ROOT::Math::RhoEtaPhiVector is a typedef to ROOT::Math::DisplacementVector3D<ROOT::Math::CylindricalEta3D<double>,ROOT::Math::DefaultCoordinateSystemTag>

typedef ROOT::Math::DisplacementVector3D<ROOT::Math::CylindricalEta3D<double>,ROOT::Math::DefaultCoordinateSystemTag> | ROOT::Math::RhoEtaPhiVector |