Principle of tomographic reconstruction method. Top panel: 3D representation of the two reference systems used: the outflow (X, Y, Z) in black and the observer (δx, δy, δz) in yellow. The colored circles illustrate the emitting rings defined by five parameters (see text). The colored dots trace the locations at ϕ = 0 and ϕ = π along the emitting rings. Bottom panels: transverse PV diagrams at δz = 2.5″ across the flow axis and averaged over a slice of ∆z = 0.2″. In the left panel is shown the schematic projection of the colored rings and corresponding colored dots in the PV diagram. Because of the flow inclination, the rings are in fact projected at slightly different heights. Their real projection is studied in Appendix D.1. The white dots in the right panel illustrate the outer limits of the PV diagram. The red curve shows the polynomial fitting of the two edges.