Definitions of the angles and flux-rope geometry. a) Schema defining the angles of the local MC axis direction. It is a local view of panel b). The unit vector points toward the Sun and ẑ_GSE is orthogonal to the ecliptic and northward. φ and θ are respectively the longitude and the latitude of the MC axis (spherical coordinates with the polar axis z_GSE). The axis direction can also be defined by i and λ angles, which are the inclination and the position angle respectively (spherical coordinates with the polar axis x_GSE). β_A is the cone angle defined from to the MC axis. All the angles φ,θ,λ and i are drawn with positive values. b) Schema showing the large-scale meaning of i when the flux rope axis is in a plane (light blue, drawn northward of the radial Sun-spacecraft direction). c) Schema showing the large-scale meaning of λ and drawn in the plane of the flux rope axis. This plane in 3D is inclined by an angle i on the ecliptic (left panels). Examples of spacecraft trajectories across the flux rope are shown with radial dashed lines supposing that the flux rope is expanding radially away from the Sun.