA
Structure 2
πœƒ en face 𝛳en face
LAO/RAO CAU/CRA
𝛳 = − arctan [ cosπœƒ - πœƒ en face tan 𝛳 en face ]

𝛳 is the cranio-caudal angle of the optimal projection curve at RAO/LAO angle πœƒ,
𝛳en face and πœƒ en face are, respectively, the cranio-caudal and RAO/LAO angles of the structure viewed en face

Reference:
Xiong T-Y, Pighi M, ThΓ©riault-Lauzier P, et al. Optimal fluoroscopic viewing angles of right-sided heart structures in patients with tricuspid regurgitation based on multislice computed tomography. EuroIntervention. 2019. doi: 10.4244/eij-d-19-00618.