Two LOS velocity components v_LOS1 and v_LOS2 (dashed arrows), measured by each spectrometer at points 4, 5, 6, and 7 in the corona and the reconstructed v_ep (solid arrows) in the epipolar plane (grey). The epipolar plane is defined by the locations of the two spacecraft and the point in the solar corona to be triangulated. v_ep represents the projection of V_3D on the epipolar plane. When projected on LOS1 and LOS2, v_ep represents the velocities v_LOS1 and v_LOS2 measured by each spectrometer.